DESIGN OF A CIRCULAR POLARIZATION MICROSTRIP ANTENNA AT

2.4GHZ

ZURAIDAH BT HARITH

A project report submitted in partial fulfillment

of the requirements for the award of the degree of

Master of Engineering (Electronics and Telecommunication)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

NOVEMBER, 2005

iii

In the loving memory of my father…..

To my beloved family…..

iv

ACKNOWLEDGEMENT

In preparing this thesis, I was in contact with many people, friends and

academicians. They have contributed towards my understanding and thoughts. In

particular, I would like to express my gratitude to my supervisor, Dr. Mohd

Kamal, for encouragement, guidance, and critics. Without his continued support

and interest, this thesis would not have been the same as presented here.

I also would like to extend my sincere appreciation to all my friends

especially Nurul Rodziah, who have provided assistance at various occasions. To

my colleagues who have helped me through out this project, their views and tips

are useful indeed.

Finally, I would like to thank my loving mother and siblings. Their loves,

supports and prayers have given me strength to finish what I have started. Last but

not least, to my late father, who unable to witness this, you will always be in my

heart.

May Allah bless all of you.

v

ABSTRACT

Microstrip patch antennas represent one family of compact antennas that

offer a conformal nature and the capability of ready integration with

communication system’s printed circuitry. In this project, a 2.4 GHz circular

polarization microstrip antenna is designed, constructed and measured. The

microstrip antenna chose is a dual –fed circular polarized microstrip antenna. The

antenna consists of rectangular patch and 3 dB hybrid. The dual – fed circular

polarized microstrip antenna is etched on a FR4 with dielectric substrate of 4.5

with the height of 1.6 mm. Circular polarization is obtained when two orthogonal

modes are equally excited with 90° phase difference between them. Circular

polarization is important because regardless of the receiver orientation, it will

always able receiving a component of the signal. This is due to the resulting wave

having an angular variation.

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ABSTRAK

Antena mikrojalur mewakili salah satu kumpulan antena termampat yang

mempunyai sifat penyesuaian dan kebolehan untuk berintegrasi degan litar

bercetak di dalam sistem komunikasi. Dalam projek ini, antena mikrojalur polarisi

bulat pada frekuensi 2.4 GHz direka, difabrikasi dan diukur. Antena mikrojalur

yang dipilih untuk projek ini ialah antena mikrojalur dua – suapan polarasi bulat.

Antena ini terdiri daripada bahagian segiempat tepat dan 3 dB hibrid. Antena

mikrojalur dua – suapan polarasi bulat difabrikasikan di atas FR4 dengan pemalar

dielektrik 4.5 dan tinggi 1.6 mm. Polarasi bulat diperolehi apabila dua mod

bertentangan diuja bersama dengan 90° perbezaan fasa di antara mereka. Polarasi

bulat sangat penting kerana tidak kira kedudukan antena penerima, ia akan

sentiasa dapat menerima komponen isyarat. Ini kerana, gelombang yang

dihasilkan mempunyai variasi bersudut.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE i

CERTIFICATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF SYMBOLS xiii

1 INTRODUCTION 1

1.1 Introduction 1

1.2 Wireless Local Area Network (WLAN) System 2

1.3 Objective 3

1.4 Scope of work 3

1.5 Outline of thesis 4

1.6 Summary 5

2 MICROSTRIP ANTENNA 6

2.1 Introduction 6

2.2 Antenna properties 10

2.2.1 Radiation pattern 10

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

2.2.2 Return loss 12

2.2.3 Gain 12

2.2.4 Half power beamwidth 13

2.2.5 VSWR 14

2.2.6 Efficiency 14

2.2.7 Bandwidth 14

2.3 Feeding methods 15

2.3.1 Microstrip line feed 16

2.2.2 Coaxial feed 16

2.3.3 Aperture coupled feed 17

2.3.4 Proximity coupled feed 18

2.4 Summary 20

3 MICROSTRIP ANTENNA POLARIZATION 21

3.1 Polarization type 21

3.1.1 Linear polarization 22

3.1.2 Circular polarization 25

3.1.3 Elliptical polarization 28

3.2 Circularly polarized microstrip antenna 29

3.2.1 Dual– fed circular polarization (CP) patch

antenna

31

3.2.2 Singly fed circular patches 32

3.3 Summary 33

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

4 MICROSTRIP DESIGN, SIMULATION AND

FABRICATION

34

4.1 Design of antenna 35

4.2 Microstrip patch design 36

4.2.1 Rectangular patch 37

4.2.2 3 dB hybrid coupler 39

4.3 Feeding methods for the dual –fed CP patch antenna 40

4.4 Simulation 41

4.5 Fabrication process 41

4.5.1 UV exposure 43

4.5.2 Developing 44

4.5.3 Etching 45

4.6 Measurement 45

4.7 Summary 46

5 SIMULATION AND MEASUREMENT RESULTS 47

5.1 Designed antenna 48

5.2 Simulation results 51

5.3 Measurement 57

5.4 Summary 60

6 CONCLUSION 61

6.1 Conclusion 61

6.2 Future work 62

x

TABLE OF CONTENTS

CHAPTER TITLE PAGE

REFERENCES 63

APPENDICE

APPENDIX A Calculation of axial ratio

xi

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Advantages and disadvantages of microstrip antenna 9

2.2 Comparing the different feed techniques 19

4.1 Performance of microstrip antenna 36

5.1 Length and width for the calculated microstrip patch

antenna

48

xii

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Microstrip antenna 7

2.2 Common shapes of microstrip patch elements 7

2.3 Operations of a Microstrip Patch 8

2.4 3D representation of a radiation pattern 11

2.5 Microstrip Line Feed 16

2.6 Coaxial probe feed 17

2.7 Aperture coupled Feed 18

2.8 Proximity – coupled Feed 19

3.1 Linear polarized EM wave 22

3.2 Vertical linear polarization 22

3.3 Horizontal linear polarization 23

3.4 Linear polarization 23

3.5 Circularly polarize EM wave 25

3.6 Left – hand circular polarization 26

3.7 Right – hand circular polarization 26

3.8 Various type of circularly polarized microstrip

antenna

30

3.9 Dual – fed CP patches 31

3.10 Singly fed circular patches 32

4.1 Design methodology 35

4.2 Dual – fed CP patch antenna with 3dB hybrid 37

4.3 Rectangular Patch Antenna 38

4.4 3 dB hybrid coupler 39

4.5 Flow chart for fabrication process 42

xiii

LIST OF FIGURES

FIGURE NO. TITLE PAGE

4.6 UV exposure machine 43

4.7 Developing the antenna 44

4.8 Microwave Test set 45

5.1 Layout of the microstrip patch antenna 47

5.2 Schematic diagram of the antenna 49

5.3 2D view of the microstrip patch antenna 50

5.4 3D view of the microstrip antenna 50

5.5 Return loss of the microstrip patch antenna 51

5.6 VSWR for the antenna 52

5.7 Radiation pattern 53

5.8 Half power beamwidth 54

5.9 Left hand circular polarization 55

5.10 Right hand circular polarization 56

5.11 Axial ratio for the microstrip antenna 57

5.12 Photo of the fabricated microstrip patch antenna 58

5.13 Microwave Test Set 58

5.14 Measurement of the return loss 59

5.15 Comparison between simulation and measurement 59

xiv

LIST OF SYMBOLS

mm - milimeter

dB - decibel

Hz - hertz

K - kilo

d - diameter

h - height

L - length

W - width

Γ - reflection coefficient

Z0 - characteristic impedance

λο - free-space wavelength

rε - dielectric constant of the substrate

t - patch thickness

c - speed of light 3x 10-8 m/s

CHAPTER 1

INTRODUCTION

1.1 Introduction

Microstrip antenna technology began its rapid development in the late

1970s. By the early 1980s basic microstrip antenna elements and arrays were

fairly well establish in term of design and modeling [1]. In the last decades

printed antennas have been largely studied due to their advantages over other

radiating systems, such as light weight, reduced size, low cost, conformability and

possibility of integration with active devices.

Therefore, this project is aimed to design a circularly polarized antenna at

2.4 GHz. The main advantage of using circular polarization is that regardless of

receiver orientation, it will always receive a component of the signal. This is due

to the resulting wave having an angular variation [2].

This microstrip antenna consists of a radiating patch on the dielectric

substrate. There are various shapes that can be used as the radiating patch.

However, for this project, square patch with 3 dB hybrid will be designed. With

dual feeding methods, two orthogonal modes are equally excited with 90° phase

difference

2

between them, thus the antenna will polarize circularly. The microstrip antenna is

simulated and tested using Microwave Office, where electromagnetic analysis

tools will be used.

The designed is fabricated and tested with network analyzer. Both

simulated and measured results will be compared.

1.2 Wireless Local Area Network (WLAN) System

Wireless LAN can be used either to replace wired LAN, or as an extension

of the wired LAN infrastructure. There are in general two types of antennas for

WLAN applications, fixed WLAN base stations or access points, and the other is

for mobile communication terminals.

For base station applications, impedance matching for WLAN bandwidth

should be better than 1.5:1 VSWR or about 14 dB return loss [3], similar to the

cellular system base station. Antenna that capable to excite circular polarization is

very attractive because it can overcome the multipath fading problem, thus

enhance the system performance, especially indoor WLAN operation [3].

Currently, the most commonly used WLAN system is the IEEE 802.11b

system [4]. A key requirement of WLAN system is that it should be low profile,

where it is almost invisible to the user. For this reason, the microstrip patch

antennas are the antennas of choice for WLAN use due to their small real estate

area and the ability to be designed to blend into the surroundings.

3

1.3 Objective

The objective of this project is to design, simulate, and fabricate a circular

polarization microstrip antenna at 2.4 GHz frequency. The microstrip antenna uses

dual feed techniques. The microstrip antenna is then simulated, fabricated and

measured.

1.4 Scope of work

The project started with designing the microstrip antenna. Then, the

microstrip antenna is simulated using the Microwave Office software. After the

simulation, the microstrip antenna is fabricated using FR4, with dielectric constant

(εr) 4.5 and height of 1.6 mm. Finally the microstrip antenna is measured using the

network analyzer and the measured values are compared with the simulated

values.

4

1.5 Outlines of thesis.

The outlines of the thesis are as follows:

Chapter 1: This chapter provides the introduction to the project, objective and

scope of work.

Chapter 2: This chapter covers the literature review on the microstrip antenna,

the antenna properties, and the feeding methods.

Chapter 3: This chapter covers polarization topic, such as linear and circular

polarization. This chapter also covers the available microstrip

antenna that excites circular polarization.

Chapter 4: Chapter 4 consists of the microstrip design, simulation and

fabrication process of the microstrip antenna.

Chapter 5: This chapter provides the results that are obtained from the

simulation as well as from the measurement.

Chapter 6: This chapter gives the conclusion and future work for this project.

5

1.6 Summary

This chapter provides introduction of the project, followed by a brief

explanation about wireless local area network (WLAN). This chapter also covers

the objective of the project, as well as scope of work that involved. Finally, a

summation of each chapter is briefly outlined.

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CHAPTER 6

CONCLUSION

6.1 Conclusion

There is various type of microstrip antenna that is able to excite a circular

polarization. For this project, dual – fed circular polarization microstrip antenna is

chosen. The microstrip antenna is design to operate at 2.4 GHz frequency. The

dual –fed circular polarization microstrip antenna is successfully implemented and

fabricated. The microstrip antenna resonates at 2.47 GHz and gives a good return

loss, which is -23.25 dB. This is a good value because only 0.47 % power is

reflected and 99.53 % power is transmitted. The VSWR of the microstrip antenna

is 1.2:1, which shows that the level of mismatched for the microstrip antenna is

not very high. High VSWR means that the port is not properly matched. The

bandwidth of this microstrip antenna is also good, which is 17.04 % and the

maximum radiation occurs at -40° with gain of 4.28 dB. The microstrip antenna is

said to be circular if the axial ratio is 0 dB. From the calculation of axial ratio,

most of the angles give 0 dB value, thus prove that the microstrip antenna polarize

circularly.

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6.2 Future work

There is various type of antenna that can excite circular polarization. In

dual feed circular polarization, the rectangular patch can be changed to circular

patch. There is also off line feeding method in dual –fed circular polarization

microstrip antenna. Besides dual fed, there is also a singly – fed circular

polarization. Therefore, in future work, different type of circular polarization can

be designed and studied, so that, a comparisons can be made to the antennas, thus

better microstrip antenna that excites circular polarization can be obtained.

The dual – fed circular polarization microstrip antenna can also be

arranged in an array and become the phase array antenna. This phase array

antenna can steer the radiation without physically moving the antenna. This

antenna can be applied to satellite communication. The circular polarization is

particularly desired since the polarization of linear polarized radio wave may be

rotated the signal passes any anomalies (such as Faraday rotation) in the

ionosphere. Furthermore, due to the position of the Earth with respect to the

satellite, geometric differences may vary especially if the satellite appears to move

with respect to the fixed Earth bound station. Circular polarization will keep the

signal constant regardless of these anomalies.

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in wireless / cellular devices. Florida State University: Masters Thesis

64

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