FREQUENCY RECONFIGURABLE LOG-PERIODIC ANTENNA ...

FREQUENCY RECONFIGURABLE LOG-PERIODIC

ANTENNA DESIGN

MUHAMMAD FAIZAL BIN ISMAIL

UNIVERSITI TEKNOLOGI MALAYSIA

FREQUENCY RECONFIGURABLE LOG-PERIODIC ANTENNA DESIGN

MUHAMMAD FAIZAL BIN ISMAIL

A thesis submitted in fulfilment of the

requirements for the award of the degree of

Master of Engineering (Electrical)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

NOVEMBER 2011

iii

Specially dedicated to my beloved mom and dad,

Hjh Arapah bte Osman and Hj Ismail bin Baba,

my siblings and family, for their encouragement and support;

as well as my lovely fiancé, Noraini Khalil and all my friends who always inspired

and motivated me along my excellent journey of education

iv

ACKNOWLEDGEMENT

In the name of Allah, Most Gracious, Most Merciful. Praise be to Allah, the

Cherisher and Sustainer of the Worlds. With His permission I have completed my

Master Degree of Electrical Engineering and hopefully this thesis will benefit the

development of the Ummah all over the world.

Special thanks as well to my project supervisor, Associate Professor Dr.

Mohamad Kamal A. Rahim, for his guidance, motivations, support and constructive

comments in accomplishing this project.

My family deserves special mention for their constant support and for their

role of being the driving force towards the success of my project. My friends

deserve recognition for lending a helping hand when I need them. I would also like

to thank the wonderful members of P18; Mr. Huda A. Majid, Mr. Mohd Nazri A.

Karim, Mr. Osman Ayop, Mr. Farid Zubir, Mr. Amiruddeen Wahid, Mrs. Maisarah

Abu, Mrs. Kamilia, Mrs. Mai Abdul Rahman and Mr. Mohsen Khalily, who have

been extremely kind and helpful throughout my stay. “We don’t remember days, but

we remember moments” and I had a great time and moments with all these guys

during my study in UTM.

My sincere appreciation also goes to everyone whom I may not have

mentioned above; who have helped directly or indirectly in the completion of my

project. A million thanks for all.

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ABSTRACT

The concept of reconfigurable antenna is widely used as additional features of

reconfigurable ability for future wireless communication system. There are various

configurations of reconfigurable antenna such as monopole, dipole and log-periodic

wideband antenna. The integrations of reconfigurable antennas with radio frequency

(RF) switches are needed to perform the switchable ability. In this research, a log-

periodic antenna (LPA) has been designed to perform a wideband frequency

operation by connecting thirteen square-patch antennas using inset feed line

technique. Then, the reconfigurable log-periodic antenna (RLPA) is designed by

connecting positive-intrinsic-negative (PIN) diodes at every transmission lines with a

quarter-wave length radial stub biasing. The representation of real PIN diodes and

the locations of biasing circuits in simulation are also included. Three different sub-

band frequencies with a bandwidth of 20% (3 - 4, 3.7 - 5, and 4.8 - 6 GHz for each

band) are configured from the total of 73% bandwidth (3 to 6 GHz) of the wideband

operations by switching ON and OFF of the PIN diode. Other sub-bands or narrow

band can also be configured by selecting other group of patches. Validation for the

LPA and RLPA is achieved by comparing the simulated and measured radiation

patterns. The measured half-power beamwidth (HPBW) for LPA are 62°, 58° and

72° at frequency 3.4 GHz, 4.0 GHz and 5.8 GHz, respectively, while 73°, 67° and

72° for RLPA at the same frequency band. The simulated gain for LPA and RLPA

are around 4.9 dB and 5.0 dB respectively, while the measured gain is around 5.5 dBi

for LPA and 5.7 dBi for RLPA within a frequency range of 3 – 6 GHz. All the

structures have been fabricated and the measurement results show accuracies of

97.5% for return loss, 80.2% for gain and 98.4% for HPBW with the simulation

results.

vi

ABSTRAK

Konsep antena boleh-ubah telah digunakan secara meluas sebagai

penambahan ciri dalam keupayaan boleh-ubah untuk sistem perhubungan tanpa

wayar di masa hadapan. Terdapat pelbagai konfigurasi antena boleh-ubah

menggunakan antena jenis jalur lebar seperti antena satu-polar, dwipolar dan log-

periodik. Penyepaduan antena dan suis RF diperlukan untuk melaksanakan

keupayaan boleh-ubah. Dalam penyelidikan ini sebuah antena log-periodik telah

direkabentuk untuk operasi jalur lebar dengan menyambung sebanyak tiga belas

antena tampalan segi empat dengan menggunakan teknik kemasukan jalur suapan.

Kemudian, Antena Boleh-Ubah Log-Periodik direkabentuk dengan meletakan diod

PIN pada setiap jalur penghantaran antena bersama dengan pincangan suku

gelombang puntung berjejari. Perwakilan diod PIN yang sebenar dan lokasi litar

pincangan dalam proses simulasi juga disertakan dalam projek ini. Tiga sub jalur

frekuensi yang berlainan dengan lebar jalur sebanyak 20% (3-4, 3.7-5 dan 4.8-6 GHz

bagi setiap jalur) telah dikonfigurasikan dari operasi jalur lebar yang mempunyai 73

% (3 hingga 6 GHz) lebar jalur dengan menukar diod PIN kepada keadaan ON dan

OFF. Sub jalur atau jalur sempit yang lain juga boleh diubah dengan memilih

kumpulan antena tampalan yang lain. Pengesahan untuk LPA dan RLPA tercapai

dengan membandingkan corak sinaran dari hasil simulasi dan pengukuran. Separuh-

Kuasa Lebaralur (HPBW) bagi LPA adalah 62°, 58° dan 72° pada frekuensi 3.4

GHz, 4.0 GHz dan 5.8 GHz manakala sebanyak 73°, 67° and 72° bagi RLPA pada

julat frekuensi yang sama. Gandaan simulasi untuk LPA dan RLPA adalah masing-

masing sekitar 4.9 dB dan 5.0 dB, manakala bagi gandaan pengukuran adalah sekitar

5.5 dBi bagi LPA dan 5.7 dBi bagi RLPA pada julat frekuensi 3-6 GHz. Kesemua

struktur telah difabrikasi dan keputusan pengujian mempunyai ketepatan 97.5% bagi

kehilangan balikan, 80.2% bagi gandaan dan 98.4% bagi HPBW berbanding

keputusan simulasi.

vii

TABLE OF CONTENT

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEGMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURES xiii

LIST OF SYMBOLS xviii

LIST OF ABBREVIATIONS xix

1 INTRODUCTION 1

1.1 Introductions 1

1.2 Project Background 2

1.3 Problem Statement 3

1.4 Objective 4

1.5 Scope and Limitation of the Project 4

1.6 Organization of the Thesis 5

2 LITERATURE REVIEW 7

2.1 Introductions 7

2.2 Antenna Properties 8

2.2.1 Return Loss 8

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2.2.2 Bandwidth 9

2.2.3 Radiation Pattern 10

2.2.4 Half-Power Beamwidth 11

2.2.6 Gain 11

2.3 Wideband Antenna 12

2.3.1 Log-Periodic Antenna 13

2.4 Reconfigurable Antenna 14

2.5 RF Switching 17

2.5.1 PIN Diode Switch 18

2.5.2 PIN Diode Equivalent Circuit Modeling 19

2.5.2 Biasing Circuit 20

2.6 Previous Related Research 23

2.6.1 The Log-Periodic Antenna Development 23

2.6.2 Reconfigurable Using Log-Periodic Antenna 27

2.6.3 Others Reconfigurable Antenna 30

2.7 Summary 37

3 LOG-PERIODIC ANTENNA DESIGN 38

3.1 Introductions 38

3.2 Project Methodology and Flow Chart of Log

Periodic Antenna

41

3.3 Single Patch Antenna Design 43

3.4 The Design of Log-Periodic Wideband Antenna 48

3.5 Parametric Study of Log-Periodic Antenna 51

3.5.1 Simulation on Distance of Adjacent Patch 51

3.5.2 Simulation on Different Length of Inset Feed

Line

53

3.5.3 Simulation on Different Scaling Factor 54

3.5.4 Parametric Studies Conclusion 55

3.6 Summary 56

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4 RECONFIGURABLE LOG-PERIODIC ANTENNA

DESIGN

57


4.2 Project Methodology and Flow Chart 58

4.3 Analysis of PIN Diode Representation 60

4.3.1 PIN Diode Representation using Lumped

Element

61

4.3.2 PIN Diode Representation using PEC Pad 63

4.4 Analysis of Biasing Circuit Location 65

4.4.1 Biasing circuit at the transmission line of

patch

66

4.4.2 Biasing circuit at the middle of length patches 67

4.4.3 Biasing circuit at the back of antenna 69

4.4.4 Parametric Studies Conclusion 70

4.5 Reconfigurable Log-Periodic Antenna (RLPA)

Design

71

4.6 Fabrication Process 78

4.7 Measurement Process 80

4.7.1 Input Return Loss Measurement Setup 80

4.7.2 Radiation Pattern Measurement Setup 81

4.8 Summary 82

5 RESULT ANALYSIS AND DISCUSSION 83


5.2 Analysis Result and Discussion of Log-Periodic

Antenna

84

5.2.1 Input Return Loss 84

5.2.2 Current Distribution 86

5.2.3 Realized Gain and Power Received 87

5.2.4 Radiation Pattern and Half-Power

Beam- width

89

5.3 Analysis Result of Frequency Reconfigurable Log-

Periodic Antenna and Discussion

93

x

5.3.1 Return Loss (S11) 94

5.3.2 Current Distribution 96

5.3.3 Simulated Realized Gain and Power

Received Measurement

97

5.3.4 Radiation Pattern and Half-Power

Beam-width

100

5.4 Overall Discussion 104

5.5 Summary 105

6 CONCLUSION 106

6.1 Overall Conclusion 106

6.2 Key Contribution 108

6.3 Future Research 108

REFERENCES 109

Appendices A - C 116-135

xi

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Parameters value of equivalent circuits for PIN

Diodes

20

2.2 Lumped element’s representation in low and high

frequency

21

2.3 The switches' states of U-Koch reconfigurable

microstrip antenna

32

2.4 Previous researches on reconfigurable antenna 35

3.1 Design description of log-periodic antenna 48

3.2 LPA dimension for each patch. 50

3.3 Result of varying the adjacent patch 52

3.4 Result of varying the length of inset feed line 54

3.5 Summaries result of varying the scaling factor. 55

4.1 The value of lumped elements as a PIN diode 62

4.2 Reconfigurable log-periodic antenna properties 77

4.3 The dimensions for each patches of RLPA. 72

4.4 Switches’ states for each case 75

4.5 Performances of antenna using different PIN

diode representation

77

4.6 Antenna Fabrication Process 78

5.1 Comparison return loss between simulation and

measurement for LPA

86

5.2 Simulated realized gain and efficiency of the LPA 88

5.3 Half-power beam-width for Log-Periodic Antenna 93

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5.4 Comparison of return loss between simulation

and measurement of RLPA

96

5.5 Half-power beam-width for Reconfigurable Log-

Periodic Antenna

104

5.6 Comparison of overall performances in term of

frequency, bandwidth, gain and HPBW between

LPA and RLPA

105

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Coordinate system for radiation pattern measurement 10

2.2 Two-dimensional of power pattern 11

2.3 Reconfigurable Antenna Block Diagram 15

2.4 Cross section diagram of PIN diode 18

2.5 (a) Equivalent circuit for forward biased

(b) Equivalent circuit for reverse biased

19

2.6 Equivalent circuit for a PIN diode 20

2.7 Schematic design of Series SPST Switch 22

2.8 Bias network configuration using radial line stub 23

2.9 Log-Periodic Slot Antenna Array structure 24

2.10 VSWR of Log-Periodic Slot Antenna Array. (Line-

measured, dotted line - computed)

24

2.11 Log-periodic Dipole Fractal Koch Antenna design 25

2.12 Return loss of Log-periodic Dipole Fractal Koch

Antenna

25

2.13 The structure of Log-Periodic Terahertz Antenna 26

2.14 The simulated return loss of Log-Periodic Terahertz

Antenna

26

2.15 Proposed prototype antenna 27

2.16 Measured (a) S-parameter in dB of wideband log

periodic antenna and (b) Efficiency of reconfigurable

antenna

27

2.17 The structure of reconfigurable LPDA (a) the 28

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schematic design and (b) fabricated proposed antenna

2.18 a) Simulated and b) measured return loss response of

the reconfigurable LPDA

28

2.19 Schematic design of reconfigurable log-periodic

dipole antenna with harmonic traps

29

2.20 Measured return loss of reconfigurable log-periodic

dipole antenna

30

2.21 The dimension of annular slot antenna design. The

feeding line with the matching stubs is on the bottom

and the annular slot antenna is on the top side of the

substrate

31

2.22 Simulated and measurement result of reconfigurable

annular slot antenna at three different frequency

31

2.23 Radiation pattern of the reconfigurable annular slot

antenna (a) Simulation (b) Measurement

32

2.24 The structure of U-Koch reconfigurable microstrip

antenna

33

2.25 The measured return loss of U-Koch reconfigurable

microstrip antenna

33

2.26 Geometry of the reconfigurable Vivaldi antenna: (a)

top view, (b) side view, and (c) bottom view.

34

2.27 Measured return loss of reconfigurable Vivaldi

antenna for wideband and sub-band operation

34

3.1 Flow chart of overall process including log-periodic

antenna and reconfigurable antenna

40

3.2 Flow chart of research methodology for LPA 42

3.3 Simulated design of square patch antennas 44

3.4 Return loss of single patch antenna 46

3.5 3-D view radiation pattern of single patch antenna at

3.0 GHz

46

3.6 (a) Polar plot of radiation pattern at 3.0 GHz in E-

plane and (b) Polar plot of radiation pattern at 3.0

GHz in H-plane for single patch antenna with theta

47

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and phi setup in simulation.

3.7 Layout of Log-Periodic Antenna 49

3.8 Dimension of Log-Periodic Antenna 50

3.9 Result of varying distance of adjacent patch (Sa) 52

3.10 Result of varying the length of inset feed line (lf) 53

3.11 Result of varying scaling factor (τ) 55

4.1 RLPA design flow chart 59

4.2 (a) PIN diode representation using lumped element in

single patch antenna. (b) Lumped element data in

CST.

61

4.3 Lumped element circuit that use in CST software (a)

RLC-Serial (b) RLC-Parallel.

62

4.4 Return loss of antenna (lumped element as a PIN

diode)

63

4.5 PIN Diode representation using PEC pad in (a) ON

state (b) OFF state.

63

4.6 Return loss of antenna. (PEC stripe as a PIN diode) 64

4.7 The structure of Antenna A1 66

4.8 Current distribution of Antenna A1 66

4.9 Return loss of Antenna A1 67

4.10 The structure of Antenna A2 67

4.11 Current distribution of Antenna A2 68

4.12 Return loss of Antenna A2 68

4.13 The structure of Antenna A3 (a) front view (b) back

view

69

4.14 Current distribution of Antenna 3 (a) front view (b)

back view

70

4.15 Return loss of Antenna 3 70

4.16 The geometrical structure of reconfigurable log-

periodic antenna

74

4.17 Design description of reconfigurable log-periodic

antenna

74

4.18 Reconfigurable log-periodic antenna design. (a) PEC 76

xvi

stripe as a PIN diode (b) Lumped element circuit as a

PIN diode

4.19 Comparison of PIN diode representation for RLPA in

wideband operation

76

4.20 Return loss measurement setup. (a) Network analyzer

(b) Calibration kit

81

4.21 Power received and radiation pattern measurement

set-up.

81

4.22 Anechoic chamber 82

5.1 Photo of fabricated LPA 84

5.2 Simulated and measured return loss for LPA 85

5.3 Simulated current distribution for LPA at: (a) 3 GHz

(b) 4 GHz (c) 5 GHz (d) 6 GHz.

87

5.4 Measured received of the LPA and the horn antenna 89

5.5 Simulated radiation pattern of LPA at 3.4 GHz (a) 3-

D view. (b) 2-D view in E-plane. (c) 2-D view in H-

plane

90

5.6 Measured radiation pattern of LPA at 3.4 GHz (a) E-

plane. (b) H-plane

90



plane

91


plane. (b) H-plane

91



plane

92


plane. (b) H-plane

92

5.11 Photo of Reconfigurable Log-Periodic Antenna 93

5.12 Simulation and measurement return loss of the

antenna when all switches are in ON state.

94

5.13 Return loss of simulated reconfigurable log-periodic 95

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antenna for different band

5.14 Return loss of measured reconfigurable log-periodic

antenna for different band

95

5.15 Simulated current distribution for reconfigurable log-

periodic antenna at: (a) 3 GHz (b) 4 GHz (c) 5 GHz

(d) 6 GHz.

97

5.16 (a) Simulated realized gain, directivity and efficiency

of RLPA.

(b) Simulated realized gain of RLPA in different

sub-bands.

98

5.17 Power received for different types of antenna at

measurement set-up

99

5.18 Power received of reconfigurable log-periodic

antenna (a) E-Plane (b) H-Plane

99

5.19 Simulated radiation pattern of RLPA at 3.4 GHz (a)

3-D view. (b) 2-D view in E-plane. (c) 2-D view in H-

plane

101

5.20 Measured radiation pattern of RLPA at 3.4 GHz (a)

E-plane. (b) H-plane

101



plane

102



102



plane

103



103

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LIST OF SYMBOLS

fl - Low frequency

fh - High frequency

τ - Scaling factor

E - Electric field.

H - Magnetic field.

h - Substrate thickness.

t - Copper thickness

wp - Width of patch

εr - Relative permittivity of material.

tan δ - Tangential loss of material.

dB - Decibel

lf - Length of inset fed

ltx - Length of transmission line

mm - millimeter

R - Resistor

L - Inductor

C - Capacitor

xix

LIST OF ABBREVIATIONS

LPA - Log-Periodic Antenna

RLPA - Reconfigurable Log-Periodic Antenna

WLAN - Wireless Local Area Network

WiMAX - Worldwide Interoperability for Microwave Access

UWB - Ultra Wide Band

CR - Cognitive Radio

VSWR - Voltage Standing Wave Ratio

RL - Return Loss

BW - Bandwidth

BW% - Bandwidth Percentage

HPBW - Half Power Bandwidth

FR-4 - Fire Retardant Type 4

mm - Millimeter

GHz - Gigahertz

THz - Terahertz

SMA - Sub-Miniature version A

UV - Ultra Violet

CST - Computer Simulation Technology

xx

LIST OF APPANDICES

APPENDIX TITLE PAGE

A List of publications 116

B Datasheet of PIN Diode Infineon BAR 64 117

C Datasheet of wideband horn antenna 134

CHAPTER 1

INTRODUCTION

1.1 Introductions

This thesis proposes the design and development of wideband antenna using

log-periodic technique. The integration of the antenna with PIN diode switches and

lumped elements forms the reconfigurable antenna that enables the antenna to select

several sub-bands from a wideband frequency. This work involves the design,

fabrication and measurement process of the antenna that has wideband frequency

operation with frequency reconfigurability for future wireless communication system

such as cognitive radio, radar system and wireless communication network.

This thesis describes the antenna’s development including the literature

review on the reconfigurable antenna, the simulation design until the fabrication and

measurement process. In this first chapter, the brief background of the project is

discussed, providing problem statements, objectives, methodology, and scope of

work in conducting the research including the project’s possible outcome and

contributions and also the thesis organization.

2

1.2 Project Background

The field of wireless communication nowadays has put more emphasis on the

field of antenna design. In the early years when radio frequency was discovered, an

antenna with a simple design was used as a device to transmit electrical energy or

radio wave through the air in all directions. This innovative way of communication

to replace wired technology to wireless technology was first introduced by Galileo

Marconi when he successfully initiated the first wireless telegraph transmission in

1895 [1]. After that, the development of wireless technology makes leaps and

bounds.

Antenna development play a key role in wireless technology since the rapidly

increasing number of users in broadcasting, telecommunications, navigation, radar,

sensors, military and perhaps for future wireless communication e.g. the cognitive

radio [2]. The increasing number of users may lead to congestion of existing

spectrum such as Wireless Local Area network (WLAN), Wireless Personal Area

Network (WPAN), mobile communication and radio spectrum. Therefore, the

development of a reconfigurable antenna is very interesting in the improvement of

modern wireless communication system because they enable users to provide a

single antenna to be used in many systems.

The advantage of the reconfigurable antenna is they can alter or change the

antenna parameters based on their field of operation. The development of a

reconfigurable antenna is usually related to the microstrip antenna and their

integration with switching circuit. Its advantages include a low fabrication cost, light

weight, low profile, conforming, and compatible with integrated circuits devices [3,

4]. Besides, it can be designed at a specific resonant mode to radiate the required

frequency bands for the applications of wireless communication systems. However,

the new era of wireless communication requires antenna to operate in a wideband

range, possesses good radiation and has switchable ability [5, 6].

3

1.3 Problem Statement

As modern wireless communication systems have developed rapidly in recent

years, an antenna as a front component is required to have a wide band, good

radiation performances and sometimes switchable ability. To obtain the switchable

ability of the antenna, the concept of a reconfigurable antenna was proposed to easily

select the frequency from wideband to narrowband. The reconfigurable

characteristics of antennas are very valuable for many modern wireless

communication and radar system applications, such as object detection, secure

communications, multi-frequency communications, vehicle speed tests and so on.

Besides, the reconfigurable antenna can also operate within multiple systems by just

using a single antenna. For example, a single antenna can be used for both WLAN

2.4 GHz and 5.8 GHz by reconfiguring their dual-band operation.

The RF switch is important parts in development of reconfigurable antenna as

selection devices to makes tunable ability. The modeling of the RF switch in

simulation tools with an antenna also important that can give better results when

comparing with the fabricated antenna. From the previous research on reconfigurable

antenna [7-11], the implementation of real RF switches into the proposed antenna are

limited and not included with the simulation of an antenna. Some researchers have

used an ideal case to simulate the reconfigurable antenna. This project has propose

the development of reconfigurable antenna with integration of real RF switch and its

modeling in simulation to give better results when comparing with fabricated

antenna.

The development of wideband antenna usually uses a monopole structure [7]

because of various advantages: it is low profile, thin and small, has the ability to

produce very wide frequencies and possesses an omni-directional pattern. However,

by using a monopole structure, there has a difficulty on selection of location to

configure from wideband to narrow bands. Therefore, the log-periodic concept is

used to perform a wideband operation since it has directional radiation pattern; it also

easily selects a narrow band frequency since the log-periodic antenna allows a single

patch to radiate at single frequency. The integration of log-periodic antenna with RF

switching circuit can make the reconfigurable antenna even better.

4

1.4 Objective

The main objectives of this project are as follows:

i. Design, simulate and fabricate frequency reconfigurable antenna from

wideband range to narrow band range with integration of real PIN diodes

and biasing circuits.

ii. Design, simulate and fabricate a wideband antenna using log-periodic

technique.

iii. To characterize the antenna parameters in term of input return loss,

radiation pattern, half power beam width and gain for both simulation and

measurement.

1.5 Scope and Limitation of the Project

The main scopes of this research are:

i. Literature review and previous research study on log-periodic antenna and

reconfigurable antenna.

ii. Design, simulate and analyze the log-periodic wideband antenna and

reconfigurable log-periodic antenna using CST Microwave Studio

Software.

iii. Fabricate and measure the log-periodic antenna and reconfigurable log-

periodic antenna. The fabrication part includes soldering the PIN diode

and lumped elements.

iv. Analyze and compare the results between simulation and measurement.

v. Journal and thesis documentation.

5

The limitations of this research are:

i. The range of frequency is limit to 6GHz due to available low cost RF PIN

diode from the manufacturers.

ii. There are multiple parameters can be tuned for reconfigurable antenna.

However, this research only focuses on frequency reconfigurable from

wideband, to narrowband.

iii. The measurements of the antenna are based on available facilities in this

university. The anechoic chamber for radiation pattern measurement can

only measure from 0° to 180° rotation. Hence, only front lobes of

radiation patterns are compared with the simulation.

iv. The switching mechanism of this antenna is using manually by DIP

switch to control the PIN diode.

1.6 Organization of the Thesis

This thesis is divided into six chapters that describe all the work done for this

project. The first chapter consists of the introduction, project background, problem

statement, objectives, scope of study and project contribution. Chapter 2 is literature

review that explains literature about the log-periodic antenna and the reconfigurable

antenna. The basics of the antenna properties such as radiation pattern, bandwidth,

gain and HPBW are presented. The log-periodic concept is introduced and explained

to get a wideband operation before integrated with the lumped elements and PIN

diodes. Besides, the circuit representation of PIN diode and its biasing circuit have

also been explained for reconfigurable purposes. Some overview of previous studies

is also presented.

The design process of Log-Periodic Wideband Antenna is presented in

Chapter 3. The initial result of single patch antenna and the designing process of the

log-periodic wideband antenna are also presented. In order to get an optimum result

in term of return loss and bandwidth, a parametric study by varying the adjacent

distance between the patches, the length of inset feed line and the scaling factor value

6

are presented. While Chapter 3 discusses the passive antenna, the active antenna that

integrated with lumped element is discussed in Chapter 4. In this chapter, the

research flow, design methodology and simulation setup of Reconfigurable Log-

Periodic Antenna is briefly described. The PIN diode representation and biasing

circuit location in RLPA are also presented. This chapter also presents the fabrication

and measurement process of the antenna.

The simulated and measured results of the Log-periodic Wideband Antenna

and Reconfigurable Log-Periodic Antenna are presented in Chapter 5. The simulated

result such as return loss, current distribution, realized gain and radiation pattern is

clearly presented. Then, the measurement process is done to validate the simulated

results and both results have been compared to each other in terms of return loss,

received power and radiation pattern. A discussion of the results is presented clearly.

Lastly, the conclusion of the project is presented in Chapter 6. This chapter concludes

the findings of the project, some key contribution and provides recommendations for

future work.

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

Since decades ago, the reconfigurable antenna received a lot of attention due

to its numerous applications and offers versatility in wireless communication system

such as radar system, cellular-radio system, smart weapons protections, and wireless

local area network system and for future applications including the cognitive radio

system. The reconfigurable antenna is capable of tuneable adjustment on various

antennas’ parameter such as operating frequency, polarization, radiation pattern or

more than one parameter.

In this project, the frequency reconfigurable antenna has been selected to

study the antenna properties before and after integration of the PIN diode. The

frequency reconfigurability needs wideband range to reconfigure to narrow bands.

Hence, to design a wideband antenna, a log-periodic structure has been chosen due to

ease of tuning the frequency. In this chapter, the literature study of the log-periodic

antenna and the reconfigurable antenna is discussed. The important antenna

parameters are also included and discussed in order to understand the antenna

concept before discussing the antennas’ results. This chapter also discusses previous

research on the log-periodic antenna and the reconfigurable antenna to review work

done by other researchers related to this project.

8

2.2 Antenna Properties

The parameters of the antenna play a major role in the performance of the

antenna. These parameters can be modified in the process of designing the antenna to

increase the performance and criteria which is needed for a dedicated application.

There are many parameters that can be measured from an antenna. In this work, only

certain parameters that will be discussed in details due to the lack of equipments and

facilities, but the parameters discussed in this work are sufficient enough to analyze

the performances of the prototype antenna.

2.2.1 Return Loss

The most important parameter to analyze the performance of antenna is the

input return loss. The efficiency of power transmitted to the load via transmission

line is a return loss. In an antenna measurement, the power transmitted of the antenna

can be represent as a Pin while Pref as a power reflection to the source. Ideally, a good

antenna performance is when the power is 100 percent transmitted to the antenna

while 0 percent is reflected back. However, losses in the antenna could reduce the

power transmitted. Hence, the ratio of Pin/Pref is expressed by a return loss using

equation 2.1 below or in term of as shown in equation 2.2 [12-13]. Most of the

journals related in this project [7-9] have defined -10 dB is minimum return loss to

describe the performance of the antenna.

(2.1)

(2.2)

9

2.2.2 Bandwidth

The range of operating frequency within the selected return loss or VSWR is

called the bandwidth of the antenna [1]. There are two ways to represent a bandwidth

which is for broadband antenna and narrowband antenna. For broadband antenna, the

bandwidth is defined as a ratio of the upper-to-lower frequencies of acceptable

operation. As an example, the ratio of 7:1 represents the upper frequencies is seven

times greater than the lower frequencies.

However, for a narrowband antenna, the percentages of the difference

between upper and lower frequency is used over the centre frequency. For the

narrowband application, a 5% bandwidth shows that the difference of the upper and

the lower frequency is about 5% of the centre frequency. It’s also can be calculated

by using these formulas [1]:

!"#$$%&#"' (2.3)

( !&$#&#"' (2.4)

In this project, the designed antenna is a broadband type of antenna. The

bandwidth percentage is calculated as shown in equation 2.5 [1].

( )%100% ×

×−

=lu

lu

ffff

BW (2.5)

where:

fu = upper frequency bandwidth

fl = lower frequency bandwidth

10

2.2.3 Radiation Pattern

The radiation of the antenna is defined as a representation of antenna

performances in term of mathematical and graphical function in free space

coordinates [1]. In other words, radiation pattern is about how an antenna focuses the

energy in space, which represents the coverage area of an antenna itself. The

standard spherical coordinate (r, φθ , ) system is usually used to represent field pattern

of the antenna as shown in Figure 2.4. Radiation pattern can be found in 3D and 2D

plot, but typically 3D pattern is provided by sophisticated simulation software.

However, in practical situation, to measured 3D radiation pattern need sophisticated

Anechoic Chamber and it is too expensive. Nevertheless, a 2D pattern is good

enough to analyze the pattern of the antenna.

Figure 2.1: Coordinate system for radiation pattern measurement [1]

2.2.4 Half-Power Beam

The half-power beam

value that is calculated between two angles from the main lobe [1]. In other words,

the HPBW is measured at the main beam, by calculating the angle of the gain which

has the value of the maximum value minus 3 dB

width is an important parameter for the antenna and

use it. The beam width is always used as a trade

analyze the antenna performance.

Figure 2.

2.2.5 Gain

The gain of the antenna

when the performances of

(AUT) is referred to an antenna which has a

be calculated compared to the reference antenna

antenna. The gain of an antenna

given direction between the AUT and the reference ant

Power Beam-width

power beam width (HPBW) can be defined as

that is calculated between two angles from the main lobe [1]. In other words,

he HPBW is measured at the main beam, by calculating the angle of the gain which

has the value of the maximum value minus 3 dB as shown in Figure 2.2

width is an important parameter for the antenna and is usually referred to when

The beam width is always used as a trade-off between the side lobe levels to

analyze the antenna performance.

Figure 2.2: Two-dimensional of power pattern.

of the antenna is an important parameter that will always be referred

the performances of an antenna is defined. When the antenna

(AUT) is referred to an antenna which has a certain gain value, the AUT’s gain can

be calculated compared to the reference antenna; but it depends on the reference

of an antenna can be defined as the ratio of the power gain in a

given direction between the AUT and the reference antenna with the power input for

11

half the maximum

that is calculated between two angles from the main lobe [1]. In other words,

he HPBW is measured at the main beam, by calculating the angle of the gain which

shown in Figure 2.2. The beam

is usually referred to when users

off between the side lobe levels to

dimensional of power pattern.

is an important parameter that will always be referred

the antenna is under test

certain gain value, the AUT’s gain can

pends on the reference

ratio of the power gain in a

enna with the power input for

12

both antennas are same [1]. The reference antenna could be a horn antenna, dipole

antenna or the others antenna whose the gain can be calculated. The calculation of

the gain is shown in equation 2.6 [1].

)()(

)()(

max

max antennareferenceGantennareferenceP

AUTPdBGGain ×== (2.6)

where;

Pmax (AUT) = Maximum power transmitted from the antenna

under test in watt (W)

Pmax (reference antenna) = Input power of the antenna in watt (W)

G(reference antenna) = Gain of the reference antenna

2.3 Wideband Antenna

Patch antennas suffer from narrow bandwidth which can limit their uses in

some modern wireless application; therefore there is an increasing demand for low

profile and wideband antenna for various future applications. A variety of studies

have come up with different techniques to achieve wideband operation for printed

antennas. Some of the techniques employed are changing the physical size of the

antenna, patch array technique [14], monopole [15], log-periodic technique [8],

adding the U-slot [16], shorting wall [17], folded shorting wall [18], Y-V slot [19],

and staked patch [20]. All these design have been proposed by others researchers to

achieve wide impedance bandwidths [21-25]. Since decade ago, the log periodic

antenna is a most uses by researcher to obtain wideband range referred to its

frequency independent or self-scaling of their dimensions. The log periodic antenna

also suitable for reconfigurable use since each elements of log-periodic antenna are

radiate for each frequency, so that the reconfigurable can be achieved by controlling

every single elements.

13

2.3.1 Log-Periodic Antenna

In the 1950s, antenna evolution advanced into a development of broadband

antennas that have bandwidths greater than 40:1. This antenna’s breakthrough was

referred to as frequency independent or self-scaling and they have geometries that are

specified by angles where the antennas were scaled to change their operating

frequency / bandwidth. In antenna scale modelling, the changing factor of operating

frequency or wavelength is inversely proportional with the physical size of antenna

while the characteristics of an antenna such as impedance, pattern and polarization

are invariant [26]. As an example, if the physical dimensions are reduced by a factor

of three, the performance of the antenna will remain the same if the operating

frequency is increased by a factor of three.

One of the criteria of self-scaling antenna is all the patches or radiator must

be connected with a transmission line and the signal power is connected at high-

frequency end to deliver the power to a lower frequency part. Log Periodic Antenna

is another type of a self-scaling antenna configuration, which closely parallels the

frequency independent concept introduced by DuHamel and Isbell [1, 26]. They

exhibit the same properties at frequencies f and τf. This is possible because the

structure becomes equal to itself by a scaling τ of its dimensions. The structure

works periodically and it would be frequency independent if the variation of the

electrical characteristics over a period is not too significant [3]. The limit of the

bandwidth (low-frequency and high-frequency) is determined by the largest and the

smallest dimension of the structure.

) *+,-*+,

./0,-./0, .,-.,

1,1,- (2.7)

where m = 1, 2, 3, ……

wp = width of patch

ltx = length of transmission line

lf = length of inset fed

F = frequency

14

One of the most important parameters that describe log periodic antennas in

general is the scaling factor. This scaling factor allows the antenna dimensions to

remain constant in terms of wavelength. The design principle of log-periodic

wideband antenna requires scaling the dimensions periodically so that the

performance is periodic with the logarithm of frequency. The patch length (lp), the

width (wp), the inset feed (lf) and the frequency (F) are related to the scaling factor

(τ) by equation 2.7 [26]. The condition is necessary to maintain the same impedance

and radiation characteristics over a wide range of frequencies.

2.4 Reconfigurable Antenna

Microstrip antennas have been closely investigated by researchers to explore

a new structure because of its advantages such as low fabrication cost, light weight,

low profile, conformal, and compatibility with integrated circuits devices [3, 4].

Besides that, it is can be designed at a specific resonant mode to radiate the required

frequency bands for the applications of wireless communication systems. However,

the new era of antenna technology needs the antenna to operate in wideband range,

has good radiation and has occasional switchable ability.

In the past few decades advance technology in microstrip antennas have been

increased especially in incorporating the active components. There has been a

dramatic increase in the awareness of reconfigurable antenna for the applications in

future wireless communication such as cognitive radio [27], ground penetrating radar

(GPR) applications [28], RFID application [29], vehicle speed test [30], secure

communication [31], smart weapon protection [32] and etc.

The advantage of frequency reconfigurable antenna is it can be reconfigured

into any frequency in wideband range and can change dynamically, either

transmitting or receiving on a single antenna instead of using multiple antennas as

usual. For radar application or smart weapon detection, it is advantageous to vary the

beam shaping functionality in that system. Besides that, the reconfigurable antenna

15

can also reduce any unfavorable effects from congested signals especially in ISM

Band (2.4 GHz and 5.8 GHz) and also caused by co-site interference and jamming

effect.

In addition, the development of reconfigurable antenna can reduce the

number or size of antenna used; hence it reduces the power usage and supports the

development of green technology. The most interesting about reconfigurable antenna

is it provides a tunable adjust of the single or more of antennas parameter such as

operating frequency as reported in [32-35], polarization [36-38], radiation pattern

[39-41], and/or two or more of parameters [42-44] in a single antenna. The block

diagram of the reconfigurable antenna is shown in Figure 2.3.

Figure 2.3: Reconfigurable antenna block diagram

Most researchers have designed the reconfigurable antenna for cognitive

radio applications. Hall P.S in [2] has reported that the cognitive radio is a wireless

transponder that has the ability to sense the environment in which it operates and can

adapt itself to optimize its operation. The system could continuously monitor the

spectrum usage in a process which runs parallel with the communication link or use a

single spectrum for spectrum sensing and communication. Therefore, the cognitive

radio system needs antenna that have wideband operation to sense a single spectrum

by reconfiguring the frequency. The reconfigurable antenna that is proposed by Hall

P.S is in one of three ways which is by (a) switching on or turning off parts of the

Antenna

Switch

RF Switch: MEMS

PIN Diode Varactor diode FET transistor

+

Operating frequency

Polarization Radiation Pattern

More than one parameter

16

antenna structures; (b) by changing the antenna geometry by mechanical/electrical

movement and (c) by adjusting the loading or matching of the antenna externally.

The first approach on designing the reconfigurable antenna may employ the

electronic, mechanical or optical switching [45]. However, the efficiency and the

reliability makes the electronic switching more frequently used compared to others.

The electronic switching includes the PIN diodes, FET transistor, varactor diodes or

RF MEMS switches. As reported in [7], the MEMS switches have advantages in

term of isolation and insertion loss compared to the PIN diodes and varactor diodes.

Meanwhile, the RF PIN diodes have low rate of loss and low cost to be employed

with reconfigurable antenna, but it needs to be connected with forward bias direct

current when in the ON state which will degrade the power efficiency and antenna’s

performance.

In [8], the frequency reconfigurability is achieved when the RF switches are

inserted with log periodic aperture fed microstrip antenna. The five bands are

selected from a wideband frequency by switching ON and OFF state at desired

patches. The polarization reconfigurable also has been presented in [36]. A square

patch with two cross-shaped diagonal slots has been designed with three types of

reconfigurable polarization which are a linear, right-handed and left handed. In [40]

the author has presented the pattern reconfigurable from a planar array microstrip

antenna with separated transmission line design.

Besides reconfiguring a single parameter of the antenna, many researchers

have designed an antenna that has more than one configurable parameter. In [42],

the author has designed an annular slot to configure two parameters which are

operating frequency and radiation pattern. By changing the matching stub, three

different frequencies can be reconfigured. The radiation pattern is reconfigured by

controlling the DC voltage of PIN diodes on the slot.

The monopole wideband antenna is also proposed for configuring purposes

[7] because of their advantages; low profile, thin and small, able to produce very

wide frequency and possessing an omni-directional pattern. The cognitive

communication system requires wideband antennas for spectrum sensing and narrow

17

band antennas for transmission which has directional radiation pattern to increase the

performance of signal detection. The development of wideband reconfigurable

antenna with directional radiation pattern has been reported in [8-9]. Furthermore,

the antenna should be well suited in terms of cost, radiation pattern, gain and ease to

integrate with switching circuits.

2.5 RF Switching

The leading technology for reconfigurable system is based on switchable

antenna elements. The reconfigurable antennas are usually equipped with switches

that are controlled by DC bias signals. The switches and the accompanying control

system are very often an integral part of the reconfigurable antenna. The switch

between on and off states of the switches the antenna can be reconfigured to support

a discrete set of operating parameters, e.g. frequency, polarization, radiation pattern.

Each reconfigurable antenna employs a distinct mechanism in order to achieve the

required reconfigurability. Electronic, mechanical or optical switching may be

employed with reconfigurable antennas. Nonetheless, electronic tunability is more

frequently used because of its efficiency and reliability especially in dynamic

bandwidth allocation.

There are various types of RF switches use for reconfigurable antenna such

as RF MEMS, PIN diode and FET transistor where all these types have their own

advantages and disadvantages. As reported in [7], RF MEMS switches have better

performance in terms of isolation, insertion loss, power consumption and linearity

compared to PIN diodes or FET transistors. However, the PIN diode has widely used

by reconfigurable researchers included for this research because of low cost and easy

to fabricate. Besides that, the circuit representations of PIN diodes in simulation also

has presented in [46] where that’s circuit can be used in CST software tools to

compare the antenna’s performances with measurement.

2.5.1 PIN Diode Switch

This research has used a RF PIN diode as a switch component to tune the

reconfigurable antenna because it is a low

This sub-chapter will discuss the overview of RF PIN diode switch and its equivalent

circuit modeling. A microwave PIN diode is a semiconductor device that operates as

a variable resistor at RF and microwave frequency while

component for opening and closing the connection of a circuit or for changing the

connection of a circuit device [47

resistance to current flow in ON state while infinite resistance

Figure 2.4 shows the cross section of a PIN diode which consist of p

semiconductor, n-type semiconductor and intrinsic layer at the middle while metal

pin and glass acts as jacket to cover the PIN diode. The operation of PIN diode ca

be imagined by filling up a water bucket with a hole on the side. The water will

begin pour out when it reaches the hole. Electrically speaking, once the number of

electrons and the number of hole in intrinsic region is equal, the current will be

conducted by the diode since the flooded electrons and holes reaches an equilibrium

point.

When the diode is forward biased, holes and electrons are injected into the I

region. This charge does not recombine ins

in the intrinsic layer. While

behaves like a Capacitance (C

diode in reverse biased [47

biased are discuss in sub

PIN Diode Switch


reconfigurable antenna because it is a low-cost component and easy

chapter will discuss the overview of RF PIN diode switch and its equivalent


a variable resistor at RF and microwave frequency while the switch is an electrical


nnection of a circuit device [47]. Ideally, the function of switch needs zero

resistance to current flow in ON state while infinite resistance in OFF state.

Figure 2.4 shows the cross section of a PIN diode which consist of p

type semiconductor and intrinsic layer at the middle while metal

pin and glass acts as jacket to cover the PIN diode. The operation of PIN diode ca




ed by the diode since the flooded electrons and holes reaches an equilibrium

Figure 2.4: Cross section diagram of PIN diode

When the diode is forward biased, holes and electrons are injected into the I

region. This charge does not recombine instantaneously, but has a finite lifetime (

intrinsic layer. While there is no stored charge in the I-region and the device

behaves like a Capacitance (CT) shunted by a parallel resistance (R

diode in reverse biased [47]. The equivalent circuit based on forward and reverse

biased are discuss in sub-section below.

18


component and easy-to-fabricate.

chapter will discuss the overview of RF PIN diode switch and its equivalent


the switch is an electrical


]. Ideally, the function of switch needs zero

in OFF state.

Figure 2.4 shows the cross section of a PIN diode which consist of p-type

type semiconductor and intrinsic layer at the middle while metal

pin and glass acts as jacket to cover the PIN diode. The operation of PIN diode can




ed by the diode since the flooded electrons and holes reaches an equilibrium

Cross section diagram of PIN diode

When the diode is forward biased, holes and electrons are injected into the I-

tantaneously, but has a finite lifetime ( τ )

region and the device

) shunted by a parallel resistance (RP) when the PIN

lent circuit based on forward and reverse

19

2.5.2 PIN Diode Equivalent Circuit Modeling

The equivalent circuit modeling for PIN diode based on Microsemi [47] is

shown in Figure 2.5. The equivalent circuit for forward biased consist of a series

combination of the series resistance (RS) and a small Inductance (LS) as shown in

Figure 2.5 (a). Series resistance is a function of the forward bias current (If) and this

function can be found in PIN diode datasheet in Appendix B while the small

inductance depends on the geometrical properties of the package such as metal pin

length and diameter. Figure 2.5 (b) shows the equivalent circuit for PIN diode when

reverse biased that consist of the PIN diode Capacitance (CT), a shunt loss element

(RP), and the parasitic inductance (LS).

(a) (b)

Figure 2.5: (a) Equivalent circuit for forward biased (b) Equivalent circuit for

reverse biased

The PIN diode equivalent circuit is an important part in simulation of

reconfigurable antenna to get a result similar to the measurement result. There are

many papers or journals that describe the parameter value of the equivalent circuit by

using appropriate software. In [46], the author has predicted the value of parameter

PIN diode equivalent circuit based on the through-delay-line de-embedding using

Agilent Advanced Design System (ADS) as shown in Figure 2.6 and Table 2.1. The

author has used a micro-semi MPP4203 PIN diode that can operate from 1 to 6 GHz

frequency.

20

Figure 2.6: Equivalent circuit for a PIN diode [46]

Table 2.1: Parameters value of equivalent circuits for PIN Diodes [46]

PIN Diode state Parameter

L (nH) R(ohm) C (pF)

ON 0.45 3.5 -

OFF 0.45 3K 0.08

A. Mikarmali in [9] also proposed that the equivalent circuit for PIN diode is

the same as Figure 2.5 for his proposed antenna. The values of parameters are: L=

0.6nH, RS = RP = 15Kohm and CT= 0.3 pF. After modeling the PIN diode in a

simulation process, the biasing network is designed to supply the specific bias

voltage and current to the PIN diode in fabrication process. The bias networks are

discussed in the following sub-section.

2.5.3 Biasing Circuit

Bias networks are important devices in any active microstrip circuit to supply

the specific bias voltage and current. The bias network can be realized in lumped

form with lumped inductances and capacitances as distributed network [48].

(a) Series Single Pole Single Throw Switches

An example of a simple circuit diagram of series single pole single throw

switches consists of two capacitors and two inductors as shown in Figure 2.7. The

input DC is connected at the positive terminal of PIN diode while the negative

terminal is connected with the ground. When the RF device is connected with direct

current (DC), the present low frequency from DC must be considered in order to

21

prevent signal from DC (low frequency) being interrupted by RF part (high

frequency). It needs the DC to be blocked to avoid DC signal going to RF signal and

RF chock to evade RF signal goes to DC signal. The estimation value of inductor (L)

as a RF chock and capacitor © as a DC block can be made by using equation 2.9 and

2.10 below [13].

23 45 (2.9)

26 76 (2.10)

Where ZL = Inductive resistance (ohm)

ZC = Capacitive resistance (ohm)

L = Inductor (H)

C = Capacitor (F)

f = frequency (Hz)

The DC source that is used in Figure 2.7 is 6 volts with 50 Hz frequency. The

value of inductive resistance (ZL) must be low to allow DC current to pass through

and activate the PIN diode. At point A, the DC signals cannot pass through the

capacitor since the capacitive resistance (ZC) is very high and it has become a DC

open circuit. By viewing from RF signal source that has high frequency, the value of

ZC must be low or become RF short circuit to allow RF signal to pass through the

capacitor from port 1 and forbid the DC signal from going through the Inductor since

it has very high ZL and looks like an open circuit. Table 2.2 shows the realization

about the circuit representation of inductor and capacitor for DC and RF signal.

Table 2.2: Lumped element’s representation in low and high frequency

Inductor (L) Capacitor (C)

DC (low frequency) Short Open

RF (high frequency) Open Short

22

Figure 2.7: Schematic design of Series SPST Switch

(b) Radial Line Stub

Bias networks are important devices in any active microstrip circuit and can

be found in amplifiers, oscillators and frequency multipliers. Radial stubs provide a

well-defined point for radial wave excitation due to their narrow coupling aperture

[48]. Figure 2.8 shows the example of radial line stub that be used as bias network

for biasing a PIN diode. In [49], the author has proposed the radial stubs that can be

operated on broadband to be applied to active devices that operates more than 100

MHz. A bias network consists of a capacitor that acts as a DC block and RF bias line

with radial stub to form a low pass filter in point A. At this point, only a low

frequency from DC source is passing through to activate the PIN diode while it is

blocked by capacitor from interrupting the RF source.

V_DCSRC1Vdc=6 V

LL1

R=L=0.6 nH

LL2

R=L=0.6 nH

CC2C=0.3 pF

CC1C=0.3 pF

PortP2Num=2

PortP1Num=1

DiodeDIODE1

Mode=nonlinearTrise=Temp=Region=Scale=Periph=Area=Model=

A

Figure 2.

2.6 Previous Related Research

The study on reconfigurable antennas has

year by many researchers. Many types and designs of reconfigurable antenna have

been achieved to improve their performance in diversity of frequency, polarization

and radiation pattern. This sub

reconfigurable antenna from a decade ago up until the latest development. Three

parts have been divided to clarify the related work that has been done by previous

researcher in the development of log

periodic antenna and other development of reconfigurable antenna using electronic

devices.

2.6.1 The Log-Periodic Antenna Development

The development of log

pioneered by some researchers in

that, the development of log

increased rapidly. In [51

element patches using log

antenna is designed using the finite

DC block

PIN diode

Figure 2.8: Bias network configuration using radial line stub

Previous Related Research

The study on reconfigurable antennas has received great attention in recent



and radiation pattern. This sub-topic has discussed about the development of the



researcher in the development of log-periodic antenna, the reconfigur


Periodic Antenna Development

The development of log-periodic antenna for broadband application has been

pioneered by some researchers in University of Illinois, USA in 1955 [50

that, the development of log-periodic antenna to improve the bandwid

increased rapidly. In [51], the author has designed a wideband antenna using nine

element patches using log-periodic slotted configuration as shown in Figure 2.9. This

antenna is designed using the finite- difference time domain method (FDTD) and

λ/4

λ/4

Bias DC source DC block

PIN diode

RF line Radial stub

A

RF source

23

Bias network configuration using radial line stub

received great attention in recent



the development of the



periodic antenna, the reconfigurable log-


periodic antenna for broadband application has been

in 1955 [50]. After

periodic antenna to improve the bandwidth has

has designed a wideband antenna using nine-

periodic slotted configuration as shown in Figure 2.9. This

difference time domain method (FDTD) and

24

compared with fabricated results. The result of VSWR between simulated and

measured is shown in Figure 2.10 below. The scaling factor for this antenna is 1.05

and it is designed for frequency range 8-12 GHz which suitable for Ku-band

application. Compared to the antenna design in this project which uses an inset fed

line, this antenna is used a slotted transmission line underneath a layer of substrate.

Figure 2.9: Log-Periodic Slot Antenna Array structure [51]

Figure 2.10: VSWR of Log-Periodic Slot Antenna Array. (Line - measured, dotted

line - computed) [51]

25

The development of log-periodic dipole antenna for UHF application has

been proposed by the authors in [52]. The fractal Koch design was introduced by the

authors to reduce the overall size of the antenna as shown in Figure 2.11. The

antenna was fabricated on FR-4 board where both arms were fabricated on both sides

of substrate. The same idea with the log-periodic patch antenna in this project was by

applying the log-periodic concept to provide the wideband operation. The scaling

factor of this antenna is 1.17 and this antenna can operates from 0.5 GHz to 4.0 GHz

as shown in Figure 2.12.

Figure 2.11: Log-periodic Dipole Fractal Koch Antenna design [52]

Figure 2.12: Return loss of Log-periodic Dipole Fractal Koch Antenna [52]

26

The development of log-periodic antenna for wideband operation is continued

by A. Scheuring in [53]. They have proposed the theoretical and analytical

calculation of log-periodic design in Terahertz operation as shown in Figure 2.13.

They have claimed that the Terahertz operation could be applied for radio astronomy,

spectroscopy and civil security. The proposed antenna composes of six arm log-

periodic dipole antenna that can operate from 2.0 THz until 4 THz as shown in

Figure 2.14. However, for measurement process the authors have developed a large-

scale antenna that operates at Gigahertz operation due to limitation of equipments.

Figure 2.13: The structure of Log-Periodic Terahertz Antenna [53]

Figure 2.14: The simulated return loss of Log-Periodic Terahertz Antenna [53]

27

2.6.2 The Reconfigurable Log-Periodic Antenna Development

A novel reconfigurable low profile log periodic patch array is proposed in [8].

The patches are fed with a modulated meander line through aperture slots. A

wideband mode from 7–10 GHz and three selected narrow band modes at 7.1, 8.2,

and 9.4 GHz are demonstrated. The wideband to narrow band reconfiguration is

realised by bridging the slot aperture, effectively deactivating the corresponding

radiating element. Potentially the proposed method offers a very fine control of a

narrow pass band. The configurability is done by switching off the patch by bridging

the aperture slot. An almost identical measured and simulated result is presented,

thus verifying the proposed concept.

Figure 2.15: Proposed prototype antenna [8]

(a) (b)

Figure 2.16: Measured (a) S-parameter in dB of wideband log periodic antenna and

(b) Efficiency of reconfigurable antenna [8]

28

In [10], the authors have designed a planar log-periodic dipole array that can

be operated from 1 GHz to 4 GHz. The prototype dipole antenna is fabricated on

R04003C substrate where an arm is located on both sides. The PIN diodes switch is

used at both arms for configuration purposes. So, for a single frequency to

reconfigure, two switches are needed for both arms. Hence, this design use a larger

number of PIN diodes for wideband reconfigurable antenna design compared to the

proposed antenna in this thesis.

(a) (b)

Figure 2.17: The structure of reconfigurable LPDA (a) the schematic design and (b)

fabricated proposed antenna [10]

(a) (b)

Figure 2.18: a) Simulated and b) measured return loss response of the reconfigurable

LPDA [10]

29

The authors in [9] proposed a reconfigurable wideband dipole antenna with

the harmonic trap as shown in Figure 2.19. The harmonic trap is used to eliminate

higher order frequency modes to obtain a smooth wideband frequency operation. The

wideband frequency operation is obtained when eight dipoles are arranged in log-

period array formation. Then, the PIN diodes are connected at every single arm and

harmonic traps tune the frequency from wideband to narrowband. Hence, the biggest

number of PIN diode is need for biggest number of dipole.

Figure 2.19: Schematic design of reconfigurable log-periodic dipole antenna with

harmonic trap [9].

The frequency reconfigurable is obtained by switching the PIN diode to ON

or OFF mode to allow certain desired dipole to radiate. The bandwidth of 1:3 is

achieved when all PIN diode is switched to ON mode and three sub bands are

achieved by selecting several groups oh PIN diodes. The measure return loss of the

antenna is shown in Figure 2.20. This design requires large number of PIN diode for

reconfigurable purposes compared to the RLPA design in this project. The largest

number of PIN diode will degrade the performances of antenna. However, a narrow

band could be obtained over a wideband frequency by selecting a group of radiating

elements which is the same idea with the RLPA.

30

Figure 2.20: Measured return loss of reconfigurable log-periodic dipole antenna [9].

2.6.3 Others Development of Reconfigurable Antenna

A pattern and frequency reconfigurable of annular slot antenna has been

proposed by the authors in [42]. The authors have fabricated the antenna on Duroid

substrate while the configurability has been done by using the PIN diode switch. The

antenna consist of a ring slot antenna acting as radiating element while the

transmission line, matching and biasing network was fabricated on another side of

substrate as shown in Figure 2.21. For this antenna, the radial stub and DC line was

used as the biasing network of PIN diode; same as to the RLPA design.

The matching stub was connected to the PIN diode to provide the frequency

reconfigurability by switching ON and OFF. The antenna can operates at 5.2 GHz,

5.8 GHz and 6.4 GHz as shown in Figure 2.22. In order to reconfigure the radiation

pattern, the PIN diode is used to short the annular slot antenna in preselected

positions along the circumference [42]. Hence, it will change the null at the pattern to

provide the tunable pattern.

31

Figure 2.21: The dimension of annular slot antenna design. The feeding line with

the matching stubs is on the bottom and the annular slot antenna is on the top side of

the substrate [42]

Figure 2.22: Simulated and measurement result of reconfigurable annular slot

antenna at three different frequency [42].

32

(a) (b)

Figure 2.23: Radiation pattern of the reconfigurable annular slot antenna (a)

Simulation (b) Measurement [42].

The frequency reconfigurable using wideband monopole antenna has been

proposed in [7] as shown in Figure 2.24. The U-slot fractal Koch is located at the

middle of the antenna to increase the antenna's electrical length for operation at lower

frequency bands [7]. Without increasing the antenna dimension, this technique will

increase the resonance at a lower frequency. The partial ground plane at the back of

the antenna is function to obtain a wideband operation from 2.5 GHz until 6.7 GHz.

This antenna has used a metal bridge to operate as a RF switch in simulation process.

The frequency reconfigurability is obtained when the RF switch is connected at the

slot by switching ON and OFF state at certain group of RF switch as shown in Table

2.3 below.

Table 2.3: The switches' states of U-Koch reconfigurable microstrip antenna [7]

33

Figure 2.24: The structure of U-Koch reconfigurable microstrip antenna [7]

Figure 2.25: The measured return loss of U-Koch reconfigurable microstrip antenna

[7]

The vivaldi antenna was proposed by the authors in [11] to perform a

wideband operation from 2 GHz until 8 GHz. The antenna was fabricated on Taconic

TLY-5 substrate. The Vivaldi antenna that proposed by the authors have a dimension

of an elliptical shape of tappered slot with horizontal radius 20 mm and vertical

radius of 40 mm. The antenna also consist of 2.3mm radius of circular slot stubs

located at the centre of Vivaldi antenna as shown in Figure 2.26. The antenna was

34

fed by a transmission line and terminated with a quarter circle at the end of

transmission line.

(a) (b) (c)

Figure 2.26: Geometry of the reconfigurable Vivaldi antenna: (a) top view, (b) side

view, and (c) bottom view. [11]

In order to perform a frequency reconfigurability, the antenna is integrated

with ring slots to act as a band stop. Hence, several sub-band frequency could be

obtained from wide band operations by connected or disconnected all these ring

slots. The authors was selected three sub-bands which is high band (7.5 GHz), mid

band (5.0 GHz) and low band (2.5 GHz). The measured return loss can be referred to

in Figure 2.27. The similarities of this antenna with RLPA is the frequency selection

from a wideband operation to a narrow band operations. The authors also used a

metal bridge to perform as an ideal PIN diode in simulation process.

Figure 2.27: Measured return loss of reconfigurable Vivaldi antenna for wideband

and sub-band operation [11]

35

Tab

le 2.4

Pre

viou

s re

sear

ches

on

reco

nfig

urab

le a

nten

na

No

Title / Autho

rs

Recon

figu

rable

Typ

es of

Antenna

Ban

dwidth

Gain

Implem

entation

with real

switch

ing

1 Fr

eque

ncy

Rec

onfi

gura

ble

Log

Peri

odic

Pat

ch A

rray

[8]

Freq

uenc

y L

og-P

erio

dic

7-10

GH

z 9-

16 d

Bi

No/

Usi

ng id

eal

case

2 T

he D

esig

n of

Rec

onfi

gura

ble

Plan

ar L

og-P

erio

dic

Dip

ole

Arr

ay

Usi

ng S

witc

hing

Ele

men

ts [1

0]

Freq

uenc

y L

og-P

erio

dic

1-4

GH

z 7-

8 dB

i N

o/U

sing

idea

l

case

3 W

ideb

and

Freq

uenc

y

Rec

onfi

gura

tion

of a

Pri

nted

Log

-

Peri

odic

Dip

ole

Arr

ay [9

]

Freq

uenc

y L

og-P

erio

dic

0.7-

2.7

GH

z N

ot s

tate

d N

o/U

sing

idea

l

case

4 Pa

ttern

and

Fre

quen

cy

Rec

onfi

gura

ble

Ann

ular

Slo

t

Ant

enna

Usi

ng P

IN D

iode

s [4

2]

Freq

uenc

y an

d

Rad

iatio

n

patte

rn

Ann

ular

slo

t

ante

nna

5.2-

6.4

GH

z N

ot s

tate

d Y

es b

y us

ing

PIN

diod

es

5 A

Rec

onfi

gura

ble

U-K

och

Mic

rost

rip

Ant

enna

For

Wir

eles

s

App

licat

ions

[7]

Freq

uenc

y M

onop

ole

Ant

enna

2.4-

6.7

GH

z 5-

6 dB

i Y

es b

y us

ing

RF

ME

MS

36

6 R

econ

figu

rabl

e V

ival

di A

nten

na

[46]

Freq

uenc

y V

ival

di A

nten

na

2-8

GH

z 1.

14-6

.64

dBi

Usi

ng id

eal c

ase

7 Fr

eque

ncy

tuna

ble

mon

opol

e

coup

led

loop

ant

enna

with

broa

dsid

e ra

diat

ion

patte

rn [1

1]

Freq

uenc

y M

onop

ole

Ant

enna

470-

702

MH

z 2.

8 dB

i Y

es b

y us

ing

vara

ctor

dio

de

8 R

econ

figu

rabl

e W

ideb

and

Patc

h

Ant

enna

for C

ogni

tive

Rad

io [1

4]

Freq

uenc

y A

rray

Ant

enna

5-

7 G

Hz

5-8

dBi

Usi

ng P

IN d

iode

37

2.7 Summary

In conclusion, this chapter has explained literature regarding the log-periodic

antenna and the reconfigurable antenna. The basics of the antenna properties such as

radiation pattern, bandwidth, gain and HPBW have also been elaborated. The log-

periodic concept is introduced and explained to get a wideband operation before

integrated with the lumped elements and PIN diodes. Besides, the circuit

representation of PIN diode and its biasing circuit have also been explained for

reconfigurable purposes. Finally, overviews of the previous works have been

presented and discussed in this chapter.

CHAPTER 3

LOG-PERIODIC ANTENNA DESIGN

3.1 Introductions

This chapter presents a project methodology, the steps of designing,

simulation and fabrication of Log-Periodic Wideband Antenna. The project

methodology of reconfigurable antenna is discussed at Chapter 4. The theory of log-

periodic antenna and wideband antenna design has been discussed in Chapter 2. The

antenna is designed from the development of single patch antenna by numerical

method and verified by simulation using Computer Simulation Technology (CST)

software. Then, the antenna is fabricated on FR-4 substrate using wet etching

technique. The parametric study on varying the parameters of antenna is also

discussed in this chapter. This chapter also included the overall designing process of

both log-periodic antenna and its reconfigurable antenna as Figure 3.1 shows the

flow chart of overall project.

39

Start

Literature review on

wideband and

reconfigurable antenna

Design wideband log-

periodic antenna using

CST Software

Desired

result?

Design a lumped element

circuit to represent RF

PIN Diode using CST

Software

Yes

No

A

Simulate RLPA

with PIN Diode

using CST software

Desired

result?

Yes

No

Theoretical calculation

on antenna design

Antenna fabrication

process

Return Loss

measurement

Radiation pattern and

gain measurement

Result analysis and

documentation

End

Yes

40

Figure 3.1 Flow chart of overall process including log-periodic antenna and

reconfigurable antenna

Return Loss

measurement


gain measurement

Result analysis and

documentation

End

A

Antenna Fabrication

Process

Soldering PIN Diode

and lumped component

to the antenna

Testing the antenna

with switching board

and power supply

Antenna’s

working?

?

Yes

No

41

3.2 Project Methodology and Flow Chart of Log-Periodic Antenna Design

The methodology for this part focuses for log-periodic wideband antenna

(LPA) as shown in Figure 3.2. The design methodology for Reconfigurable Log-

Periodic Antenna (RLPA) will be discussed in the next chapter. The methodology of

this part begins with understanding the antenna parameter such as return loss,

radiation pattern, bandwidth and half-power beamwidth (HPBW). Besides, a

literature review of log-periodic antenna is also studied before proceeding to the next

step. After understanding the concept of log-periodic antenna, a single patch antenna

with inset feed technique is designed using Computer Simulation Technology (CST)

software.

The parameters of the antennas are calculated using appropriate equations

that can be obtained in [3-4]. From this single patch antenna, all the parameters are

scaled up with scaling factor (τ) to obtain wide band antenna. The antenna

parameters such as return loss, input impedance, current distribution and radiation

pattern are observed. For RLPA, the switching circuit for active components was

also designed and simulated. This step will be discussed in Chapter 4.

Then, the fabrication process is done using wet etching technique. The

antenna is fabricated on Flame Retardant 4 (FR4) laminate board with dielectric

constant, εr is 4.5 and loss tangent, tan δ is 0.019. Others equipment such as UV unit,

transparency, etching chemical and ferric chloride acid were used during the

fabrication process. In this situation, the etching room needs to be in a dark condition

to make sure that the laminated board is not exposed to UV light. After the

fabrication process, the SMA port is attached to the antenna.

The measurement process such as return loss, received gain and radiation

pattern was done using network analyzer and anechoic chamber. The network

analyser needs to be calibrated before measuring process is done to make sure that

the measured result is accurate. Finally, both simulated and measured results is

compared and analyzed for documentation.

42

Figure 3.2 Flow chart of research methodology for LPA

Start


log-periodic antenna

Design wideband


using CST Software /

optimization

Desired

result?

Antenna fabrication

process

Return Loss

measurement


gain measurement

Result analysis and

documentation

End

A

Yes

No

Design a single patch

using inset feed line

technique

A

43

3.3 Single Patch Antenna Design

The square patch antenna is the basic and the most commonly used for

microstrip antenna. This patch can be used for the simplest and the most demanding

applications. The sizes calculation of square patch is easier rather than other

dimension since the length and width of the antenna are same. The single patch

microstrip antenna as shown in Figure 3.3 has been designed using CST software.

The antenna is fabricated on FR4 board with the relative dielectric constant, r = 4.5,

substrate thickness of 1.6 mm with tangential loss of 0.019.

An inset feed technique is applied in this antenna design to obtain maximum

input impedance matching. The dimension of single patch after optimization is 23

mm and inset fed length is 8.2 mm with optimum area of substrate is 40x40 mm2

where operates at 3.0 GHz. The magnitude of the back lobe can be reduced while it

increased the gain of the antenna by increasing the sizes of ground plane. The

dimension of square patch can be calculated using equations 3.1 until 3.4 below [3-

4].

The type of feeding technique that will be used is the inset feed technique. It

is one of the easiest feeding techniques and it is also easy to control the input

impedance of the antenna. From figure 2.2 (b), the input impedance level of the patch

can be control by adjusting the length of the inset. The calculation of the inset fed is

shown in the equations 3.5 which show the resonant input resistance for the

microstrip patch. L is the length of the patch, lf is the length of the inset, G1 is the

conductance of the microstrip radiator and G12 is the mutual conductance between

the two slots. The conductance of the radiator is calculated using equation 3.6 and

3.7 while the current excited into the microstrip patch, I1 is calculated using equation

3.8. However, the simplest calculation for finding the inset length is proposed in [21]

as shown in the equation 3.9. This equation is valid for dielectric constant, εr from 2

to 10.

44

Figure 3.3 Simulated design of square patch antennas

𝑊 = 𝑐

2𝑓𝑟

2

𝜀𝑟 + 1 (3.1)

𝐿 =𝑐

2𝑓𝑟 𝜀𝑒𝑓𝑓− 2∆𝐿 (3.2)

𝜀𝑒𝑓𝑓 = 𝜀𝑟 + 1

2 +

𝜀𝑟 − 1

2 1 + 12

𝑕

𝑊 −

12 (3.3)

∆𝐿 = 0.412𝑕 𝜀𝑒𝑓𝑓 + 0.3

𝑊𝑕

+ 0.264

𝜀𝑒𝑓𝑓 − 0.258 𝑊𝑕

+ 0.8 (3.4)

𝑅𝑖𝑛 𝑦 = 𝑙𝑓 =1

2(𝐺1±𝐺12 )𝑐𝑜𝑠2

𝜋

𝐿𝑙𝑓 (3.5)

𝐺1 =𝐼1

120𝜋2 (3.6)

L

L

lf

45

𝐼1 = sin

𝑘0

2 cos𝜃

cos 𝜃

2

𝑠𝑖𝑛3𝜋

0

𝜃 𝑑𝜃 (3.7)

𝐺12 =1

120𝜋2

sin 𝑘0𝑊

2 cos 𝜃

cos𝜃

2

𝐽0 𝑘0𝐿 sin𝜃 𝑠𝑖𝑛3𝜋

0

𝜃 𝑑𝜃 (3.8)

𝑙𝑓 = 10−4 0.001699𝜀𝑟7 + 0.13761𝜀𝑟

6 − 6.1783𝜀𝑟5 + 93.187𝜀𝑟

4 − 682.69𝜀𝑟3

+ 62561.9𝜀𝑟2 − 4043𝜀𝑟 + 6697

𝐿

2 (3.9)

Where:

c = speed of light =3x108 m/s

fr = operating frequency

𝜀𝑟 = permittivity of the dielectric

𝜀𝑒𝑓𝑓= effective permittivity

W = patch width

h = thickness of the dielectric

lf = inset fed length

Rin = input impedance

Figure 3.4 shows the input return loss (S11) for single patch antenna at 3.0

GHz. Input return loss requires the lowest value to make sure the maximum power

reflected back is only 10%. The graph reveals that the return loss for this antenna is -

28 dB or 0.2 % power is reflected back. The simple calculation for return loss

conversion is shown as below:

20 log𝛤 = −27 𝑑𝐵

𝛤 = 𝑎𝑛𝑡𝑖𝑙𝑜𝑔 −27

20 = 0.04467

𝑅𝑒𝑓𝑙𝑒𝑐𝑡𝑒𝑑 𝑃𝑜𝑤𝑒𝑟 𝑖𝑛 % = 0.044672 x 100%

𝑅𝑒𝑓𝑙𝑒𝑐𝑡𝑒𝑑 𝑃𝑜𝑤𝑒𝑟 𝑖𝑛 % = 0.2 %

46

Figure 3.4 Return loss of single patch antenna

The 3-D view of the radiation pattern of square patch antenna is shown in

Figure 3.5 where the value of realized gain is 3.139 dB and the total efficiency is -

3.022 dB or around 50 %. The high value of substrate’s tangential loss is possible

factor of degradation of directivity value. Figure 3.6 (a) shows the polar plot of the

radiation pattern in E-plane with 97.1O of 3 dB beam-width while Figure 3.6 (b)

shows the H-plane of the radiation pattern where the 3 dB beam-width approximately

similar value to the E-plane.

Figure 3.5 3-D view radiation pattern of single patch antenna at 3.0 GHz

47

a)

b)

Figure 3.6: (a) Polar plot of radiation pattern at 3.0 GHz in E-plane and (b) Polar

plot of radiation pattern at 3.0 GHz in H-plane for single patch antenna with theta

and phi setup in simulation.

48

3.4 The Design of Log-Periodic Wideband Antenna

The design of LPA is based on a log-periodic structure that is elaborated in

Chapter 2.3. The geometrical structure and detail dimensions of the proposed LPA

structure is shown in Figure 3.7. There are thirteen square patches with inset fed line

which is connected with a log-periodic array formation to a 50 ohm transmission

line in a top layer of substrate. The antenna structure is constructed on a 1.6 mm

thickness of FR-4 substrate which has relative permittivity (εr) of 4.5 and loss

tangent (tan δ) of 0.019. This antenna structure is designed and the performances are

simulated by using Computer Simulation Technology (CST) software and compared

with measured results.

The antenna is designed for frequency reconfigurability and it needs a

wideband frequency range. However, the limitation of this project is the

performances of PIN diode that will be used. The PIN diode Infenion BAR64-02

only can operate with frequencies below 6 GHz. When that frequency is exceeded,

the isolation (S21) of PIN diode is very high and it will effect to the performance of

the antenna. Hence, the antenna is designed for frequency range up to 6 GHz and

the low frequency for the range is decided to limit the bandwidth of the antenna.

The broader bandwidth causes the increase of antenna size. The gain of the log-

periodic antenna is based on the gain of single patch antenna since the log-periodic

antenna allows a single patch radiated in a single frequency. Hence, the gain of the

log-periodic antenna is nearly same with a single antenna. The design descriptions

of this antenna are shown in Table 3.1.

Table 3.1: Design description of log-periodic antenna

Parameter Value

Operating frequency up to 6 GHz

Bandwidth > 70 %

Gain 6-8 dBi

Radiation pattern Directional

Polarization Linear

49

Figure 3.7: Layout of Log-Periodic Antenna

The design principle for log-periodic wideband antenna requires scaling of

dimensions from period to period so that the performance is periodic with the

logarithm of frequency. The patch length (lp), the width (wp) and the inset feed (I)

are related to the scaling factor (τ) by equation 2.6 in Chapter 2. The dimension of

the first patch (higher frequency) is 11.70 mm x 11.70 mm. The space between each

patch is half wavelength apart thus reducing mutual coupling effect. The dimensions

of proposed antenna are as follows: width of patch, wp =11.7mm, inset feed length, lf

=7.7 mm, distance between the patch, Sa = 11.5 mm (all dimension for smaller

patch), length of transmission line, ltx =208 mm, width of substrate, ws = 230 mm,

length of substrate ls =100 mm, thickness of substrate h = 1.6 mm. Figure 3.8 and

table 3.2 shows the dimensions of log-periodic antenna for each patches.

50

Figure 3.8: Dimension of Log-Periodic Antenna

Table 3.2 LPA dimension for each patch.

Patch Antenna Parameter

Patch Size (wp)

in millimeter

(mm)

Inset feed line

(lf) in millimeter

(mm)

Distance

between patch

(Sa) in mm

Frequency in

GigaHertz

(GHz)

1 11.7 4.17 11.5 6.00

2 12.37 4.41 12.85 5.68

3 13.07 4.66 13.58 5.37

4 13.82 4.93 14.35 5.08

5 14.60 5.21 15.17 4.81

6 15.44 5.50 16.04 4.55

7 16.32 5.81 16.95 4.30

8 17.25 6.15 17.92 4.07

9 18.23 6.50 18.94 3.85

10 19.27 6.87 20.02 3.64

11 20.37 7.26 21.16 3.45

12 21.53 7.67 22.37 3.26

13 22.76 8.11 23.64 3.05

51

3.5 Parametric Study of Log-Periodic Antenna

In this section, the parametric studies have been done by adjusting the value

of Tau factor (τ), distance adjacent patch (Sa) and the length of inset feed line (lf).

Even the calculation method has been done to obtain the dimensions of the antenna

(using equation 3.1- 3.9), the parametric study is also used to obtain optimum results

of wideband operation. The parametric studies have been done by using “Parameter

Sweep” function in CST simulation software.

3.5.1 Simulation on Different Distance of Adjacent Patch (Sa)

From the literature review, the distance between two adjacent patches is an

important criteria to obtain good antenna performance. The distance between the

patch will affect the radiation pattern due to the mutual coupling effect. For a normal

patch such as rectangular or square patch, the suitable distance between two patches

is larger than λ/2 of the patch to give a forward fire radiation pattern in addition to

reducing the mutual coupling effect. However, the trade-off of the larger distance is

the increasing size of the antenna.

In the log-periodic case, the sizes of the patches are different as the sizes of

patches are scaled up from the based patches. Therefore, the mutual coupling effect

is low compared to when using a same patch size. However, this situation does not

mean that the distance of adjacent patch can be ignored. The optimum distance could

give better performance in terms of return loss, efficiency and the radiation pattern.

Hence, for this antenna, the parametric study on varying the value of distance

between adjacent patch (Sa) is studied. The value varies from 10.5 mm until 12.5 mm

at the first two patches while the rest is scaled up by factor.

Figure 3.9 and Table 3.3 shows the result of return loss after varying the

parameters. From the result, it revealed that the distance of adjacent patches

significantly affects the input return loss and the bandwidth. The best bandwidth is

achieved when the distance of adjacent patch is 11.5 mm which is 63.14% or from

3.32 GHz to 6.18 GHz while the rest value gives a bandwidth below than 60%.

52

Further analysis shows that when the value of adjacent patch is increased, the total

length of transmission line and the size of the antenna also increased, leading to a

decrease in the efficiency of the antenna. Among the five values that have been

simulated, the distance 11.5 mm between adjacent patches is chosen to use as the

final simulation because it give a wider bandwidth.

Figure 3.9: Result of varying distance of adjacent patch (Sa)

Table 3.3: Result of varying the adjacent patch

Distance of

Adjacent Patch,

Sa (mm)

Low Frequency,

fL (GHz)

High Frequency,

fH (GHz)

Bandwidth (%)

10.5 3.76 5.1 30.60%

11.0 3.42 6.21 59.80%

11.5 3.32 6.18 63.14%

12.0 3.08 5.21 53.17%

12.5 3.07 5.13 51.91%

53

3.5.2 Simulation on Different Length of Inset Feed Line

The inset fed line is a feeding technique that is used in designing the antenna.

It is a simple technique rather than coaxial fed or aperture slot because the

transmission line is fed to the antenna on the same plane to obtain the maximum

matching network. The calculation of inset fed line using equation 3.5 has been done

to obtain the return loss for a single patch antenna. For log-periodic array antenna

that uses an inset feed line as a feeding technique, the optimization is used to get a

good return loss. The value of inset feed line varies from 4.0 mm to 4.3 mm on the

first patch while the other patches is scaled up by factor.

The result of return loss after varying the inset feed line is presented in Figure

3.10 and Table 3.4 shows the summarized result. After optimizing the value from 4.0

mm to 4.3 mm, the return loss and the bandwidth of the antenna does not change

significantly. The bandwidth of the antenna is about 63% after varying the parameter

value. However, a wider bandwidth below -10 dB return loss occurs when the length

of inset feed line is 4.17 mm which is equivalent to 64.11% or operates from 3.30

GHz until 6.20 Ghz.

Figure 3.10: Result of varying the length of inset feed line (lf)

54

Table 3.4: Result of varying the length of inset feed line

Length of inset

feed line (mm)

Low Frequency,

fL (GHz)

High Frequency,

fH (GHz)

Bandwidth (%)

4.00 3.35 6.25 63.38%

4.10 3.34 6.20 62.85%

4.17 3.30 6.20 64.11%

4.20 3.33 6.17 62.65%

4.30 3.32 6.13 62.29%

3.5.3 Simulation on Different Scaling Factor (τ)

After varying the parameters of adjacent distance between the patches and the

length of inset feed line, the last parameter that will be optimized it is the scaling

factor. The log-periodic design is much related to the scaling factor. Referring to the

equation 2.8 in Chapter 2, the dimensions of antenna’s parameter are scaled up based

on the value of scaling factor. Hence, the changing of the scaling factor could affect

the antenna’s performance. For this antenna design, the best performance is when the

return loss is below -10 dB at desired operating frequency. The scaling factor is

sweep from 1.05 until 1.07 to observe minimum return loss and maximum

bandwidth.

Table 3.5 and Figure 3.11 shows the return loss of the antenna after varying

the value of scaling factor. From the results, it revealed that changing the scaling

factor affects the return loss and the bandwidth of the antenna. All the parameters

that are used in designing the antenna are related to the scaling factor. From the

return loss result, it shows that the scaling factor of 1.055 gives a wider bandwidth

compared to other scaling factors which is 74.20%.

55

Table 3.5: Summaries result of varying the scaling factor.

Scaling Factor ,

τ

Low Frequency

(fL)

High Frequency

(fH)

Bandwidth (%)

1.05 3.20 6.17 66.80%

1.055 3.00 6.20 74.20%

1.06 3.28 6.14 63.73%

1.065 3.32 6.10 61.77%

1.07 3.33 6.18 62.82%

Figure 3.11: Result of varying scaling factor (τ)

3.5.4 Parametric Studies Conclusion

From observation, there are some parameters that have a very strong

influence to the resonant frequency and others are not significant. In conclusion, the

parameter of Sa, lf and τ has a very strong influence in the resonant frequency and the

input impedance of the antenna.

56

3.6 Summary

In this chapter, the research flow, design methodology and simulation setup

of Log-Periodic Wideband Antenna has been briefly described. The initial result of

single patch antenna and the design process of the log-periodic wideband antenna are

also presented. In order to get an optimum result in terms of return loss and

bandwidth, a parametric study of varying the adjacent distance between patches, the

length of inset feed line and the scaling factor value are also presented. The

integration of the antenna with the lumped element and PIN diode to perform a

reconfigurable antenna will be discussed in the next chapter.

CHAPTER 4

RECONFIGURABLE LOG-PERIODIC ANTENNA DESIGN

4.1 Introductions

This chapter discusses project methodology, the steps in designing,

simulating and fabrication of Reconfigurable Log-Periodic Antenna. Based on the

design of log-periodic wideband antenna that was discussed in Chapter 3, the antenna

is modified to integrate with PIN diode switch to perform frequency

reconfigurability. The design of biasing circuit is also discussed and was simulated

using Computer Simulation Technology (CST) software.

In the simulation process, the equivalent circuit modeling for PIN diode

switch is designed to predict the performance of PIN diode and reconfigurable

antenna. Hence, this chapter discusses the equivalent circuit modeling for PIN diode

and the biasing circuit that is used in the proposed antenna. Then, the antenna is

fabricated with FR-4 substrate using wet etching technique. The measurement setup

using network analyzer and anechoic chamber is also presented in the last part of this

chapter.

58

4.2 Project Methodology and Flow Chart

The design methodology for Reconfigurable Log-Periodic Antenna is the

same with the Log-Periodic Antenna. The methodology of this project is started by

understanding of the reconfigurable antenna, the RF switches and the effect of

combination between RF switch and the antenna. The revision on biasing circuit,

switching circuit, PIN diode and its equivalent circuit are deeply studied in order to

reveal its effect on the antenna’s performance. Then, the RLPA was designed and

simulated to study the antenna’s performance in terms of return loss, current

distribution, gain and radiation pattern.

When the simulation process shows a good result, the antenna was fabricated

using wet etching technique. The antenna is fabricated on Flame Retardant 4 (FR4)

laminate board with dielectric constant, εr is 4.5 and loss tangent, tan δ is 0.019.

Other equipment such as a UV unit, transparency, etching chemical and ferric

chloride acid were used during the fabrication process. Then, the drilling process is

continued by drilling the hole at transmission line to connect the biasing network at

the back of the antenna. A copper via is placed through each hole and punched using

puncher to ensure that the copper via is stable.

After that, the PIN diodes and capacitors were embedded into the antenna

using soldering tools. After soldering the components together, the multi-meter was

used to check the connectivity of the components and the antenna. After all

fabrication process is done, the measurement process is continued to get results such

as return loss, received gain and radiation pattern. Finally, both simulated and

measured results is compared and analyzed for documentation. The full flow chart on

designing the RLPA is shown in Figure 4.1.

59

Figure 4.1: RLPA design flow chart

Start


reconfigurable

antenna

Design wideband


using CST Software /

optimization

Desired

result?

Design a lumped element

circuit to represent RF

PIN Diode using CST

Software

Return Loss

measurement


gain measurement

Result analysis and

documentation

End

A

Yes

No

A

Simulate RLPA

with PIN Diode

using CST software

Desired

result?

Yes

No

Antenna Fabrication

Process

Soldering PIN Diode

and lumped component

to the antenna

Testing the antenna

with switching board

and power supply

Antenna’s

working?

?

Yes

No

60

4.3 Analysis of PIN Diode Representation

The PIN diode equivalent circuit is an important part in simulation of

reconfigurable antenna to support better results in measurement process which done

by using real PIN diode. The further explanations about PIN diode equivalent circuits

were discussed in Chapter 2. This part elaborates on the PIN diode that used in this

antenna design using Computer Simulation Technology (CST) software. Two types

of PIN diode representation are simulated and discussed which are:

i. PIN Diode Representation using Lumped Element

ii. PIN Diode Representation Using PEC Pad

A single patch antenna was used for simulation of PIN diode representation.

The antenna dimensions are taken from Chapter 3.3 where:

i. Resonant frequency : 3.0 GHz

ii. Patch width / length : 23 mm

iii. Length of transmission line : 19.7 mm

iv. Length of inset fed : 8.2 mm

v. Gap width : 0.7 mm

vi. Height of substrate : 1.6 mm

61

4.3.1 PIN Diode Representation using Lumped Element

Figure 4.2 shows simulation setting of square patch antenna

incorporated with lumped element data to represent a PIN diode in CST

simulation. The PIN diode equivalent circuit is based on Microsemi [47] that

was discussed in Chapter 2. The equivalent circuit of PIN diode for forward

bias consists of a series combination of the series resistance (RS) and a small

Inductance (LS). In CST simulation software, there are two types of circuit

which are RLC-Serial and RLC Parallel as shown in Figure 4.3. Hence, the

RLC-Series circuit has been chosen to be employed with the antenna. The

values of lumped elements in ON and OFF modes [31] are shown in Table

4.1.

(a) (b)

Figure 4.2: (a) PIN diode representation using lumped element in single

patch antenna. (b) Lumped element data in CST.

62

(a)

(b)

Figure 4.3: lumped element circuits that are developed in CST software (a)

RLC-Serial (b) RLC-Parallel.

Table 4.1: The value of lumped elements as a PIN diode

PIN Diode Modes Resistor (Ω) Inductor (H) Capacitor (F)

ON 2.1 4.5 x 10-12

0

OFF 3000 0 3 x 10-9

The return loss of antenna with lumped element as PIN diode

representation is shown in Figure 4.4. In ON mode, the series circuit of

lumped element consists of 3.5 Ω and inductor 4.5 pH is connected with the

transmission line of antenna. The return loss of -42 dB at 3.0 GHz shows that

the signal from Port 1 antenna has passed through the lumped element circuit

to the patch as a radiating element. While very high return loss (-0.5 dB at 3.0

GHz) is evident on OFF state that consists of series circuit of 3.0 kΩ resistor

and 3.0 nF capacitor. This shows that the series circuit has a very high

impedance to block the signal from going the radiating patch.

63

Figure 4.4: Return loss of antenna (lumped element as a PIN diode)

4.3.2 PIN Diode Representation Using PEC Pad

The other type of PIN diode representation in simulation process is

using a PEC pad. It is represented as an open or short of the transmission line

as shown in Figure 4.5. The ON state is represented by presenting the 3mm x

1mm metal stripe and the absence of the metal strip represents the OFF state.

This type is easier than the lumped element circuit because the simulation is

faster and more accurate. This principle of operation has also been used by

other researchers as reported in [7-9].

(a) (b)

Figure 4.5: PIN Diode representation using PEC pad in (a) ON state (b) OFF

state.

64

Figure 4.6 shows the return loss of the single antenna that use PEC

stripe as a PIN diode. The ON state is indicated by presenting the PEC stripe

to allow the signal from port 1 passed through to the radiating element and

the return loss is -28 dB at 3.0 GHz. While the OFF state is indicated by

removing the PEC stripes and the return loss is -0.6 dB at 3.0 GHz.

Figure 4.6: Return loss of antenna. (PEC stripe as a PIN diode)

65

4.4 Analysis of Biasing Circuit Location

Bias networks are important devices in any active microstrip circuit to supply

the specific bias voltage and current. In this project, the antenna uses the radial stub

and DC line as a biasing network for the PIN diode. Further discussion on radial stub

biasing circuit was discussed in Chapter 2. However, choosing a suitable location of

biasing network is a critical decision to make in order to maintain the antenna’s

performance [42]. Three locations of biasing circuit are discussed to activate the PIN

diode, which is:

i. The biasing circuit at the transmission line of patch (Antenna A1)

ii. The biasing circuit at the centre of length of patches (Antenna A2)

iii. The biasing circuit at the back of antenna (Antenna A3)

The single patch antenna was used for simulation of PIN diode

representation. The antenna dimensions are taken from Chapter 3.3 which are:

i. Resonant frequency : 3.0 GHz

ii. Patch width / length : 23 mm

iii. Length of transmission line : 19.7 mm

iv. Length of inset fed : 8.2 mm

v. Gap width : 0.7 mm

vi. Height of substrate : 1.6 mm

vii. Radial stub : 60°

viii. Length of radial stub : 14.0 mm

66

4.4.1 Biasing circuit at the transmission line of patch (Antenna A1)

Figure 4.7 shows the single patch antenna with biasing circuit

consisting of a quarter wave length radial stub and DC line. The biasing

circuit is located in the middle of transmission line in order to study the

effects of current distribution and return loss of antenna. The DC signal is

connected to the positive terminal of PIN diode via the biasing circuit.

Figure 4.7: The structure of Antenna A1

The simulated current distribution of the antenna was presented in

Figure 4.8. From that figure, it shows that the radial stub biasing circuit did

not disrupt the current flow at the transmission line. Hence, it can be

considered that the biasing circuit was not radiated since the maximum

current distribution was observed. Further analysis of the antenna showed that

the return loss is -17.5 dB as shown in Figure 4.9. It revealed that only low

signal transmitting power was reflected back.

Figure 4.8: Current distribution of Antenna A1

67

Figure 4.9: Return loss of Antenna A1

4.4.2 Biasing circuit at the middle of length patches (Antenna A2).

The second configuration of biasing circuit is shown in Figure 4.10

where the biasing circuit is located mid-length (L) of the patch. The theory

about the patch antenna shows that the radiating slot of the square/rectangular

patch is located at the edge width (W) of the patch. The maximum radiation

can be observed at this region while the minimum radiation is at the

lengthwise edge of patch. Hence, in order to reduce the disruption of the

current distribution, the biasing circuit is placed in the middle of patch’s

length.

Figure 4.10: The structure of Antenna A2

W

L

68

Figure 4.11 shows the simulated current distribution of the antenna.

From that figure, it shows that the current distribution at the patch was not

disrupted by the biasing circuit. Hence, it can be considered that the biasing

circuit was not radiated since the maximum current distribution was seen

along the width of patch. Further analysis of the antenna showed that the

return loss is very deep which -21 dB as shown in Figure 4.12 is. It revealed

that only minimum signal transmitting power was reflected back.

Figure 4.11: Current distribution of Antenna A2

Figure 4.12: Return loss of Antenna A2

69

4.4.3 Biasing circuit at the back of antenna (Antenna A3).

The structure on Figure 4.13 shows the third configuration of biasing

circuit on the single patch antenna. The biasing circuit was placed at the back

of the antenna on a different substrate plane and connected to the

transmission line through the copper via. The structure was constructed in

order to form a tidy design and to avoid destruction to the radiation pattern.

(a) (b)

Figure 4.13: The structure of Antenna A3 (a) front view (b) back view

Figure 4.14 (a) and (b) shows the current distribution of the antenna at

front and back view respectively. The maximum current density is shown at

the front radiating elements while very low current density is radiated at the

back of antenna. This radiation might be give effect to the back lobe of the

radiation pattern. However, the antenna still resonates at a frequency of 3.0

GHz with a return loss of -17 dB as shown in Figure 4.15.

70

(a) (b)

Figure 4.14: Current distribution of Antenna 3 (a) front view (b) back view

Figure 4.15: Return loss of Antenna 3

4.4.4 Parametric Studies Conclusion

The parametric studies on the locations of biasing circuit at the

antenna have been discussed. The biasing circuits are proposed to locate at

the transmission line, at the middle of patches and at the back of the antenna.

The return loss and the current distribution of each antenna also presented to

study the effect of the biasing circuit. The antenna with biasing circuit located

at the back has good current distribution compared the others since the

radiation from biasing circuit is not giving effect to the current distribution of

the antenna besides has return loss below that -10 dB. Hence, this

configuration will be use for full design of reconfigurable antenna.

71

4.5 Reconfigurable Log-Periodic Antenna (RLPA) Design

The wideband frequency reconfigurable based on log-periodic antenna has

been discussed in Chapter 2. The Computer Simulation Technology (CST) software

has been used to design the structure and simulate the performance of the antenna.

The geometrical structure and detail dimensions of the proposed RLPA structure are

shown in Figure 4.16 and Figure 4.17 respectively. There are thirteen square patches

with inset fed lines which are connected with a log-periodic array formation to a 50

ohm transmission line on a top layer of substrate. The antenna structure is

constructed on a FR-4 substrate with a thickness of 1.6 mm which has relative

permittivity (εr) of 4.5 and loss tangent (tan δ) of 0.019. The properties of RLPA are

shown in Table 4.2 while Table 4.3 shows the detailed antenna dimensions for each

patch. All the dimensions of the antenna are based on the dimensions of log-

periodic wideband antenna in Chapter 3.

Table 4.2: Reconfigurable log-periodic antenna properties

Parameter Value

Operating frequency up to 6 GHz

Bandwidth > 70 %

Gain 6-8 dBi

Radiation pattern Directional

Polarization Linear

Reconfigure Frequency

Switching RF PIN Diode

72

Table 4.3 The dimensions for each patches of RLPA.

Patch Antenna Parameter

Patch Size

(wp) in mm

Inset feed line

(lf) in mm

Distance

between

patch (Sa) in

mm

Frequency

in (GHz)

Radial

stub (rs)

in mm

1 11.7 4.17 11.5 6.00 7.23

2 12.37 4.41 12.85 5.68 7.64

3 13.07 4.66 13.58 5.37 8.07

4 13.82 4.93 14.35 5.08 8.53

5 14.60 5.21 15.17 4.81 9.02

6 15.44 5.50 16.04 4.55 9.54

7 16.32 5.81 16.95 4.30 10.08

8 17.25 6.15 17.92 4.07 10.66

9 18.23 6.50 18.94 3.85 11.27

10 19.27 6.87 20.02 3.64 11.91

11 20.37 7.26 21.16 3.45 12.59

12 21.53 7.67 22.37 3.26 13.30

13 22.76 8.11 23.64 3.05 14.06

The reconfigurabilty is achieved when the RF PIN diodes are incorporated

with the feeding line which acts as a switch and to control the ON/OFF mode. In

this project, the parametric study about PIN diode representation in simulation over

RLPA also discussed. The PIN diode representation for simulation process is

carried out by representing a PEC stripe and the lumped element circuit similarly as

discussed for single element before this. The antenna performances in term of return

loss and gain are discussed for both configurations. Using the same substrate

material, the biasing circuit consisting of a radial stubs as a bias network is located

underneath the antenna is connected to a power supply to bias the PIN diode.

73

The complete biasing circuitry controls the bias voltage consisting of high

impedance quarter wave lines, radial stubs, biasing pads, current limiting resistor,

and DC power supply. The quarter-wave length radial stub is located at the back of

antenna to connect from PIN diode to the DC and it operates as a RF choke. The

capacitor is also placed on the transmission line before being connected to the SMA

port to block the DC signal from going into the signal generator. The structure of

Antenna A3 is chosen because it is suitable for wideband antenna design which uses

a huge number of patch elements.

The design principle for log-periodic wideband antenna requires scaling of

dimensions from period to period so that the performance is periodic with the

logarithm of frequency. The patch length (lp), the width (wp) and the inset feed (I)

are related to the scaling factor (τ). The dimension of the first patch (higher

frequency) is 11.70 mm x 11.70 mm. The space between each patch is half a

wavelength apart thus giving a forward fire radiation pattern and reducing the

mutual coupling effect. A gap of 0.8 mm in the middle of patch’s transmission line

is where the PIN diode would be positioned. The dimensions of proposed antenna

are as follows: wp=11.7mm, lf=7.7 mm, rs= 7.23 mm (all dimension for smaller

patch), ltx=208 mm, ws= 230 mm, ls=100 mm, h= 3.305 mm, gap= 0.8 mm, and θ =

60°.

74

Figure 4.16: The geometrical structure of reconfigurable log-periodic antenna

Figure 4.17: Design description of reconfigurable log-periodic antenna

75

The proposed antenna has thirteen patches that require thirteen PIN diode

switches. The wideband operation is achieved when all switches are in ON state. By

controlling the switch at the transmission line of patch, the required frequency band

could be achieved. By controlling each patch using PIN diodes, this antenna is able

to tune from wideband range to narrowband based on required frequency. However,

a group of sub-bands are selected as represent a theory of reconfigurable frequency

selection from wideband range. Besides that, the results from group of sub-bands

are easily discussed and compared to each others. The PIN diode switch conditions

are shown in Table 4.4. In the first case, Band 1 is achieved when the diodes D1

until D5 are ON while the rest are in OFF state. Same as in the first case, the D5-D9

and D9-D13 are in ON states to achieve Band 2 and Band 3 respectively. The other

sub-bands might be achieved by controlling other groups of patches.

Table 4.4 Switches’ states at different bands for RLPA

Diode Band 1 Band 2 Band 3 Wideband

D1 – D5 OFF OFF ON ON

D5 – D9 OFF ON OFF ON

D9 – D13 ON OFF OFF ON

Figure 4.18 (a) and (b) shows two configuration of PIN diode representation

in simulation process which uses PEC stripes and lumped element circuit

respectively. For the first configuration, the switch in RF systems is represented by

an open or short of the transmission line. Therefore, a metal stripes with dimensions

of 3 mm x 0.8 mm is located at the transmission line of patch to represent a switch.

Hence, the ON state is represented by the metal stripe and the absence of the metal

stripe represents the OFF state. In the simulation process, the ohmic losses are

assumed to be zero by using the ideal substrate and perfect electric conductor. In

second configuration using lumped element circuit, the gaps at the transmission line

are connected with lumped component based on circuit in Table 4.1. For this

configuration, the simulation process becomes more difficult because it requires

higher mesh cells and longer simulation times. Hence, to reduce the simulation time,

the first configuration is use for other simulations.

76

(a)

(b)

Figure 4.18: Reconfigurable log-periodic antenna design. (a) PEC stripe as a PIN

diode (b) Lumped element circuit as a PIN diode

PEC

Stripe 3 mm

0.8 mm

77

Figure 4.19: Comparison of PIN diode representation for RLPA in wideband

operation

Table 4.5 Performances of antenna using different PIN diode representation

Parameter PEC Stripe Lumped Element

Low Frequency, fL (GHz) 3.07 GHz 2.95 GHz

High Frequency, fH (GHz) 6.2 GHz 6.3 GHz

Bandwidth (%) 71.7 % 77.7 %

Efficiency (%) /

Gain (dB)

at 3 GHz 31.6 % / 4 dB 25.0% / 2.7 dB

at 4 GHz 39.2 % / 4.8dB 37.2% / 4.5 dB

at 5 GHz 52.2 % / 6.9 dB 43.6% / 6.7 dB

at 6 GHz 38.1% / 3.8 dB 27.5% / 2.4 dB

78

4.6 Fabrication Process

The fabrication process is an intermediate process between the simulation and

measurement process. After obtaining such encouraging results in the simulation, the

antenna needs to be fabricated in order to measure the real antenna. The wet etching

technique was used in this process. The fabrication process consists of several steps

and these steps must be done carefully to get optimum results. Table 4.6 shows the

steps of fabrication process.

Table 4.6: Antenna Fabrication Process

No Picture Explanation

1

The design’s layout was carried out from

CST and was printed over transparency. The

substrate that will be used is FR-4 board with

photo resist layer.

2

Then, this layout will expose under ultra

violet (UV) light over FR-4 board. This step

is doing under lightless condition in order to

protect the photo resist layer.

3

After that, the structure is soaked and etched

about 30 seconds with the acid developer to

remove the positive photo resist layer. This

step also is doing under lightless condition.

4

Afterward, to remove the copper layer at

unused region, the structure was etched using

chemical acids. This is the last part of

fabrication processes.

79

5

Then, antenna will be fed using 50 Ohm

SMA connecter. This process involves the

soldering process using soldering tool. The

SMA connector must be connected to the

transmission line and the ground of antenna.

6

The drilling process is continued by drilled

the hole at transmission line to connect the

biasing network at the back of the antenna. A

copper via will be placed for each hole and

punched using puncher to ensure that the

copper via is sturdy in the hole.

7

After that, the PIN diodes and capacitors

were embedded with antenna using soldering

tools. The temperature of soldering must be

referred to datasheet in order to protect the

component was not over heat.

8

After soldering the components, the multi-

meter was use to checking the connectivity of

the components and the antenna.

9

Then, the antenna was connected with

switching circuit and power supply to

activate the PIN diode and enable the

reconfigurable antenna function. The multi-

meter also was used to check the continuity,

voltage, and current flow over PIN diode.

To activate the PIN diodes, +9 volts DC is

applied while 0 volt DC is applied to

deactivate the PIN diode.

80

10

Finally, the reconfigurable antenna is

measured in term of return loss, power

received and radiation pattern.

4.7 Measurement Process

After the fabrication process, the antenna is tested and measured to validate the

simulation results such as return loss, power received by antenna and the radiation

pattern. All measurement processes have been done in P18 and Wireless

Communication Centre, Universiti Teknologi Malaysia using appropriate

equipments.

4.7.1 Input Return Loss Measurement Setup

The equipment that was used in this measurement is Rohde & Schwarz

Network Analyzer that can measure from 9 kHz to 13 GHz. The equipment and the

calibration kit are shown in Figure 4.20. The first step to measure the input return

loss for those antennas is to setup the start and stop the frequency range. Next, the

equipment needs to be calibrated to ensure that the equipment gives precise results or

in other words can reduce uncertainties during the measurement process. The

calibration process is done by using the calibration kit by loading the open, short and

broadband terminator.

81

(a) (b)

Figure 4.20: Return loss measurement setup. (a) Network analyzer (b) Calibration

kit

4.7.2 Radiation Pattern Measurement Setup

The measurement of received gain of the antenna is conducted by comparing

the antenna with the horn antenna as a reference. The set-up in the anechoic chamber

is shown in Figure 4.21 while Figure 4.22 shows the actual picture of anechoic

chamber. The proposed antenna is placed as the antenna under test (AUT) to measure

the receiving power from the horn antenna. The antenna has been measured, and the

power will be received in dBm by varying the frequency range from 2 GHz to 7

GHz. The radiation pattern of the antenna was measured with a 180 degree rotator in

same anechoic chamber at the selected frequency bands in the E-plane and H-plane.

Figure 4.21: Power received and radiation pattern measurement set-up.

82

Figure 4.22: Anechoic chamber

4.8 Summary

In this chapter, the research flow, design methodology and simulation setup

of Reconfigurable Log-Periodic Antenna has been briefly described. Two types of

PIN diode representation in simulation and three locations of biasing circuit have

been studied and discussed. The simulated RLPA and detailed dimension also

presented. All configuration and design of RLPA have been analysed using CST

Microwave Studio software. The result of simulation and measurement will be

discussed and analysed in the next chapter.

CHAPTER 5

RESULT ANALYSIS AND DISCUSSION

5.1 Introductions

The measurement process is very important to validate the simulation result.

This process is conducted after the fabrication process has been completed. In this

chapter, the simulation result for both Log- Periodic Antenna and Reconfigurable

Log-Periodic Antenna is presented in terms of return loss, current distribution,

realized gain and radiation pattern. The measurement results are also presented in

terms of return loss, power received, and radiation pattern. After that, both

simulation and measurement results are compared, analyzed and discussed. The

comparisons between LPA and RLPA in terms of return loss and radiation pattern

are also presented. The measurement of return loss was conducted using network

analyzer within the range of 2 GHz until 7 GHz. The radiation pattern is plotted

based on measurement of power received by the antenna under test in anechoic

chamber room.

84

5.2 Analysis Result and Discussion of Log-Periodic Antenna

The parametric study of Log-Periodic Antenna has been done and presented

in Chapter 4 in term of varying the scaling factor, the distance between patches and

inset feed length to study the behavior of antenna performance so that a good result

in term of return loss and radiation pattern can be acheived. After simulation using

CST software is done, the antenna was fabricated using FR-4 board using wet

etching technique followed by measurement process. In this part, the simulated and

measured results of LPA are analyzed and compared. The photo of fabricated LPA is

shown in Figure 5.1. The overall size of the proposed antenna is 200mm x 100 mm

and thickness of 1.6mm. The measurement is carried out using Rohde and Schwarz

network analyzer while the radiation pattern is measured with 180 degree rotation in

anechoic chamber and plotted using appropriate software.

Figure 5.1: Photo of fabricated LPA

5.2.1 Input Return Loss

Based on simulation of the log-periodic antenna using CST software, the

input return loss of the antenna is below than -10 dB from 3.18 GHz to 6.23 GHz or

bandwidth of 68.52%. The simulation result then validated by comparing with the

measurement results. The measurement of return loss is conducted using Rohde and

Schwarz network analyzer. Figure 5.2 shows the comparison of the simulated and

measured return loss for log-periodic antenna. The measurement result shows a

good agreement between simulation results. The measurement shows that the

85

antenna can operate from 3.16 GHz to 6.3 GHz or 70.37% bandwidth with respect

to the -10dB.

The log-periodic antenna is an antenna that has periodical repetition of their

impedance and geometry with respect to the logarithm of frequency. Hence, each

element on LPA has their periodical impedance and operating frequencies. Figure

5.2 shows that the return loss of the proposed antenna has many ripples of return

loss. It revealed that every single element radiated for each operating frequency and

this situation is suitable for frequency reconfigurable. The desired frequency over

wideband operation can be selected by switching the PIN diode ON or OFF. The

comparison of the simulated and measured return loss for log-periodic wideband

antenna is shown in Table 5.1.

For simulated antenna bandwidth;

𝐵𝑊 = 𝑓ℎ−𝑓𝐿

𝑓ℎ 𝑓𝐿 × 100% =

6.23−3.18

6.23×3.18 × 100% = 68.52%

For measured antenna bandwidth;

𝐵𝑊 = 𝑓ℎ−𝑓𝐿

𝑓ℎ 𝑓𝐿 × 100% =

6.3−3.16

6.3×3.16 × 100% = 70.37%

Figure 5.2: Simulated and measured return loss for LPA

86

Table 5.1 Comparison of frequency bandwidth between simulation and

measurement for LPA.

Parameter Simulation Measurement

Lower Frequency (fL) 3.18 GHz / -10 dB 3.16 GHz / -10 dB

High Frequency (fH) 6.23 GHz / -10 dB 6.30 GHz / -10 dB

Bandwidth (MHz) 3050 MHz 3140 MHz

Bandwidth (%) 68.52 % 70.37 %

5.2.2 Current Distribution

The simulated current distributions of the log-periodic antenna at four

different resonant frequencies are shown in Figure 5.3. At a lower frequency, it can

be observed that the current propagates at the bigger element which confirms that

the antenna is resonating at the appropriate elements. Figure 5.3 (a) shows the

current distribution of the antenna at the bigger elements while Figure 5.3 (b) shows

the current propagating at the middle elements. The current propagation at 5 GHz

and 6 GHz are shown in Figure 5.3 (c) and 5.3 (d) respectively. The mutual

coupling effect at the antenna can be observed by monitoring the current

distribution or surface current. This effect can be reduced by adjusting the distance

between adjacent elements in the antenna design. However, the adjustment of the

distance may reduce the performance of the antenna especially the return loss and

radiation pattern.

87

(a) (b)

(c) (d)

Figure 5.3: Simulated current distribution for LPA at: (a) 3 GHz (b) 4 GHz (c) 5

GHz (d) 6 GHz.

5.2.3 Realized Gain and Power Received

Table 5.2 shows the simulated realized gain, antenna directivity and its

efficiency when operates over a wideband from 3.0 GHz to 6.0 GHz. From the

table, it revealed that the antenna has a high directivity, with an average of 9.0 dBi.

However, the antenna’s efficiency for the antenna is about 0.45 or 45 % on average

where high efficiency occurs at middle of wideband operations. The gain of the

antenna is affected by the efficiency of the antenna. The higher efficiency of the

antenna will result in higher gain. Since the log-periodic technique enables one

patch to radiate at a single frequency, the gain is approximately equal to the single

patch. Besides, the use of substrate FR-4 which has higher losses might lead to

lower efficiency.

88

Table 5.2: Simulated realized gain and efficiency of the LPA

Frequency Realized Gain (dB) Directivity (dBi) Efficiency

3.0 GHz 3.7454 9.34 0.32

3.5 GHz 4.2085 9.38 0.33

4.0 GHz 4.6103 8.95 0.39

4.5 GHz 4.8112 8.44 0.38

5.0 GHz 6.5542 9.64 0.51

5.5 GHz 5.9326 9.69 0.46

6.0 GHz 3.8230 7.57 0.44

The received measured power of LPA is shows in Figure 5.4. The

measurement process are conducted in an anechoic chamber by comparing the LPA

as an antenna under test (AUT) in receiving mode to the horn antenna as a reference

antenna in transmitting mode. The gain of the antenna was 15 dBi over the range of

0.7 GHz to 18 GHz as mention at Appendix C. The power that was received by the

LPA was plotted in the graph. The power received by the LPA is measured in dBm

by varying the frequency range from 2 GHz to 7 GHz. From the comparison of

power in Figure 5.4, the LPA has received power about 8 dB to 10 dB less than a

horn antenna. The gain of the LPA can be calculated by subtracting the horn

antenna’s gain with the LPA’s power received. Hence, the gain of LPA are 5 dB to

7 dB based on these calculation which also used in [52]. This range of gain is

similar to the simulated realized gain in Table 5.2. From the graph also, the received

power has a higher value at lower frequency compared to higher frequency, due to

the cable losses and free space losses.

89

Figure 5.4: Measured received of the LPA and the horn antenna

5.2.4 Radiation Pattern and Half-Power Beam-width

The simulated and measured radiation patterns for Log-Periodic Antenna are

presented in Figure 5.5 until Figure 5.10. The simulated radiation patterns are taken

from CST Microwave Studio while the measurement results are taken from a 180

degree rotator in an anechoic chamber. Three radiations patterns is selected, where

frequency bands are 3.4 GHz, 4.0 GHz, and 5.8 GHz were plotted using

appropriated software to view the pattern in E-plane (co-polar and cross-polar) and

H-plane (co-polar and cross-polar). Figure 5.5 and Figure 5.6 shows the radiation

pattern at 3.4 GHz for simulated and measured respectively. The simulated pattern

shows a low cross polarization with half power beam-width of 50° and 70.8° for E-

plane and H-plane respectively as shown in Table 5.3. The measured radiation

pattern in E-co and H-co plane at 3.4 GHz exhibit a similar pattern with the

simulation. The same pattern between simulated and measured also had shown at

frequencies of 4.0 GHz and 5.8 GHz.

8 dB 10 dB

90

(a)

(b) (c)

Figure 5.5: Simulated radiation pattern of LPA at 3.4 GHz (a) 3-D view. (b) 2-D

view in E-plane. (c) 2-D view in H-plane (solid line = Co-polar; dotted line = Cross-

polar)

(a) (b)

Figure 5.6: Measured radiation pattern of LPA at 3.4 GHz (a) E-plane. (b) H-plane

(solid line = measurement; dotted line = simulation)

91

(a)

(b) (c)


view in E-plane. (c) 2-D view in H-plane plane (solid line = Co-polar; dotted line =

Cross-polar)

(a) (b)



92

(a)

(b) (c)


view in E-plane. (c) 2-D view in H-plane plane (solid line = Co-polar; dotted line =

Cross-polar)

(a) (b)



93

Table 5.3 Half-power beamwidth for Log-Periodic Antenna

Frequency HPBW (E-plane) HPBW (H-plane)

Simulation Measurement Simulation Measurement

3.4 GHz 58° 62° 70.8° 67°

4.0 GHz 69.3° 58° 83° 65°

5.8 GHz 67.2° 72° 58.4° 68°

5.3 Analysis Result of Frequency Reconfigurable Log-Periodic Antenna and

Discussion

Similar to the LPA, the prototype of the RLPA has been fabricated using

conventional photolithography technique. Figure 5.11 shows a photograph of the

fabricated antenna structure with biasing circuit on FR-4 board. In order to validate

the simulation result, the antenna’s measurement and simulation results have been

compared. The result consists of radiation pattern, power received, realized gain and

radiation pattern. The measurement is carried out using Rohde and Schwarz

network analyzer while the radiation pattern is measured with 180 degree rotation in

anechoic chamber and plotted using appropriate software. The measurement result

shows good agreement between simulated results.

Figure 5.11: Photo of Reconfigurable Log-Periodic Antenna

Power supply

Switching circuit

Antenna

RF PIN Diode

94

5.3.1 Return Loss (S11)

Figure 5.12 to 5.14 show the simulated as well as measured return loss

characteristics of the antenna with different band frequencies. The simulated return

loss when ON state is plotted with measurement result is as shown in Figure 5.12. It

shows that the antenna has a good return loss from 3.17 GHz to 6.2 GHz with

bandwidths up to 71.7% and the result agrees with the measurement. The simulated

return loss for all band of RLPA is shown in Figure 5.13. It shows that the antennas

have a good return loss for band 1, band 2 and band 3 which is 27.2%, 27.3% and

26.6% bandwidth respectively. Figure 5.14 shows the measurement result of return

loss for all three bands. It shows that there are some different values of return loss

compared to simulated result but it has approximately the same bandwidth. For band

1 where diode 9 to 13 is switched ON while the rest is OFF, the return loss 4.65-6.1

GHz range is achieved for measurement results. Meanwhile, when the switching

condition is changed to band 2 and band 3, the return loss 3.28-4.5 GHz and 2.94-

3.71 GHz are achieved respectively. From the graph, it shows that the PIN diode

and radial stub’s effect is minimal upon the measurement result. The presence of a

metal pad in simulation is used to represent a PIN diode in measurement. The

complete result of return loss for proposed antenna is shown in Table 5.4.

Figure 5.12 Simulation and measurement return loss of the antenna when all

switches are in ON state.

95

Figure 5.13: Return loss of simulated reconfigurable log-periodic antenna for

different band

Figure 5.14: Return loss of measured reconfigurable log-periodic antenna for

different band

96

Table 5.4: Comparison of return loss between simulation and measurement of

RLPA

Band f1 (GHz) f2 (GHz) BW (MHz) BW

(%)

Band 1 Simulation 4.6 6.0 1400 27.2

Measurement 4.65 6.1 1450 27.2

Band 2 Simulation 3.73 4.9 1170 27.3

Measurement 3.28 4.5 1220 31.7

Band 3 Simulation 3.0 3.91 910 26.6

Measurement 2.94 3.71 770 23.3

Wide

Band

Simulation 3.17 6.2 3030 71.7

Measurement 3.05 6.27 3220 73.6

5.3.2 Current Distribution

Figure 5.15 shows the simulated current distribution of the proposed antenna

for four different resonant frequencies. The current distribution for RLPA was

similar to the current distribution of LPA. Figure 5.15 (a) shows that the current

propagates at bigger elements for low frequency while for mid frequency, the

current propagates at middle group of patches as shown in Figure 5.15 (b). The

current propagation at 5 GHz and 6 GHz are shown in Figure 5.15 (c) and 5.15 (d)

respectively. From the current distribution, the mutual coupling effect can be

controlled by monitoring the current distribution of two adjacent patches. This

effect can be reduced by adjusting the distance between adjacent elements of the

antenna. The larger distance between elements can reduce the mutual coupling

effect but it can also reduce the performance of the antenna in terms of return loss

and radiation pattern.

97

(a) (b)

(c) (d)

Figure 5.15: Simulated current distribution for reconfigurable log-periodic antenna

at: (a) 3 GHz (b) 4 GHz (c) 5 GHz (d) 6 GHz.

5.3.3 Simulated Realized Gain and Power Received Measurement

The simulated realized gain for reconfigurable log-periodic antenna in the

ON state, OFF state and all three cases of reconfigurable are plotted in Figure 5.16.

It is shown that the antenna has a good gain from 3.0 GHz to 6.0 GHz between 4 dB

to 6 dB for each bands. Since the log periodic technique enables one patch to radiate

at a single frequency, hence the gain is approximately equal to the single patch. It is

worth mentioning that the efficiency for this antenna is about 0.4 to 0.6 hence, the

directivity is about 8 dBi to 10 dBi.

98

(a) (b)

Figure 5.16 (a) Simulated realized gain, directivity and efficiency of RLPA. (b)

Simulated realized gain of RLPA in different sub-bands.

The measurement of received gain of RLPA is conducted by comparing the

RLPA antenna with the horn antenna as a reference. The measurement set-up in the

anechoic chamber is same as the radiation pattern setup as discussed in Chapter 4.

The RLPA is placed as the antenna under test (AUT) in ON and OFF mode to

measure its receiving power from the horn antenna as a reference antenna with gain

of 15 dBi over the range from 0.7 GHz until 18 GHz. The antenna has been

measured: the power received in dBm by varying the frequency range from 2 GHz

to 7 GHz.

Figure 5.17 shows the received power from the horn antenna and RLPA in

the ON and OFF mode versus frequency. From the graph, the RLPA received 8dBm

less than power received by a horn antenna. The gain of the RLPA can be calculated

by subtracting the horn antenna’s gain with the RLPA’s power received. Hence, the

gain of RLPA is about 7 dB based on these calculation which also used in [52]. This

range of gain is similar to the simulated realized gain as shown in Figure 5.17. The

same measurement set-up is also used to investigate the received power in different

planes, as shown in Figure 5.18. This shows that the proposed antenna has a higher

cross polarization, since the antenna was designed for linear polarization. From the

graph, the received power has a higher value at lower frequency compared to higher

frequency, due to the cable losses and free space losses.

99

Figure 5.17: Power received for different types of antenna at measurement set-up

(a) (b)

Figure 5.18: Power received of reconfigurable log-periodic antenna (a) E-Plane (b)

H-Plane

8 dBi

8 dBi

100

5.3.4 Radiation Pattern and Half-Power Beam-width

Figure 5.19 to Figure 5.24 shows the simulated and measured radiation

pattern in E-plane and H-plane. The pattern was plotted over a wideband in

frequency 3.4 GHz, 4.0 GHz and 5.8 GHz to study the polarization in co- and cross-

plane. The radiation patterns of the RLPA at the selected frequency bands in the E-

plane and H-plane were measured with a 180 degree rotator in an anechoic

chamber. The simulated radiation pattern at 3.4 GHz shows the HPBW for E-plane

and H-plane are 69.1° and 55.3° respectively. The small value of cross-polarization

revealed that the antenna is operating at linear polarization.

The comparison of a 180 degree radiation pattern between simulation and

measurement is shown in Figure 5.20. As observed, the measured radiation pattern

has a similar pattern with the simulated and has a directional radiation pattern. It

shows that the effect of integration PIN diode with the antenna have a minimal

effect and does not change the radiation pattern. There are limitations for full

measurement of radiation pattern to study the back lobe radition pattern due to lack

of facilities. The simulated and measured radiation pattern for 4.0 GHz and 5.8 GHz

are shown in Figure 5.21 until Figure 5.24 while the HPBW of the antenna is

demonstrated in Table 5.5. The main lobe of radiation patterns are slightly steered

from 0 degree, due to the difference in phase between the higher frequency and

lower frequency.

101

(a)

(b) (c)

Figure 5.19: Simulated radiation pattern of RLPA at 3.4 GHz (a) 3-D view. (b) 2-D


polar)

(a) (b)

Figure 5.20: Measured radiation pattern of RLPA at 3.4 GHz (a) E-plane. (b) H-

plane (solid line = measurement; dotted line = simulation)

102

(a)

(b) (c)



polar)

(a) (b)



103

(a)

(b) (c)



polar)

(a) (b)



104

Table 5.5 Half-power beamwidth for Reconfigurable Log-Periodic Antenna

Frequency HPBW (E-plane) HPBW (H-plane)


3.5 GHz 69.1° 73° 55.3° 69°

4.0 GHz 73.0° 67° 51.8° 67°

5.8 GHz 66.6° 72° 60.2° 70°

5.4 Overall Discussion

The log-periodic and reconfigurable log-periodic antennas were simulated

with CST simulation tools and fabricated using wet etching technique on a FR-4

substrate. The entire antenna was measured to validate the simulation results in terms

of return loss, antenna gain, half-power beam width and the radiation pattern. The

comparison of overall performances in term of frequency, bandwidth, gain and

HPBW between LPA and RLPA are shown in Table 5.6. The development of

wideband antenna using log-periodic technique is achieved with bandwidth of 70.37

% and 73.6 % after the antenna is implementing with RF switch to perform

reconfigurability operations. Three sub bands are selected from reconfigurable

antenna by switching ON or OFF of RF switches to shows the operations of

reconfigurable antenna. However, the antenna could be configured into different sub-

bands or narrowband depending on its application.

The power received of both antennas also done by comparing the antenna to

the horn antenna as a reference antenna. The measured gain of antennas is the

compared to the simulated gain and it shows that good agreement between them. Due

to the facilities limitation, the measurement of radiation pattern is conducted by

taking a 180 degree radiation pattern while ignoring the back lobe of the antenna.

However, a good agreement between measurement and simulation results was

showed in term of return loss, antenna gain and radiation pattern. The results of the

antennas were discussed and plotted in the graph and tables for better viewing.

105

Table 5.6 Comparison of overall performances in term of frequency, bandwidth,

gain and HPBW between LPA and RLPA

Parameters

Log-Periodic Antenna Reconfigurable Log-

Periodic Antenna


Frequency 3.18 GHz –

6.23 GHz

3.16 GHz –

6.30 GHz

3.17 GHz -

6.2 GHz

3.05 GHz -

6.27 GHz

Bandwidth 68.52 % 70.37 % 71.7 % 73.6 %

Gain

3.4 GHz 4.3 dB 6.0 dB 4.6 dB 6.0 dB

4.0 GHz 4.61 dB 5.0 dB 5.1 dB 7.0 dB

5.8 GHz 4.82 dB 6.0 dB 5.6 dB 6.0 dB

HPBW

(E-Plane)

3.4 GHz 58° 62° 69.1° 73°

4.0 GHz 69.3° 58° 73.0° 67°

5.8 GHz 67.2° 72° 66.6° 72°

5.5 Summary

The simulated and measured results of the Log-periodic Wideband Antenna

and Reconfigurable Log-Periodic Antenna have been presented and discussed. The

simulated result such as return loss, current distribution, realized gain and radiation

pattern has been clearly presented. Then, the measurement process has been done to

validate the simulated results and both results have been compared to each other in

terms of return loss, received power and radiation pattern. The simulation process

has been done using CST Microwave studio while the measurement process has been

done by using network analyzer and anechoic chamber. The results show a good

agreement between simulated and measurement values.

CHAPTER 6

CONCLUSION

6.1 Overall Conclusion

The development of a Log-Periodic Antenna (LPA) and Reconfigurable Log-

Periodic Antenna (RLPA) have been presented and discussed including the designing

process, fabrication process until measurement process. The introduction of RLPA

including a literature study on wideband antenna and reconfigurable antenna is also

presented in addition to the significance of the research works such as a recent

problem statement, the essential objectives and the research scopes. These were all

explained in detail.

The successful output from this research work is a result of plentiful literature

review in the particular field in order to have better understanding regarding the

RLPA development. In addition, the concept and the operating behavior of LPA and

RLPA were presented and discussed deeply with the assistance of appropriate figures

and tables. All the antennas have been design using Computer Simulation

Technology (CST) software which has many applications and bring benefits to the

researcher because the performance and characteristic of the antenna can be analyzed

before proceeding to the fabrication process besides reducing time wastage.

107

The design methodology and flow chart of LPA and RLPA were discussed

separately. The detailed dimension of LPA is included during simulation process

with some optimization of some parameter which are the scaling factor, the length of

inset feed line and the distance between adjacent patch, which are simulated in order

to produce a better result. The design of LPA was then integrated with lumped

elements and PIN diode switches to reconfigure the operating frequency from

wideband operation to narrow band operation which is represented by three sub-

bands (Band 1, Band 2 and Band 3). In the simulation process, three methods to

represent the PIN diode which are using lumped element and PEC pad were

discussed with some results. Then, the radial stub and DC line were use as biasing

circuits to bias the PIN diode with some parametric study on the location of biasing

circuit have been made.

The antennas were fabricated using wet etching technique on a FR-4 substrate

with presented details on the fabrication processes. The entire antenna was measured

to validate the simulation results in terms of return loss, antenna gain and the

radiation pattern. The wideband operation over 70% bandwidth and three sub-bands

with bandwidth around 20% has been measured after reconfigurable operation.

However, the antenna could be configured into different sub-bands or narrowband

depending on its application. Due to the limitation, the measurement of radiation

pattern is conducted by taking a 180 degree radiation pattern while ignoring the back

lobe of the antenna. However, a good agreement between measurement and

simulation results was showed in term of return loss, antenna gain and radiation

pattern. The results of the antennas were discussed and plotted in the graph and

tables for better viewing.

108

6.2 Key Contribution

The development of Log-Periodic Antenna and Reconfigurable Log-Periodic

Antenna has been studied and their performance is analyzed. After hard work on the

antenna’s development, three key contributions were verified:

1. The performance of wideband log-periodic antenna is improved by

integrating RF switch to have reconfigurability operation.

2. A reconfigurable antenna is design based on real circuit modeling of PIN

diode in simulation process using CST software tools. This contribution is

replacing the other method by using ideal case which the simulation results

are not similar to the measurement results.

3. The integration of wideband antenna with lumped elements and real PIN

diodes switches to develop a reconfigurable antenna with separated biasing

circuit is presented.

6.3 Future Research

The structure of Log-Periodic Antenna and Reconfigurable Log-Periodic

Antenna can be improved by the following:

1. One of the limitations of this project is that the PIN diode can be operated up

to a maximum of 6 GHz frequency. The use of high-frequency PIN diodes

could be applied for future research. Hence, the antenna can operate at a

very wideband operation.

2. Using a different substrate material that has a lower loss and higher

dielectric constant which can produce better performance.

3. Different technique of feeding such as aperture slots can be studied to reduce

the effect of PIN diode towards the antenna’s performance. Besides, it might

reduce the size of the antenna.

4. Employ different RF switches (besides PIN diode) without using the biasing

circuit that can disrupt the antenna’s performance.

5. The integration of reconfigurable antenna with FPGA or PIC controller to

automate the switching circuit (smart antenna) can also be studied.

109

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Handbook, Watertown MA: Microsemi Corporation.

48. Gunter Kompa, (2005) Practical Microstrip Design and Application. Artech

House, Norwood.

49. B. A. Syrett, ―A Broad-Band Element for Microstrip Bias or Tuning Circuits‖

IEEE Transactions on Microwaves Theory and Techniques, Vol.MTT-28, No

8, August 1980.

50. R. DuHamel and D. Isbell, ―Broadband Logarithmically Periodic Antenna

Structures,‖ IRE International Convention Record, vol. 5, pp. 119–128, Mar

1957.

115

51. B. L. Ooi, K. Chew, and M. S. Leong ―Log-Periodic Slot Antenna Array‖,

Microwave and Optical Technology Letters, Vol. 25, No. 1, Page: 24-27,

April 5 2000.

52. M. N. A. Karim, M. K. A. Rahim, H. A. Majid, O. Ayop, M. Abu and F.

Zubir, ―Log-Periodic Fractal Koch Antenna for UHF Band Applications‖,

Progress In Electromagnetics Research, PIER 100, 201-218, 2010

53. A. Scheuring, A. Stockhausen, S. Wuensch, K. Ilin, M. Siegel, ―A new

analytical Model for log-periodic Terahertz Antennas‖ European Conference

on Antennas and Propagation (EuCAP), pp. 1-5, 2010

54. M. R. Kamarudin and P. S. Hall, ―Switched Beam Antenna Array with

Parasitic Elements‖ Progress In Electromagnetics Research B, Vol. 13, 187-

201, 2009.

116

APPENDIX A

Author’s Publication

Journal

1. M. F. Ismail, M. K. A. Rahim, H. A. Majid, F. Zubir and O. Ayop,

“Wideband Frequency Reconfiguration Using Switchable PIN Diode”

Microwave and Optical Technology Letters, 2011. – Submitted

2. M. F. Ismail, M. K. A. Rahim & H. A. Majid, “A Wideband Frequency

Reconfigurable Log-Periodic” Jurnal Teknologi, 2011. – Submitted.

Paper Conferences

1. M. F. Ismail, M.K.A. Rahim, S.H.S. Ariffin, S.K.S. Yusuf, M.R. Kamarudin,

“Simulation of Reconfigurable Log-Periodic Microstrip Antenna”

International Symposium on Antenna and Propagations (ISAP), Macao

China, 2010.

2. M. F. Ismail, M. K. A. Rahim, F. Zubir, O. Ayop, “Log-Periodic Patch

Antenna with Tunable Frequency” 5th

European Conference on Antenna and

Propagation (EuCAP), Rome Italy, 2011.

3. M. F. Ismail, M. K. A. Rahim, H. A. Majid, “The Investigation of PIN Diode

Switch on Reconfigurable Antenna” IEEE International RF and Microwave

Conference (RFM), Negeri Sembilan, 2011.

117

APPENDIX B

PIN Diode Datasheet – Infineon BAR64

2007-12-111

BAR64...

Silicon PIN Diode• High voltage current controlled RF resistor for RF attenuator and switches

• Frequency range above 1 MHz up to 6 GHz• Very low capacitance at zero volt reverse bias at frequencies above 1 GHz (typ. 0.17 pF)

• Low forward resistance (typ. 2.1 Ω @ 10 mA)• Very low signal distortion• Pb-free (RoHS compliant) package1)

• Qualified according AEC Q101

BAR64-02LRHBAR64-02VBAR64-03W

BAR64-05BAR64-05W

BAR64-06BAR64-06W

BAR64-07BAR64-04BAR64-04W

Type Package Configuration LS(nH) MarkingBAR64-02LRH BAR64-02V BAR64-03W BAR64-04 BAR64-04W BAR64-05 BAR64-05W BAR64-06 BAR64-06W BAR64-07

TSLP-2-7 SC79 SOD323 SOT23 SOT323 SOT23 SOT323 SOT23 SOT323 SOT143

single, leadless single single series series common cathode common cathode common anode common anode parallel pair

0.4 0.6 1.8 1.8 1.4 1.8 1.4 1.8 1.4 2

O O 2 blue PPs PPs PRs PRs PSs PSs PTs

1Pb-containing package may be available upon special request

2007-12-112

BAR64...

Maximum Ratings at TA = 25°C, unless otherwise specifiedParameter Symbol Value UnitDiode reverse voltage VR 150 V

Forward current IF 100 mA

Total power dissipation BAR64-02LRH, TS ≤ 135 °C BAR64-02V, TS ≤ 125 °C BAR64-03W, BAR64-07, TS ≤ 25 °C BAR64-04, -05, -06, TS ≤ 65 °C BAR64-04W, -05W, -06W, TS ≤ 115 °C

Ptot 250250250250250

mW

Junction temperature Tj 150 °C

Operating temperature range Top -55 ... 125

Storage temperature Tstg -55 ... 150

Thermal ResistanceParameter Symbol Value UnitJunction - soldering point1) BAR64-02LRH BAR64-02V, -04W, -05W, -06W BAR64-03W BAR64-04, -05, -06 BAR64-07

RthJS ≤ 60≤ 140≤ 370≤ 340≤ 290

Electrical Characteristics at TA = 25°C, unless otherwise specifiedParameter Symbol Values Unit

min. typ. max.DC CharacteristicsBreakdown voltage I(BR) = 5 µA

V(BR) 150 - - V

Forward voltage IF = 50 mA

VF - - 1.1

1For calculation of RthJA please refer to Application Note Thermal Resistance

2007-12-113

BAR64...

Electrical Characteristics at TA = 25°C, unless otherwise specifiedParameter Symbol Values Unit

min. typ. max.AC CharacteristicsDiode capacitance VR = 20 V, f = 1 MHz VR = 0 V, f = 100 MHz VR = 0 V, f = 1...1.8 GHz, BAR64-02LRH VR = 0 V, f = 1...1.8 GHz, all other

CT ----

0.230.3

0.130.17

0.35

---

pF

Reverse parallel resistance VR = 0 V, f = 100 MHz VR = 0 V, f = 1 GHz VR = 0 V, f = 1.8 GHz

RP ---

1043

---

kΩ

Forward resistance IF = 1 mA, f = 100 MHz IF = 10 mA, f = 100 MHz IF = 100 mA, f = 100 MHz

rf ---

12.52.1

0.85

202.8

1.35

Ω

Charge carrier life time IF = 10 mA, IR = 6 mA, measured at IR = 3 mA, RL = 100 Ω

τ rr - 1550 - ns

I-region width WI - 50 - µmInsertion loss1) IF = 3 mA, f = 1.8 GHz IF = 5 mA, f = 1.8 GHz IF = 10 mA, f = 1.8 GHz

IL ---

0.320.230.16

---

dB

Isolation1) VR = 0 V, f = 0.9 GHz VR = 0 V, f = 1.8 GHz VR = 0 V, f = 2.45 GHz VR = 0 V, f = 5.6 GHz

ISO ----

2217

14.58.5

----

1BAR64-02LRH in series configuration, Z = 50 Ω

2007-12-114

BAR64...

Diode capacitance CT = ƒ (VR)f = Parameter

0 2 4 6 8 10 12 14 16 V 20

VR

0.1

0.2

0.3

0.4

0.5

pF

0.7

CT

1 MHz100 MHz1 GHz1.8 GHz

Reverse parallel resistance RP = ƒ(VR)f = Parameter

0 5 10 15 20 25 30 V 40

VR

-1 10

0 10

1 10

2 10

3 10

4 10

KOhm

Rp

100 MHz1 GHz1.8 GHz

Forward resistance rf = ƒ (IF)f = 100MHz

10 -2 10 -1 10 0 10 1 10 2 mA

IF

-1 10

0 10

1 10

2 10

3 10

Ohm

RF

Forward current IF = ƒ (VF)TA = Parameter

0 0.2 0.4 0.6 0.8 V 1.2

VF

-6 10

-5 10

-4 10

-3 10

-2 10

-1 10

0 10 A

I F

-40 °C25 °C85 °C125 °C

2007-12-115

BAR64...

Intermodulation intercept pointIP3 = ƒ (IF); f = Parameter

10 -1 10 0 10 1 mA

IF

1 10

2 10

dBm

IP3

f=1800MHz f=900MHz

Forward current IF = ƒ (TS)BAR64-02LRH

0 30 60 90 120 °C 165

TS

0

10

20

30

40

50

60

70

80

90

100

mA120

I F

Forward current IF = ƒ (TS)BAR64-02V

0 15 30 45 60 75 90 105 120 °C 150

TS

0

10

20

30

40

50

60

70

80

90

100

mA120

I F

Forward current IF = ƒ (TS)BAR64-04, BAR64-05, BAR64-06

0 15 30 45 60 75 90 105 120 °C 150

TS

0

10

20

30

40

50

60

70

80

90

100

mA120

I F

2007-12-116

BAR64...

Forward current IF = ƒ (TS)BAR64-04W, BAR64-05W, BAR64-06W

0 15 30 45 60 75 90 105 120 °C 150

TS

0

10

20

30

40

50

60

70

80

90

100

mA120

I F

Permissible Puls Load RthJS = ƒ (tp)BAR64-02LRH

10 -6 10 -5 10 -4 10 -3 10 -2 10 0 s

tp

-1 10

0 10

1 10

2 10

K/W

Rth

JS

0.50.20.10.050.020.010.005D = 0

Permissible Pulse LoadIFmax/ IFDC = ƒ (tp) BAR64-02LRH

10 -6 10 -5 10 -4 10 -3 10 -2 10 0 s

tp

0 10

1 10

2 10

-

I Fm

ax/I F

DC

D = 00.0050.010.020.050.10.20.5

2007-12-117

BAR64...

Permissible Puls Load RthJS = ƒ (tp)BAR64-02V

10 -6 10 -5 10 -4 10 -3 10 -2 10 0 s

tp

-1 10

0 10

1 10

2 10

3 10

K/W

Rth

JS

0.50.20.10.050.020.010.005D = 0

Permissible Pulse LoadIFmax/ IFDC = ƒ (tp)BAR64-02V

10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 1 s

tp

0 10

1 10

2 10

-

I Fm

ax /

I FD

C

D = 00.0050.010.020.050.10.20.5

Permissible Puls Load RthJS = ƒ (tp)BAR64-04, BAR64-05, BAR64-06

10 -6 10 -5 10 -4 10 -3 10 -2 10 0 s

tP

-1 10

0 10

1 10

2 10

3 10

K/W

Rth

JS

0.50.20.10.050.020.010.005D = 0

Permissible Pulse LoadIFmax/ IFDC = ƒ (tp)BAR64-04, BAR64-05, BAR64-06

10 -6 10 -5 10 -4 10 -3 10 -2 10 0 s

tP

0 10

1 10

2 10

-

I Fm

ax/I F

DC

D = 00.0050.010.020.050.10.20.5

2007-12-118

BAR64...

Permissible Puls Load RthJS = ƒ (tp)BAR64-04W, BAR64-05W, BAR64-06W

10 -6 10 -5 10 -4 10 -3 10 -2 10 0 s

tP

-1 10

0 10

1 10

2 10

3 10

K/W

Rth

JS

0.50.20.10.050.020.010.005D = 0

Permissible Pulse LoadIFmax/ IFDC = ƒ (tp)BAR64-04W, BAR64-05W, BAR64-06W

10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 1 s

tP

0 10

1 10

2 10

-

I Fm

ax/I F

DC

D = 00.0050.010.020.050.10.20.5

Insertion loss IL = -|S21|2 = ƒ(f)IF = ParameterBAR64-02LRH in series configuration, Z = 50Ω

0 1 2 3 4 GHz 6

f

-0.4

-0.35

-0.3

-0.25

-0.2

-0.15

-0.1

dB

0

|S21

|2

3 mA

5 mA

10 mA

100 mA

Isolation ISO = -|S21|2 = ƒ(f)VR = ParameterBAR64-02LRH in series configuration, Z = 50Ω

0.5 1.5 2.5 3.5 4.5 GHz 6.5

f

-30

-25

-20

-15

-10

dB

0

|S21

|2

0 V1 V10 V

2007-12-119

BAR64...Package SC79

Package Out l ine

Foot Pr int

Marking Layout (Example)

Standard Packing

Reel ø180 mm = 3.000 Pieces/ReelReel ø180 mm = 8.000 Pieces/Reel (2 mm Pitch)Reel ø330 mm = 10.000 Pieces/Reel

±0.1

1.6

0.31

2

markingCathode

0.8 ±0.1

10˚M

AX.

±0.1

1.2

A

±0.05

10˚M

AX.

0.13

A0.2 M

+0.05-0.03

±0.040.55

±0.0

50.

20.35

0.35

1.35

BAR63-02VType code

Cathode markingLaser marking

2

0.66

0.93

0.4

1.33 1.96

8

0.2

Cathodemarking

4

Cathodemarking

Standard Reel with 2 mm Pitch

2005, JuneDate code

2007-12-1110

BAR64...

Date Code marking for discrete packages with one digi t (SCD80, SC79, SC751)) CES-Code

1) New Marking Layout for SC75, implemented at October 2005.

.

Month 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

01 a p A P a p A P a p A P

02 b q B Q b q B Q b q B Q

03 c r C R c r C R c r C R

04 d s D S d s D S d s D S

05 e t E T e t E T e t E T

06 f u F U f u F U f u F U

07 g v G V g v G V g v G V

08 h x H X h x H X h x H X

09 j y J Y j y J Y j y J Y

10 k z K Z k z K Z k z K Z

11 l 2 L 4 l 2 L 4 l 2 L 4

12 n 3 N 5 n 3 N 5 n 3 N 5

2007-12-1111

BAR64...Package SOD323

Package Out l ine

Foot Pr int


Standard Packing

Reel ø180 mm = 3.000 Pieces/ReelReel ø330 mm = 10.000 Pieces/Reel

BAR63-03WType code


0.8

0.8

0.6

1.7

markingCathode

±0.2

2.5

0.25

0.3

1

-0.05

M A

+0.1

+0.2

2

1.25-0.1

+0.05-0.2

1.7

0.3

0.15-0.06+0.1

0±0.05

+0.2

-0.1

A

0.9+0.2-0.1

±0.1

50.

45

0.24

82.

9

1

2

1.350.65Cathode

marking

2007-12-1112

BAR64...Package SOT143

Package Out l ine

Foot Pr int


Standard Packing


RF s 2005, JuneDate code (YM)

BFP181Type code

56

Pin 1

0.8 0.81.20.

91.

10.

9

1.2

0.8

0.8

0.8 -0.05+0.1

1.9

1.7

±0.12.9

+0.1-0.050.4

0.1 MAX.

1 2

34

0.25 M B

±0.11

10˚ M

AX

.

0.15

MIN

.

0.2 AM

2.4

±0.1

5

0.2 10˚ M

AX

.

A

1.3

±0.1

0...8˚

0.08...0.15

2.6

4

3.15Pin 1

8

0.2

1.15

B

Manufacturer

2007-12-1113


Package Out l ine

Foot Pr int


Standard Packing


EH sBCW66Type code

Pin 1

0.80.

90.

91.

3

0.8 1.2

0.25 M B C

1.9

-0.05+0.10.4

±0.12.9

0.95C

B

0...8˚

0.2 A

0.1 MAX.

10˚ M

AX

.

0.08...0.15

1.3

±0.1

10˚ M

AX

.

M

2.4

±0.1

5

±0.11

A

0.15

MIN

.

1)

1) Lead width can be 0.6 max. in dambar area

1 2

3

3.15

4

2.652.13

0.9

8

0.2

1.15Pin 1

Manufacturer

2005, JuneDate code (YM)

2007-12-1114


Package Out l ine

Foot Pr int


Standard Packing


1.25

±0.1

0.1 MAX.

2.1±

0.1

0.15 +0.1-0.05

0.3+0.1

±0.10.9

1 2

3A

±0.22

-0.05

0.650.65

M

3x0.1

0.1

MIN

.

0.1

M0.2 A

0.24

2.15 1.1

8

2.3

Pin 1

Pin 1

2005, JuneDate code (YM)

BCR108WType code

0.6

0.8

1.6

0.65

0.65

Manufacturer

2007-12-1115

BAR64...Package TSLP-2-7

1

2

±0.050.6

1

2

±0.0

50.

65

±0.0

350.

251)

1±0.

05

0.05 MAX.

+0.010.39 -0.03

1) Dimension applies to plated terminal

Cathodemarking

1)±0.0350.5

Bottom viewTop view

Package Out l ine

Foot Pr int


Standard Packing

Reel ø180 mm = 15.000 Pieces/ReelReel ø330 mm = 50.000 Pieces/Reel (optional)

For board assembly information please refer to Infineon website "Packages"

0.450.

275

0.27

50.

3750.

925

Copper Solder mask Stencil apertures

0.35

1

0.6

0.35

0.3

0.76

4

1.16

0.5

Cathodemarking

8

BAR90-02LRHType code


2007-12-1116

BAR64...

Edition 2006-02-01Published byInfineon Technologies AG81726 München, Germany© Infineon Technologies AG 2007.All Rights Reserved. Attention please! The information given in this dokument shall in no event be regarded as a guarantee of conditions or characteristics (Beschaffenheitsgarantie). With respect to anyexamples or hints given herein, any typical values stated herein and/or any informationregarding the application of the device, Infineon Technologies hereby disclaims anyand all warranties and liabilities of any kind, including without limitation warranties of non-infringement of intellectual property rights of any third party. Information For further information on technology, delivery terms and conditions and prices please contact your nearest Infineon Technologies Office (www.infineon.com). Warnings Due to technical requirements components may contain dangerous substances.For information on the types in question please contact your nearest Infineon Technologies Office.Infineon Technologies Components may only be used in life-support devices orsystems with the express written approval of Infineon Technologies, if a failure ofsuch components can reasonably be expected to cause the failure of that life-support device or system, or to affect the safety or effectiveness of that device or system. Life support devices or systems are intended to be implanted in the human body, or to support and/or maintain and sustain and/or protect human life. If they fail,it is reasonable to assume that the health of the user or other persons may be endangered.

High

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•••

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h gain, low VSh

uency Rangenna Factor: (dBi):

imum ContinRadiated Fiern Type: Beamwidth Beamwidth dance:

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gth: h: ht:

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Frequenc Receive a Individua

horizonta Linearly FCC, MI

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ms' Double Rmance over thndling capabt for both im

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Suble Ridge

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1GHz22 to 41.4 to

r: 300 W200 Vdirecti48° 30° 50 Ω1.6:1 (N-Typ¼ - 20

11.0 in5.6 in.9.6 in.3.5 lb. 5.5" x

1GHz to 18it ed (1, 3 and

on)

E and TEMP

Ridge Guide Hhe frequencybility up to 3

mmunity and

PENDIX C

SAS-571e Guide HoGHz - 18 GHz

bility up to 300both immunit

- 18 GHz 44 dB 15 dBi

Watts /m ional

(3.5:1 max)pe, female 0 Thread, fem

n. (27.9 cm) (14.2 cm) (24.4 cm) 's (1.59 kg)

9.6" (13.9cm

8.0 GHz

10 Meter ca

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Horn Antenny range of 1G

300 watts CWemissions te

1 orn Antennz

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FREQUENCY RECONFIGURABLE LOG-PERIODIC ANTENNA ...

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