Project paper in journal146901-7575-IJET-IJENS

International Journal of Engineering & Technology IJET-IJENS Vol:14 No:01 166

146901-7575-IJET-IJENS © February 2014 IJENS I J E N S

Electronics Research Institute, El-Tahreer St. Dokki, Giza, Egypt Corresponding author: [email protected]

This work was supported by Science and Technology Development

Fund (STDF)), Ministry of scientific research, Egypt.

Tracking System using Fixed Beamwidth Electronics

Scanning Haythem H. Abdullah, Hala A. Elsadek, and Hesham Eldeeb

Abstract— In several applications for tracking systems, the

scanning rate is considered a critical factor. The mechanical

steering appears to be impractical for its slow rate and space

consumption so the need for electronics scanning appears clearly.

But unfortunately, the electronic scanning suffer from beamwidth

broadening and gain variations with steering angles. In this paper,

a fixed beamwidth electronic scanning algorithm is proposed. The

proposed algorithm is based on synthesizing sets of excitation

coefficients to direct the main beam at some scanning angles. The

synthesis takes into consideration the fixation of the beamwidth at

these angles. The main concept is to enlarge the antenna array

aperture size to a predefined optimum value to get a fixed beam in

all the scanning angles. The synthesis of the excitation coefficients

is done using a scheme based on the method of moments due to its

accuracy in solving such problems. The optimum spacing between

elements is determined using the genetic algorithm. One of the

main advantages of the proposed algorithm is the applicability of

synthesizing multibeam antenna array of fixed beamwidths using

the superposition principle. The system is already built and tested

with conventional microstrip antenna array elements where good

tracking results are observed.

Index Term— Genatic alagorithm, Method of Moments,

Electronic scanning.

I. INTRODUCTION

The synthesis of fixed beamwidth scanned antenna arrays

with minimum number of antenna elements is of main concern

in many applications such as Radar systems and Tracking

systems. Some of applications have mechanical steering

systems, where a directive antenna array of a specific beam is

mounted on a mechanical rotating system that directs the array

to any direction keeping its beam unchanged such as rolling

radar [1]. But the rate of direction change of the mechanical

system is slow. The electronic scanning is used when it is

necessary to vary the direction, or rate of change of direction of

the array beam faster than is possible by mechanical movement

of the aperture [2]. But electronic scanned radars suffer from

the beamwidth variations with steering the main beam

direction. The variations in the antenna array beamwidth as a

function of the steering angle results in corresponding gain

variations, and broadening of the main beam beamwidth which

may cause signals from different transmitters to interfere with

the desired transmitter signal. In this paper, it is introduced a

new algorithm based on a combination between the method of

moments (MoM) [3] and the genetic algorithm (GA) [4-7]. The

proposed algorithm is used for the synthesis of scanned linear

antenna arrays, and multi-beam antenna arrays with fixed

minimum beamwidth at any direction with minimum number

of equispaced antenna elements. In this paper, a tracking

system based on fixing the beamwidth when scanning targets is

presented. The paper is organized as follows: section II

explains the problem formulation. In section III, the results and

discussions are introduced. Finally, Section IV presents the

conclusions for this research.

II. PROBLEM FORMULATION

The array factor of a linear antenna array consisting of

isotropic antenna elements positioned symmetrically along

the z-axis as shown in Figure 1 with uniform element

spacing is given by [1];

( ) ∑ ( (

) )

(1)

Where is the excitation coefficient of the element, is

the element spacing, and ⁄ is the free space wave

number. The moment method and the genetic algorithm

(MoM/GA) [9] are utilized to reconstruct new element

locations and excitations that fulfill the required characteristics

in the desired pattern. This synthesis method has shown its

ability of reducing the number of elements for linear arrays

compared to pencil-beam patterns and shaped-beam patterns

[12]. The algorithm is based on solving a system of linear

equations which is written in a matrix form as

(2)

where is the excitation

coefficients vector to be determined. The elements of the

matrix take the form

∫ ( ) ( )

(3)

The main focus is to introduce a scheme for filling the matrix

in order to achieve predetermined beam characteristics.

Each beam characteristic necessitates specific treatment in

filling the matrix .



A. Synthesis of Fixed Beamwidth Scanned Antenna

Arrays

To get a fixed beamwidth using the phase scanned array, the

array effective length should be retain constant at any

direction and equals the array length as illustrated in Figure

2.

( ) (4)

In Eq. (4), keeping the element spacing unchanged, a fixed

array effective length is obtained by increasing the

number of array elements from N to M such that Eq. (4) is

rewritten as follows

( ) ( ) (5)

where is the number of antenna elements required to

synthesize a radiation pattern with a fixed beamwidth within a

specific radiating sector keeping the element spacing

unchanged. By solving Eq. (5) for , is calculated as

( )

( )

( )

( )

( )

( ) (6)

It should be noted that, for a fixed beamwidth scanning

within a sector of width around the broadside direction, the

minimum number of array elements is calculated according to

Eq. (6). Also, it should be noted that, may be less than or

greater than depending on the sector width .

As an example, consider a phase scanned ⁄ Tschebyscheff

array consists of antenna elements with

, and broadside [32]. Figure 3 shows

the variations in the HPBW with changing the steering

direction. It is calculated by steering the ordinary

⁄ Tschebyscheff pattern [10] via phase shifting and then

measuring the . According to Eq. (6), Figure 4 shows the

number of array elements required to synthesize a fixed

beamwidth, at all directions. It is noticed

that, the required number of elements increases rabidly as

the main beam approaches the end fire direction. The proposed

scheme provides scanning and multibeam pattern synthesis

with fixed beamwidth by optimizing the number of elements

M, element spacing d, and the excitation coefficients . The

aforementioned analyses are coded by the team using Matlab

software.

B. Tracking System Block Diagram and

Implementations.

The implemented security system is described in the block

diagram of Figure 5. The system consists of a transceiver

system that transmits a wave in a predefined direction and then

Fig. 2. The geometry of the linear antenna array

Fig. 1. Geometry of a linear array of M elements positioned

along the z-axis [9].

Fig. 3 The variations in the HPBW with the steering directions

for the 20-elements phase scanned λ ⁄ Tschebyscheff pattern

with

Fig. 4. The number of antenna elements required to synthesize a

phase scanned λ ⁄ Tschebyscheff pattern with fixed

beamwidth at all directions with



receives the backscattered signal from that direction. The angle

of transmission and reception is specified in such a way that the

system scan the surrounding space within a sector of right

angle. The sector angle is divided into 18 scanning angles for

testing. By analyzing the backscattered signal, the appearance

and the disappearance of the monitored objects will be

determined by the system.

The block diagram starts by the design of two similar antenna

arrays each of 8 elements. The designed antenna element is the

conventional microstrip antenna [10].

As illustrated in Figure 5, the system block diagram is

divided into two parts; the transmitter part and the receiver part.

The transmitter ends with an antenna array of 8 elements as an

example. Each element is excited via a voltage controlled phase

shifter (VCPS) and a voltage controlled attenuator (VCA). The

operational flow of the system is depicted in Figure 6. The

system starts by initializing the scanning direction by setting

the scanning angle with the starting angle Ө0 which is -450 in

our case. The next step is to generate a wave of frequency f0

which is set in this experiment to 2.4 GHz. Before

transmission, the direction of the transmitting and the receiving

beams must be adjusted to be oriented to the pre-assigned

scanning angle. The adjustment is done via controlling the

voltages of the VCPSs and the VCAs. The transmitter and the

receiver must have the same maximum radiation to ensure

maximum receptions of the object back scattered waves. At the

receiver part, a power detector is utilized to capture the

backscattered wave and transform it into a DC signal that could

be manipulated within the signal processing unit. The captured

signal is stored in a storage memory of a lab top for further data

processing. The scanning processing continues until the whole

scanning sector is completely scanned then the process is

repeated again until the system is off manually.

The RF front end is the main part of the system that controls

the system scanning process.

The phase and amplitude coordinates are stored in the

processing unit. The processing unit is based on the Atmel

8051 microcontroller that can be connected to the PC computer

via the RS232 protocol. In order to input the magnitude and

phase data to the antenna, a digital to analog Converter (DAC)

is required. The IC DAC0808 is a suitable one for our

application. Since we will have a large number of DC signals

for the voltage controlled phase shifters (VCPS) (JSPHS-2484)

and the voltage controlled attenuators (VCA) (ZX73-2500+), it

is required to have an analog multiplexer with N output DC

channels connected to the phase shifter and variable attenuator

of each antenna element. The RF signal is input to an 8 port

equal power divider. Each port connected to the variable

attenuator which is connected to the phase shifter of each

antenna element. In case of increasing the number of the array

elements to perform more precise accuracy of the point

coordinates or increasing the scanning area, the number of

analog multiplexer channels will be increased according to the

number of microstrip transmitted antenna array elements.

The system starting with the RF source that is connected to a

power divider to branch the RF signal into N RF signals, one

for each array element.

The last step is the control of the amplitude and the phase of the

input power to each array element. This control will be done

via both the VCA and the VCPS.

In the receiving part, instead of the PA, low noise amplifiers

are applied to the received signals from each antenna array

element. The received signals are combined using a power

combiner that is connected to a power detector to convert the

received RF power into DC signals that can be treated easily.

Fig. 5 Tracking system block diagram



III. RESULTS AND DISCUSSIONS

In this work, the scanning sector is chosen such that

( ), where the main beam at is

required to have a beam width close to the broadside main

beam at . Using Eq. (6), the minimum number of

elements required for array synthesis is found to be

with optimum element spacing . The synthesized

pattern has the same beamwidth as the broadside beamwidth

and acceptable side lobe level as shown in

Figure 8 in the broadside direction while it approaches -10.2 dB

at an angle of as illustrated in Figure 9.

Start

Generate signal at

frequency f0

Direct the beam of

the transmitter

toward Direction ӨN

Direct the beam of

the receiver toward

Direction ӨN

Detect the signal

level at direction ӨN

Store the signal level

at direction ӨN

ӨN =ӨN-1 + 1

Initialize scanning

direction

ӨN < ӨEND

Get peaks locations

(Target direction)

Fig. 6. Overall system operational flow

Fig. 7. The experimental setup

Fig. 8. The synthesized radiation pattern with 8 elements

antenna array with broadside radiation

Fig. 9. The synthesized radiation pattern with 8 elements

antenna array with maximum radiation at Ө𝑜 with

respect to the array line



System Integration and Testing.

The integrated system is shown in Figure 7, where the two

antenna arrays are fabricated over FR4 substrates of thickness

1.6 mm. the RF front ends of the transmitter and the receiver

are integrated on separate boards. The connection between

boards is done via coaxial cables of bandwidth up to 18 GHz.

The two RF boards are controlled via two control boxes where

each box adjusts the feeding voltages of the attenuators and the

phase shifters. The whole system is controlled via a lab top

through the USB port. Before starting the system, the output

attenuation factor and the phase shifts of each of the RF front

end branches are calibrated by adjusting the control voltage of

each component.

After calibrating the system which is done once at the fixation

process, a metal slab object with dimensions of m2 is

positioned at a distance 2 m from the antenna for testing. The

back scattered signal at each scanning angle is captured using

the power detector. The object is positioned at different angles

from the detecting system. Figure 10 illustrates the detected

voltage level in the receiver side when the object is positioned

at an angle zero from the normal axis of the detecting system. It

is noticed that, the detected power approaches its peak value at

an angle -10 where the object is already exist. The process is

repeated when the object is positioned at an angle -350. Figures

11 illustrate the detected voltages at each scattering angle when

the object is positioned at -350. As in the first case, the system

detects the object at its right position.

IV. CONCLUSION

The theory of fixing the radiating beam width of a linear

antenna array with the change of the scanning angle using the

MoM/GA algorithm is introduced. The MoM is used to

estimate the excitation coefficients of the antenna array while

the GA is used to estimate the optimum element spacing. The

array synthesis with fixed beamwidth is performed with the

minimum number of antenna elements which is much lower

than the required number of elements in case of the ordinary

phased scanning arrays. The proposed algorithm has efficiently

overcome the beamwidth broadening and gain variations with

steering angles in the phase scanned arrays. The proposed

technique can be used when it is necessary to vary the

direction, or rate of change of direction of the array beam faster

than that is possible by the mechanical movement of the

stationary beam arrays. This paper introduces the details of

building a whole security tracking system. The details of each

of the RF components are presented. The system is tested over

a metal object placed at different angles with respect to the

system. The system succeeds in detecting the position of the

target precisely.

REFERENCES [1] B. W. Tietjen, \The rolling radar," 2005 IEEE International Radar

Conference, 16-21, May 9-12, 2005.

[2] M. F. Radford, \Electronically scanned antenna systems," Proceedings of

the Institution of Electrical Engineers, Vol. 125, No. 11, 1100-1112, Nov. 1978.

[3] R. F. Harrington, Field Computation by Moment Methods, IEEE Press,

1993. [4] Y. Rahmat-Samii, and E. Michielssen, Electromagnetic Optimization by

Genetic Algorithms, John Wiley & Sons, Inc., 1999.

[5] H Houck, C. R., J. A. Joines, and M. G. Kay, \A genetic algorithm for function optimization: A matlab implementation,"

http://www.ie.ncsu.edu:80/mirage/GAToolBox/gaot/.

[6] C. K. Ting, \On the mean convergence time of multi-parent genetic algorithms without selection," Advances in Artificial Life, 403-412, 2005,

ISBN 978-3-540-28848-0. [7] R. L. Haupt, and D. H. Werner, Genetic Algorithms in Electromagnetics,

IEEE Press Wiley Interscience, 2007.

[8] R. C. Hansen, Phased Array Antennas, Wiley & Sons, 1998. [9] A. H. Hussein; Abdullah, H. H.; Salem, A. M.; Khamis, S.; Nasr, M.;

"Optimum Design of Linear Antenna Arrays Using a Hybrid MoM/GA

Algorithm," IEEE, Antennas and Wireless Propagation Letters, vol.10,

no., pp.1232-1235, October 2011.

[10] C. A. Balanis, Antenna Theory: Analysis and Design, 3rd Edition, Wiley,

New York, 2005. [11] S. J. Orfanidis, Electromagnetic Waves and Antenna, 2004, Available:

http://www.ece.rutgers.edu/»orfanidi/ewa/.

[12] Y. Liu, Q. H. Liu, and Z. Nie, “Reducing the number of elements in the synthesis of shaped-beam patterns by the forward-backward matrix pencil

method,” IEEE Trans. Antennas Propag., vol. 58, no. 2, pp. 604–608,

Feb. 2010.

Fig. 10. The power detector output voltages at each scattering

angles when the Object at angle -100

Fig. 11. The power detector output voltages at each scattering

angles when the Object at angle -350

http://www.ie.ncsu.edu/mirage/GAToolBox/gaot/

http://www.ece.rutgers.edu/



Dr. Haythem H. Abdullah received a BSc. degree in

Electronics and communication engineering from the

University of Benha, Egypt in 1998 and received his M.Sc.

and Ph.D. degrees from Cairo University in 2003 and 2010,

respectively. His M.Sc. is dedicated in the simulation of the

dispersive materials in the Finite Difference Time Domain

numerical technique and its application to the SAR

calculations within the Human head. The Ph.D. is dedicated on the radar target

identification. He now employed as a researcher at the electronics research

institute (ERI), Giza, Egypt. His current research interests are design and

optimization of microstrip antenna arrays and their

applications.

Dr. Hala Elsadek. is a professor at Microstrip

Department, Electronics Research Institute. She acted as department head from 2008-2012. Dr. Elsadek

graduated from Faculty of Engineering, Ain Shams

University, Cairo, Egypt 1991. Dr. Elsadek had her master degree from University of Gunma, Japan in 1996

while her PhD was through a channel between Cairo

University, Egypt and University of California, Irvine, USA in 2002. Her

research interests are in the field of RF wireless communications,

electromagnetic engineering and microstrip antenna systems. Dr. Elsadek

published three books, lead guest editors in one international journal in antennas and propagation and two patents in wireless communications and

antenna systems. She acts as a single author and as a co-author in more than 90

research papers in highly cited international journals and in proceedings of international conferences in her field, as IEEE Transactions on Antenna and

Propagation, IEEE Antenna and Wireless Propagation Letters, Microwave and

Optical Technology Letters, etc. She is a supervisor on master and PhD theses in different universities in Egypt and abroad (Japan and USA). Dr Elsadek

participates in more than 12 research projects at the national and international

levels as Egypt- NSF-USA joint fund program, Egypt STDF-France IRD joint fund program and the European Committee programs of FP6 and FP7. Her role

is from C-PI to PI. She is an IEEE senior member from 2011. She is awarded

the Egyptian Government Encouragement Prize for Young scientists in Engineering Science and Technology at 2006. She is included in several

biographical indexes all over the world: American Biographical Institute

Inc, Cambridge, England as one of the leading scientists of in 2008 and "Marquis Who's Who" Encyclopedia from 2008- to 2010 as one of the

worldwide scientists who demonstrate outstanding achievements in her field.

Dr. Elsadek is also a reviewer in many international societies in her field as IEEE Antenna and Propagation Society.

Dr. Hehsam Eldeeb is a professor at Computer and

Systems Department, Electronics Research Institute. He

acts as the Institute director from 2012-Now. Andhe was the Computer and System Department head from

2010-2012. Dr. Eldeeb graduated from Faculty of Engineering, Cairo University, and Cairo, Egypt in

1986. He had his master degree from same university in

1989 while his PhD degree was from Gunma University, Japan in 1996. His research interests are in

the field high performance computing systems and virtual reality. Dr. Eldeeb

acts as a single author and as a co-author in more than 50 research papers in highly cited international journals and in proceedings of international

conferences in his field, He is a head & member in more than 20 of national &

international research projects such as: US–Egypt Joint Fund projects, EU

projects and national research projects. He obtained a Patent in Computer &

Communications field from Egypt’s Patent office (2010). Dr Eldeeb is

supervising over 10 Master & PhD theses in high performance computers & Information technology fields. He also participated in composing two books in

computers & information technology fields

Project paper in journal146901-7575-IJET-IJENS

Documents