Design of an Ultra Wideband (UWB) Circular Disc Monopole Antenna721168/FULLTEXT01.pdf · 2014-06-03 · Degree project Design of an Ultra Wideband (UWB) Circular Disc Monopole Antenna

Degree project

Design of an Ultra Wideband (UWB) Circular Disc Monopole Antenna

Supervisor: Sven Erik Sandström

School of Computer Science, Physics and Mathematics

Submitted for the Degree of Master in Electrical Engineering Specialization in Signal Processing & Wave

Propagation

Author: Jamshaid Hussain Asif Date: 2012-11-01

Subject: Master Thesis

Level: Second Level

Course code: 5ED06E

i

Acknowledgement

All praises to Almighty Allah, whose enormous blessings give me strengthand make me able to complete this thesis. I would like to express my heartfeltgratitude to my supervisor, Sven-Erik Sandstrom for his guidance, supportand encouragement. He was quite instrumental to my study with all hisinvaluable view points and extra ordinary motivation. I have been higlyinspired by the zeal and enormous depth of knowledge of his field. I hopethat the study will comply with his optimum expectations.I cannot finish without mentioning my parents and my wife, who have beenoffering all round support during the period of my study.

ii

Abstract

My task was to design a circular disc monopole antenna in the Ultraw-ideband range i.e. 3.1 - 10.6 GHz using the ADS (Advanced Design System)package. In order to achieve the desired matching I simulated different sizesof the radiator, feed line and the ground plane of the antenna and observedthe current flow in a circular monopole at different frequencies. I did someminiaturization (circular shape and chopping) of the antenna and observedthe current flow and radiation pattern in 2D and 3D.

CONTENTS iii

Contents

1 Introduction 11.1 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.4 Breakdown of report . . . . . . . . . . . . . . . . . . . . . . . 2

2 Literature review 32.0.1 Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . 32.0.2 Radiation pattern . . . . . . . . . . . . . . . . . . . . . 32.0.3 Gain and Directivity . . . . . . . . . . . . . . . . . . . 32.0.4 Beamwidth and Efficiency . . . . . . . . . . . . . . . . 42.0.5 Requirements for a UWB antenna . . . . . . . . . . . . 42.0.6 Literature for the monopole antenna . . . . . . . . . . 4

3 The circular disc monopole antenna 73.1 Antenna design . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.1.1 Substrate . . . . . . . . . . . . . . . . . . . . . . . . . 73.1.2 Design of the antenna . . . . . . . . . . . . . . . . . . 73.1.3 Feed line . . . . . . . . . . . . . . . . . . . . . . . . . . 83.1.4 Feed gap . . . . . . . . . . . . . . . . . . . . . . . . . . 93.1.5 Ground plane . . . . . . . . . . . . . . . . . . . . . . . 10

3.2 Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.3 Current flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.4 Miniaturization . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.4.1 Current flow on a circular disc . . . . . . . . . . . . . . 153.4.2 Bandwidth of the disc antenna . . . . . . . . . . . . . . 17

3.5 Chopping of the disc . . . . . . . . . . . . . . . . . . . . . . . 193.5.1 Bandwidth after chopping . . . . . . . . . . . . . . . . 21

4 Final design and results 244.1 Final design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244.2 Current distribution . . . . . . . . . . . . . . . . . . . . . . . 244.3 Radiation pattern . . . . . . . . . . . . . . . . . . . . . . . . . 254.4 Gain and directivity . . . . . . . . . . . . . . . . . . . . . . . 274.5 Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

5 Conclusion 29

1 INTRODUCTION 1

Chapter 1

1 Introduction

At present we are witnessing a very rapid growth of wireless communicationsand in this process antennas with extremely large bandwidth are in demand.A range of applications can then be covered with fewer, or preferably, justone antenna. Such an antenna would cover the band from 0.8 to 11 GHz, andinclude all the existing standards: AMPC 800, GSM 900, GSM 1800, PCS1900, WCDMA/UMTS (3 G), U-NII, DECT, WLANs, European Hiper LANI, II, and UWB (3.1-10.6 GHz) [1]. For these systems, Ultrawideband (UWB)technology provides high data rates and short-range wireless communicationsystems, coding for security and low possibility of interception, as well asmultipath rejection and radar applications. This technology uses an ultra-wide bandwidth of 7.5 GHz, in the range 0.3 to 10.6 GHz.

1.1 Purpose

FirstDesign a circular disc monopole antenna in the Ultrawideband rangei.e. 3.1 - 10.6 GHz in Advanced Design System (ADS) 2011.

SecondAchieve miniaturization and observe the current flow and radiationpattern in 2D and 3D.

ThirdCompare performance in terms of the standard antenna parameters.

1.2 Specification

The parameters used in the simulation:

1. Substrate : RO4350B

2. Permittivity : 3.48

3. Loss tangent : 0.004

4. Height : 254 µm

5. Conductivity : 5.8E+007 Siemens/m

1 INTRODUCTION 2

1.3 Methodology

The software that is used for UWB simulation is the Advanced Design System(ADS) 2011.

1.4 Breakdown of report

This report has 5 chapters and begins with an introduction and a statementof the purpose of the thesis. Chapter 2 gives a brief literature review andsome antenna basics. Chapter 3 discusses the circular disc monopole antennaand miniaturization. Chapter 4 describes the final design and results for theUWB circular disc monopole antenna and Chapter 5 gives some concludingremarks.

2 LITERATURE REVIEW 3

Chapter 2

2 Literature review

The basic antenna concepts that need to be considered in an antenna designare described in this chapter. At the same time, the primary requirementsfor a UWB antenna and some general approaches to achieve wide operatingbandwidth are discussed. Also, some classic UWB antenna configurationsare touched upon.

2.0.1 Bandwidth

The bandwidth (BW) is the range of frequencies within which the perfor-mance of the antenna conforms to a specified standard. Generally, in wirelesscommunications, the antenna is required to provide a return loss of less than-10 dB over its bandwidth. In the band there is typically a standing waveratio in the interval (1 < V SWR < 3) [2].

2.0.2 Radiation pattern

The radiation pattern (or antenna pattern) is the representation of the radi-ated field or intensity as a function of spherical angles. The most importantradiation property is the two or three-dimensional distribution of radiatedenergy as a function of the angular direction. An isotropic antenna has equalintensity in all directions and cannot be realized physically. A linearly po-larized antenna is often described in terms of its principle E-field and H-fieldpatterns. The E-field is defined as the plane containing the electric-field vec-tor and the direction of maximum radiation whilst the H-field is defined asthe plane containing the magnetic-field vector and the direction of maximumradiation [2].

2.0.3 Gain and Directivity

The gain of an antenna is defined as the ratio of the intensity transmittedin a direction to the isotropic intensity. The isotropic intensity equals theabsorbed power from the generator divided by 4π [2].

Gain = 4πradiation intensity

total input (accepted) power= 4π

U(θ, π)

Pin

(1)


In the maximum direction one has the directivity,

D0 =Umax

U0

=4πUmax

Prad

(2)

2.0.4 Beamwidth and Efficiency

The beamwidth of a pattern is defined as the angular separation between twopoints at the same level on opposite sides of the pattern maximum. Thereare a number of beamwidths. The most widely used beamwidth is the Half-Power Beamwidth (HPBW). There is a trade-off between the beamwidth ofthe main lobe and the size of the sidelobes. The beamwidth of the mainlobe also describes the capability of the antenna to distinguish between twoadjacent radiating sources or radar targets [2]. The efficiency relates gainand directivity.

2.0.5 Requirements for a UWB antenna

The antenna has a critical function in UWB systems. Large bandwidth is vi-tal to attain good time domain characteristics [3]. For the narrow band case,one has approximately the same performance over the whole bandwidth andthe basic parameters, such as gain and return loss, are essentially constant.In contrast, UWB systems are often used for data transmission and thismeans that a large bandwidth is occupied. The width of the bandpass filterdetermines the impulse response of the channel. Distortion of the receivedwaveform is one of the things that a UWB antenna should avoid [4].

2.0.6 Literature for the monopole antenna

The conventional monopole is a straight wire configuration above a groundplane. It is one of the most widely used antennas for wireless communicationdue to simplicity, low cost, omindirectional radiation and ease of matchingto 50 Ω [2].

A more elaborate design is a monopole in the shape of a disc above a groundplane. The current is mainly distributed along the edge of the disc, whichindicates that the first resonant frequency is associated with the dimensionof the circular disc [5].

Fig. 1 shows the return loss and the bandwidth for an antenna of this type.This confirms the UWB characteristic of the proposed circular disc monopoleantenna. It is seen in Fig. 2 that the resonant frequency decreases when thediameter of the disc is increased [5].


Figure 1: Simulated and measured return loss curves [5].

Figure 2: Simulated return loss curves for different dimensions [5].

Printed monopole antennas (PMAs) can be integrated with printed circuitboards and is an expanding UWB technology. Rectangular monopoles havenarrow bandwidth and high impedance and circular (disc) monopoles aretherefore preferable. When modified the PSMA to semicircular which givesthe high bandwidth for the communication channel. The large bandwidthand low pulse dispersion makes it suitable for UWB applications [6].


Figure 3: a) Typical feed lenght and b) simulated VSWR for a disc monopole[6].

CDM stands for circular disc monopole. In CDM the special structurereduces the spatial volume and miniaturizes the antenna. This study showsthat the CDM is suitable as an UWB antenna. The projected dimensionsare two times larger than the reported CDM antenna while keeping the sameground plane. A height of 1 mm was found to give maximum bandwidth.The bandwidth corresponding to a V SWR < 2 ranges from 1.17 to 12 GHz[7].

3 THE CIRCULAR DISC MONOPOLE ANTENNA 7

Chapter 3

3 The circular disc monopole antenna

When a circular disc with a hole is mounted over a ground plane it will actas a monopole antenna. An increase in the diameter of the disc causes anincrease in the bandwidth of the monopole antenna. An antenna feedlineis attached to the disc and passes through the ground plane. The gain ofa monopole antenna is twice that of the corresponding dipole antenna. Acircular disc monopole antenna is shown Fig. 4.

Figure 4: Circular disc monopole antenna [8].

3.1 Antenna design

The task was to design a circular disc monopole antenna in the ultra wide-band (UWB) range 3.1-10.6 GHz.

3.1.1 Substrate

In the ADS simulation the Roger substrate RO4350B was used. In the sub-strate layers the substrate has Free Space layers on both sides while in theLayout layers the substrate has metallization layers on both sides; cond isfor the radiator and cond2 is for the ground.

3.1.2 Design of the antenna

The UWB range from 3.1 to 10.6 GHz has the centre frequency 6.85 GHz(wavelength 43.8 mm).


The radius of the radiator is equal to λ/4 [8]. The disc has radius r= 10.95mm and Length L= 68.76 mm.

3.1.3 Feed line

The proposed CDM has feedline

• Width (W) =0.54 mm

• Length (L) =15.31 mm

• Height (H) =0.254 mm

• Impedance (Z)=50 Ω

For the length and width, ADS Linecalc produced:

Figure 5: Length and width of the feedline using linecalc.


3.1.4 Feed gap

The VSWR for the feed gaps 0.81, 0.71, 0.64 and 0.21 mm is shown in Figs.6, 7, 8 and 9.

Figure 6: VSWR for a feed gap of 0.81 mm.




Figs. 6, 7, 8 and 9 show that the smallest feedgap produces the bestVSWR.

Figure 9: The VSWR for a feed gap of 0.21 mm is at an acceptable level.

Figs. 6, 7, 8 show a V SWR > 2 which is not acceptable. In Figure 9 theVSWR is well below 2 over a wide range and this is sufficient for the UWBantenna.

3.1.5 Ground plane

The ground plane in Figure 10 is a cond2 layer with width 50 mm and height25 mm.


Figure 10: Layout of the UWB circular disc monopole antenna.

3.2 Bandwidth

The VSWR of the UWB circular disc monopole antenna is below 1.8 for awide band as shown in Figure 9, and generally in the range 1 < V SWR < 3.The bandwidth of the UWB circular disc monopole antenna in this case liesbetween 3.1 and 10.6 GHz.

3.3 Current flow

The current distribution on the UWB CDM at 4.6, 7.7 and 10 GHz is shownin Figs. 11, 12 and 13, respectively. The current is concentrated to the edgesof the antenna.


Figure 11: Current at 4.6 GHz.

Figure 12: Current at 7.7 GHz.


Figure 13: Current at 10 GHz.

The current around the edges is high while the blue color indicates a lowcurrent and this implies that the centre of the disc could be removed.

3.4 Miniaturization

In the first step of miniaturization, a hole with a diameter of 2.5 mm wasintroduced, as shown in the layout of the CDM in Figure 14. In the followingfigures the diameter is increased gradually.

Figure 14: The antenna with a 2.5 mm hole.


Figure 15: The antenna with a 5 mm hole.

Figure 16: The antenna with a 7.5 mm hole.


Figure 17: The antenna with a 10 mm hole.

3.4.1 Current flow on a circular disc

The simulated currents for these geometries are shown in Figs. 18, 19, 20and 21.The result in Figure 18 shows that the hole has little effect on the currentdistribution.

Figure 18: Current flow for an antenna with a 2.5 mm hole.


Increasing the hole to 5 mm as in Figure 19 does not have any major effect.

Figure 19: Current flow for an antenna with a 5 mm hole.

Figure 20: Current flow for an antenna with a 7.5 mm hole.


Figure 21: Current flow for an antenna with a 10 mm hole.

In Figs. 18 and 19 the current flow is not disturbed by the circular holewhile in Figs. 20 and 21 there is an effect.

3.4.2 Bandwidth of the disc antenna

The simulated VSWR for the CDM antenna with a radius of 12.5 mm andan inner circular hole of 2.5, 5, 7.5 and 10 mm is shown in Figs. 22, 23, 24and 25, respectively.In Figure 22 a VSWR below 2 is maintained for the range 3.1 and 10.6 GHz.

Figure 22: Bandwidth of the CDM with a circular hole of 2.5 mm.


The VSWR with a circular hole of 5 mm is shown in Figure 23. The band-width corresponding to V SWR < 2 is still the interval 3.1 - 10.6 GHz.

Figure 23: Bandwidth of the CDM with a circular hole of 5 mm.

A minor deterioration is seen when the hole is increased to 5 mm. Whenthe hole is increased further the VSWR extends well above 2 in the range ofinterest.

Figure 24: VSWR for a 7.5 mm hole.


Figure 25: VSWR for a 10 mm hole.

A circular disc antenna as shown in Figs. 22 and 23 has a VSWR that liesbelow the reference value 2.

3.5 Chopping of the disc

The VSWR for the the 5 mm antenna was below 1.9 so this case was selectedfor a test where the disc is chopped from the top. A piece that is 7, 8, 9 and12.5 mm is chopped off.

Figure 26: The CDM chopped at 7 mm from the top.





Figure 29: The CDM chopped at 12.5 mm from the top.

3.5.1 Bandwidth after chopping

The bandwidth of an antenna is the range of frequencies over which it isfunctional, usually centered on the resonant frequency. The design is basedon the VSWR. The VSWR and bandwidth of the UWB of the circular discmonopole antenna is shown in Figs. 30, 31, 32 and 33.

Figure 30: Bandwidth of the CDM chopped at 7 mm from the top.





Figure 33: Bandwidth of the CDM chopped at 12.5 mm from the top.

The bandwidth appears in the figures and it is clear that only Fig. 30 meetsthe requirement V SWR < 2.

4 FINAL DESIGN AND RESULTS 24

Chapter 4

4 Final design and results

4.1 Final design

This part of the report explains the final layout of the UWB circular discmonopole antenna after chopping. The VSWR (5 mm hole, chopped at7 mm) was below the reference value 2. Figure 34 shows that the CDMantenna is oriented along the x-y plane.

Figure 34: Final layout of a UWB circular disc monopole antenna afterminiaturization.

4.2 Current distribution

The final design was simulated at 4.6 GHz. Figure 35 shows that the currentdistribution is not disturbed by the miniaturization.


Figure 35: Current flow at 4.6 GHz.

4.3 Radiation pattern

The simulated radiation patterns, in 3D polar plots, are presented in dB inFigs. 36, 37 and 38.

Figure 36: Radiation pattern at 4.6 GHz.

Figure 36 shows the lobes in the θ = 90 plane.


Figure 37: Radiation pattern in the plane θ = 90 at 7.2 GHz.

Figure 38: Radiation pattern in the plane θ = 90 at 10 GHz.

The radiation patterns are almost omnidirectional and there is some fre-quency dependence.


4.4 Gain and directivity

The gain and directivity of the UWB circular disc monopole antenna at 4.6GHz is shown in Figure 39.

Figure 39: Gain and directivity at 4.6 GHz.

The elevation diagram for the directivity and the gain is shown for φ = 0.The maximum CDM directivity at 4.6 GHz is 2.71 dB and the maximumgain is 2.44 dB.

4.5 Efficiency

The efficiency is defined as the ratio between the radiated power and thepower delivered to the antenna. Figure 40 shows that the efficiency of theUWB circular disc monopole antenna is around 90% which is acceptable forthis type of antenna.


Figure 40: Efficiency at 4.6 GHz.

Figure 41: Efficiency as a function of frequency.

Figure 41 shows that the efficiency decreases with frequency.

5 CONCLUSION 29

Chapter 5

5 Conclusion

The design of a circular disc monopole as an ultra-wideband antenna forthe 3.1 to 10.6 GHz band has been carried out with the ADS software tool.Designs that allow miniaturization were devised through simulation and ob-servation of the current distribution. Geometries with a hole in the disc andchopped versions of geometries with a hole in the disc were studied. A VSWRbelow 2 is achieved for the UWB band. The proposed CDM antenna has anefficiency of about 90%. The radiation pattern of the proposed antenna ispresented at 4.6, 7.2 and 10 GHz.

REFERENCES 30

References

[1] Z. N. Chen and M. Y. W. Chia, Broadband Planar, John Wiley, Chich-ester, UK, 2006.

[2] C. A. Balanis, Antenna theory, John Wiley, 3rd Edition, 2005.

[3] E. Lim, Z. Wang, C.U. Lei, Y. Wang and K.L. Man,“Ultra widebandantennas past and present”, IAENG International journal of computerscience, Vol 37, Pages 304-314, 2010.

[4] S. Licul, J. A. N. Noronha, W. A. Davis, D. G. Sweeney, C. R. Anderson,and T.M. Bielawa, “A parametric study of time-domain characteristicsof possible UWB antenna architectures,” In Vehicular Technology Con-ference, Blacksburg, 2003, Pages 3110-3114.

[5] J. Liang, C. C. Chiau, X. Chen, and C. G. Parini, “Study of a printedcircular disc monopole antenna for UWB systems,” IEEE Transactionson Antennas and Propagation, Vol 53, Num 11, Pages 3500-3504, Nov.,2005.

[6] K. P. Ray, Y. Ranga, and P. Gabhale, “Printed square monopole antennawith semicircular base for ultra-wide bandwidth,” Electronics Letters,Vol. 43, Num 5, Pages 13-14, 2007.

[7] N. P. Agrawall, G. Kumar, and K. P. Ray, “Wide-band planar monopoleantennas,” IEEE Transactions on Antennas and Propagation, Vol. 46,Num 2, Pages 294-295, 1998.

[8] K.P. Ray, “Design aspects of printed monopole antennas for ultra-wideband applications”, Hindawi Publishing Corporation, International jour-nal of antennas and propagation, Article ID 713858, 2008.

REFERENCES 31

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Design of an Ultra Wideband (UWB) Circular Disc Monopole Antenna721168/FULLTEXT01.pdf · 2014-06-03 · Degree project Design of an Ultra Wideband (UWB) Circular Disc Monopole Antenna

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