Design of dual polarized antenna for mobile communication.

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

DESIGN OF DUAL POLARIZED ANTENNA FOR MOBILE COMMUNICATION

This report submitted in accordance with requirement of the Universiti Teknikal Malaysia Melaka (UTeM) for the Bachelor Degree of Engineering Technology

(JTKEK) (Hons.)

by

NOR IZNI BINTI AZIZAN B071110104

920419-02-5082

FACULTY OF ENGINEERING TECHNOLOGY 2015

UNIVERSITI TEKNIKAL

BORANG PENGESAHA

TAJUK: DESIGN OF DUAL POLARIZED

COMMUNICATION

SESI PENGAJIAN: 2014 Saya NOR IZNI BINTI mengaku membenarkan

Teknikal Malaysia Melaka (UTeM) dengan syar 1. Laporan PSM adalah h

2. Perpustakaan Universiti Teknikal M untuk tujuan pengajian

3. Perpustakaan dibenarkan membuat salina pertukaran antara instit

4. **Sila tandakan ( )

SULIT

TERHAD

TIDAK TERHAD

Alamat Tetap:

NO. 99 Taman Dayang, Jalan Air Hangat,

07000 Langkawi, Kedah. Tarikh: ______________

** Jika Laporan PSM ini SULIT berkenaan dengan menyat akan SULIT at au TERHAD.

UNIVERSITI TEKNIKAL M ALAYSIA MELAKA

PENGESAHAN STATUS LAPORAN PROJEK SARJ

DESIGN OF DUAL POLARIZED ANTENNA FOR MOBILE

2014/15 Semester 2 NOR IZNI BINTI AZIZAN

membenarkan Laporan PSM ini disimpan di Perpustakaan U Melaka (UTeM) dengan syarat-syarat kegunaan s

Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salin untuk tujuan pengajian sahaja dengan izin penulis.

Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan pertukaran antara institusi pengajian tinggi.

TIDAK TERHAD

(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia sebagaimana yang termaktub dalam AKTA RAHSIA RASMI 1972)

(Mengandungi maklumat TERHAD yang telah

oleh organisasi/badan di mana penyelidikan dijalankan)

NO. 99 Taman Dayang,

ah.

____________

Disahkan

Cop Rasmi:

Tarikh: _______________________

ULIT at au TERHAD, sil a l ampirkan surat daripada pihak yat akan sekal i sebab dan t empoh l aporan PSM ini perl u

MALAYSIA MELAKA

ARJANA MUDA

ANTENNA FOR MOBILE

M ini disimpan di Perpustakaan Universiti syarat kegunaan seperti berikut:

Melaka dan penulis. narkan membuat salinan laporan PSM ini sebagai bahan

arjah keselamatan gaimana yang termaktub AD yang telah ditentukan ana penyelidikan dijalankan)

Disahkanol eh:

Tarikh: _______________________

pihak berkuasa/ organisasi perl u dikel askan sebagai

FAKULTI TEKNOLOGI

Tel : +606 234 6623 |

Rujukan Kami (Our Ref) : Rujukan Tuan (Your Ref) :

10 DEC 2015 Pustakawan

Perpustakaan UTeM

Universiti Teknikal Malaysia Hang Tuah Jaya,

76100 Durian Tunggal Melaka.

Tuan/Puan,

PENGKELASAN LAP PROJEK SARJANA (TELEKOMUNIKASI)

Sukacita dimaklumkan

“Design of Dual Polarized

dikelaskan sebagai *SULIT tarikh surat ini.

2. Hal ini adalah kerana

OLEH SYARIKAT LUAR DAN HASIL KA Sekian dimaklumkan. Terima kasih.

Yang benar,

________________

Tandatangan dan Cop Penyelia

* Potong yang tidak berkenaan

NOTA: BORANG INI

SULIT DAN TERHAD.

TERHAD, MAKA BORANG

LAPORAN PSM.

FAKULTI TEKNOLOGI KEJURUTERAAN

Tel : +606 234 6623 | Faks : +606 23406526

Malaysia Melaka 76100 Durian Tunggal,

APORAN PSM SEBAGAI SULIT/TERHAD SARJANA MUDA TEKNOLOGI KEJURUTERAAN (

ASI) ): NOR IZNI BINTI AZIZAN

dimaklumkan bahawa Laporan PSM yang tersebut di atas

Polarized Antenna for Mobile Communication

sebagai *SULIT / TERHAD untuk tempoh LIMA (5)

adalah kerana IANYA MERUPAKAN PROJEK YANG OLEH SYARIKAT LUAR DAN HASIL KAJIANNYA ADALAH SULIT Sekian dimaklumkan. Terima kasih.

Tandatangan dan Cop Penyelia

Potong yang tidak berkenaan

INI HANYA DIISI JIKA DIKLASIFIKASIKAN TERHAD. JIKA LAPORAN DIKELASKAN SEBAGAI

BORANG INI TIDAK PERLU DISERTAKAN

SULIT/TERHAD LAPORAN N (ELEKTRONIK

di atas bertajuk

Communication” mohon

(5) tahun dari

YANG DITAJA ANNYA ADALAH SULIT.

ASIKAN SEBAGAI SEBAGAI TIDAK

DECLARATION

I hereby, declared this report entitled “Design of Dual Polarized Antenna for Mobile Communication” is the results of my own research except as cited in

references.

Signature : ……….

Author’s Name : Nor Izni Binti Azizan Date : 26thJanuary 2015

APPROVAL

This report is submitted to the Faculty of Engineering Technology of UTeM as a partial fulfillment of the requirements for the degree of Bachelor of Engineering Technology in Electronics (Telecommunications) (Hons.). The member of the

supervisory is as follow:

……… (Project Supervisor)

ABSTRAK

Projek ini difokuskan kepada mereka bentuk antenna jalur lebar dua polarisasi yang berfungsi pada frekuensi 2.4GHz untuk sistem komunikasi mudah alih. Antena ini direka khas agar boleh menghasilkan dua jenis polarasi iaitu polarisasi mendatar dan juga polarisasi menegak dengan menggunakan dua liang. Motivasi untuk reka bentuk antena ini adalah disebabkan untuk mengurangkan gangguan yang berlaku semasa menghantar dan menerima isyarat kepada dan daripada antena. Gangguan penghantaran isyarat yang sering berlaku disebabkan oleh cuaca dan menjadi kritikal semasa cuaca buruk. Oleh itu, kemahuan ini menyebabkan kelajuan rendah daripada isyarat penghantaran dan tidak memenuhi permintaan pengguna masa kini. Untuk memenuhi syarat ini, antena jalur lebar yang lebih luas diperlukan. Antena dua polarisasi adalah reka bentuk untuk mengurangkan gangguan semasa memancar atau menerima isyarat sebagai jenis dua polarisasi digunakan iaitu polarisasi yang menegak dan polarisasi mendatar. Kepelbagaian polarisasi adalah salah satu teknik yang berguna untuk meningkatkan prestasi antara antena pemancar dan penerima gelombang mikro kerana ia boleh mengurangkan hubungan ruang yang boleh mengurangkan prestasi sistem. Proses reka bentuk boleh dibahagikan kepada dua langkah reka bentuk. Pertama, antena polarisasi dual adalah mereka bentuk dengan menggunakan perisian CST Microwave Design dan langkah lain adalah antena yang direka fabrikasi di papan FR4 dan d iukur. Kemudian, ukuran simulasi dan ukuran cetakan diukur, dianalisa dan dibandingkan.

ABSTRACT

This project is focused on dual polarized antenna design that operates at frequency of 2.4 GHz for mobile communication system. This antenna is able to generate two types if polarizations which are horizontal polarization and vertical polarization by using two ports. The motivation for this antenna design is due to reduce the interference that occurred during transmitting and receiving the signal to and from the antenna. The interference of the signal transmission often happens due to the weather and become critical during the bad weather. Therefore, this will causes low speed of transmission signal and does not satisfy the users demand nowadays. To satisfy this condition, the wider bandwidth antenna is needed. The dual polarization antenna is design in order to reduce the interference during transmitting or receiving signal as two type of polarization is being used which are vertical polarization and horizontal polarization. Polarization diversity is one of the handy techniques to improve performance between the transmitter and receiver microwave antennas because it can reduce spatial correlation that can decrease system performance. The design process can be divided into two design steps. First, the dual polarization antenna is designing by using the CST Design Microwave software and another step is the designed antenna being fabricated on FR4 board and measured. Then, the measurements in simulation and hardware antenna is being measured, analyzed and compared.

DEDICATION

A special feeling of gratitude to my loving parents, Azizan Bin Abdullah and Norma Binti Hat for their endless love, support and encouragement. A special thanks to my supervisor, En. Abdul Halim Bin Dahalan and my co-supervisor, En.

ACKNOWLEDGEMENT

Foremost, I would to thanks sincerely to my supervisor, En. Abdul Halim Bin Dahalan and my co-supervisor, En. Mohamad Zoinol Abidin bin Abd. Aziz for their advices and continuous support on my final year project. They had guided me and helped me a lot in order to achieve the purpose of doing the analysis on this work. They are both such a great leaders and become the mentors for my final year project.

I also would like to thank my fellow friends and lecturers who teach me with passion. Last but not least, I would like to thank my family member’s especially my mother, Norma Binti Hat for her special support and advise me a lot during the hard time I had faced before. She teaches me a lot and her spiritual support really means a lot to me.

TABLE OF CONTENT

Abstrak i

Abstract ii

Dedication iii

Acknowledgement iv

Table of Content v-vi

List of Tables vii

List of Figures viii- ix

List Abbreviations, Symbols and Nomenclatures x

CHAPTER 1: INTRODUCTION 1

1.1 Background 1-2

1.2 Problem statement 3

1.3 Objective 3

1.4 Scope 3

1.5 Project significant 4

1.6 Conclusion/Summary 4

CHAPTER 2: LITERATURE REVIEW 5

2.1 Mobile communication 5-6

2.2 Polarization 7-8

2.3 Antenna design 9

CHAPTER 3: METHADOLOGY 17

3.1 Literature review 17

3.2 Data collection 18

3.3 Design 19

3.4 Simulation 20

3.5 Simulation testing 21

3.6 Fabrication 22

3.7 Fabrication testing 23 3.8 Report writing 24-25

CHAPTER 4: RESULT & DISCUSSION 26

4.1 Antenna design specification 26-27

4.2 Parameter study of dual polarized antenna 28-29

4.3 Dimension of dual polarized antenna antenna. 30-33

4.4 Current distribution in two ports. 34-35

4.5 Return loss in Port 1 and Port 2. 4.5.1 Return loss in Port 1 4.5.2 Return loss in Port 2

36 36-37 38-40

4.6 Radiation pattern in Port 1 and Port 2. 41-42

4.7 3-D result and efficiency 43-45

4.8 Summary 46

CHAPTER 5: CONCLUSION & FUTURE WORK 47

5.1 Conclusion 47

5.2 Further research and development 48

5.3 Recommendation 49

REFERENCES 50-51

LIST OF TABLES

2.1 The cross-polar of the antenna design 10 2.2 The measured cross-polar, front-to-back ratio and gain. 11

4.1 Design specifications 26

4.2 Measurement for Antenna Configuration 30 4.3 The tabulate result for Port 1 and Port 2 39

LIST OF FIGURES

2.1 The diagram of difference type of mobile communication 5 2.2 Rotation of a plane electromagnetic wave and its polarization

ellipse at z = 0 as a function of time.

6

2.3 Geometry of proposed antenna element 8

2.4 Photo of the fabricated antenna element 9

2.5 Measured return loss and isolation 9

2.6 Simulated return loss with various R2 9

2.7 Effect of the U-shaped ground on the front-to-back ratio 10 2.8 Simulated VSWR with and without U-shaped ground 11 2.9 Measured E-plane radiation pattern for ±45º polarization. 13 2.10 Measured H-plane radiation pattern for §45± polarization. 14

3.1 Example of the design antenna. 19

3.2 Example of the antenna design simulation on CST software. 20 3.3 Example of the antenna design that has been fabricated. 22 3.4 The overall project methodology flowchart. 25

4.1 A compact dual polarized antenna designed 27 4.2 Parameter sweep for resonant frequency 2.4GHz for Ls 48-55 28 4.3 Parameter sweep for resonant frequency 2.4GHz for L230-37 28 4.4 Parameter sweep for resonant frequency 2.4GHz for W0(6,8,10) 29

4.5 Parameter sweep for resonant frequency 2.4GHz for Ws50-60 29 4.6 Antenna Configuration for Port 1 (Front view). 31 4.6 Antenna Configuration for Port 2 (Back view). 32 4.8 Antenna prototype (a) upper layer (b)bottom layer. 33 4.9 Electric field distribution in slot: feeding in (a) Port 1 and (b) 34

Port 2

4.11 Return Loss Graph for Port 1 36

4.12 Return Loss Graph for Port 2 38

4.13 Radiation pattern in Port 1 41

4.14 Radiation pattern in Port 2 42

4.15 Radiation pattern in 3D for Port 1 43

4.16 Radiation pattern in 3D for Port 2 43

6.1 The front and back antenna surface design in CST software. 52

6.2 Antenna in UV Exposure Machine 53

6.3 Antenna is placed in the etching machine. 53 6.4 Network analyzer is used to measure return loss 54 6.5 Calibration setup and antenna measurement. 55 6.6 The overall project methodology flowchart. 55

LIST OF ABBREVIATIONS, SYMBOLS AND

NOMENCLATURE

VSWR - Voltage Standing Wave Ratio

3D - 3 Dimension

e-plane - electric field plane h-plane - - magnetizing field plane

1

CHAPTER 1

INTRODUCTION

This section basically covered the introduction to the project work. It consists of background, problem statement, objective, scope, project significant and also the overall summary in this chapter.

1.1 Background

A specialized transducer that converts radio-frequency (RF) fields into alternating current (AC) is called antenna. There are two basic types of antenna. The first one is the receiving antenna where the intercepts RF energy and delivers AC to electronic equipment. The second type of antenna is the transmitting antenna which is fed with AC from electronic equipment and generates an RF field.

The polarization of an antenna definition is the polarization of the radiated fields produced by an antenna. It is evaluated in the far field. Hence, antennas can be classified as "Linearly Polarized" or a "Right Hand Circularly Polarized Antenna". To understand the concept of polarized antenna is the first, a horizontally polarized antenna will not communicate with a vertically polarized antenna. The antennas transmit and receive in exactly the same manner due to the reciprocity theorem. Therefore, transmitting and receiving vertically polarized fields occurs due to a vertically polarized antenna. Consequently, there will be no reception if a horizontally polarized antenna is trying to communicate with a vertically polarized antenna.

2 Dual polarized antenna is the antenna that can operate in horizontal polarization and also vertical polarization. The device can transmit data on one polarization and receive data on the other simultaneously by using dual polarized antenna.

Nowadays, our mobile telecommunication technology has grown up tremendously. The global cellular handset market is the most highly scalable technology market. Today, mobile communication applications such as the handset manufacturers are seeking an effective antenna solution suitable for implementing the next generation of cellular handset technologies. Currently, they are unable to achieve physically the desired antenna performance in a size that fits a cellular handset package at an acceptable volume cost.

Dual polarized antennas are design to improve communication capacity and quality by using the techniques of polarized diversity. By using this technique, these antennas are capable to eliminate the soldering process and limiting interfering with radiation from the radiation patches to the feed network. However, the problems are the slot radiates both in the patch direction and in the back direction which causes low gain and low front-to-back-ratio.

Therefore, this project discusses the design issues for dual polarized antenna for mobile communication applications for example in DCS, PCS and 3G mobile communication systems. The project will be conducted in software by using CST software and also the hardware by fabricate the circuit. The resulting performance of the parameters is compared and discussed.

3

1.2 Problem Statement

In order to improve the mobile communication applications system, we are craving for the great antennas but the antennas nowadays have weakness of resulting in low gain and low front-to-back ratio. This problems happened because of the slot radiates both in the patch direction. Therefore, to improve the antennas performances, the project is conducted to show the improvement in isolation between the polarization ports while maintaining a broad impedance bandwidth at 1.71-2.17 GHz.

1.3 Objective

The main objective of this project is to:

 Able to design, simulate and fabricate of dual polarized antenna in mobile communication application.

1.4 Scope

In this project, it would only covering existing mobile communication systems that operating at the frequency range 1.71-2.5 GHz. Furthermore, the parameter that will be measured are the return loss and isolation, and be able to simulate the radiation patterns at various angle. It is impossible to carry out the project to make a research on that investigate everything about the project topic.

4

1.5 Project Significant

From this project, the mobile communication application capacity and quality can be improved. In addition, this project will have a great contribution to the mobile manufacturers industry. This is because the project will improve the low gain and low front to-back ratio problems in dual polarized antennas. This will results in better mobile communication application such as in DCS, PCS, 3G and WLAN mobile communication system.

1.6 Conclusion/Summary

As a conclusion, this project is very important in order to improve our mobile communication applications system. This project will definitely contribute to our mobile manufacturers industry and the society with better communication system.

5

CHAPTER 2

LITERATURE REVIEW

A literature review is an evaluative report of studies that aims to find the literature that are related to this project. It also provides current knowledge as well as describes, summarize, evaluate and clarify this literature. It should be included a theoretical basis for the project. Besides that, literature review also used to generate knowledge and gather information used in this project by provide a context for the research, justify the research and outline gaps in previous research. In addition, literature review also helps to refine, refocus or even change the topic.

2.1 Mobile Communication

6 The growing demand for mobile communication nowadays makes the inventions of many technologies. Mobile technology is the technology used for cellular communication. Mobile code division multiple access (CDMA) technology has evolved rapidly over the past few years. Since the start of this millennium, a standard mobile device has being invented such as a mobile phone, GPS navigation device, an embedded web browser and instant messaging client, and a handheld game console. Therefore, many experts argue that the future of computer technology rests in mobile computing with wireless networking. In every wireless device required antenna to transfer the signal.

7

2.2 Polarization

According to Constantine A. Balanis in the Theory of Antenna states that polarization of an antenna in a given direction is defined as “the polarization of the wave transmitted (radiated) by the antenna. [2]

When the direction is not stated, the polarization is taken to be the polarization in the direction of maximum gain. In practice, polarization of the radiated energy varies with the direction from the center of the antenna. Therefore, different parts of the pattern may have different polarizations.

a) Rotation of wave b) Polarization ellipse

Figure 2.2: Rotation of a plane electromagnetic wave and its polarization ellipse at z = 0 as a function of time. [2]

One way to address the capacity increase is by employing polarization diversity. [3], [4] Recent results in communication theory [5] have demonstrated that deploying dual-polarized antennas at the transmitter and/or receiver can dramatically increase both the capacity and diversity of wireless communication links. For example, in the richly scattering environments considered in [5], a dual-polarized

8 antenna at the transmitter can increase capacity by more than 50% over a single transmit antenna; employing dual-polarized transmit and receive antennas can increase capacity threefold over a comparable system with single antennas at the transmitter and receiver.

According to C. Liu, J.L. Guo, Y.H. Huang, and L.Y. Zho (2012), the new design of a dual-polarized antenna with high isolation and low cross polarization is comprised two pairs of petaloid patches, which are fed by coaxial lines. Behind the patches, a U-shaped ground is placed to improve the front-to-back ratio of the antenna. Stable and symmetric radiation patterns at slanted ±45º polarization have been obtained within the frequency band 1.71-2.17 GHz. A return loss of |14| dB is achieved and measured isolation between the two input ports is over 31 dB. The 3 dB beamwidths of the two polarizations is stable (65±) and the average gain of the proposed antenna is about 9 dBi across the whole frequency band.[6]

In order to improve communications capacity and quality, many techniques are developed and applied. One of the most commonly used techniques is polarization diversity which is the antenna of the system should have dual polarization. The advantages are eliminating the soldering process and limiting interfering with radiation from the radiation patches to the feed network. But the slot radiates both in the patch direction and in the back direction, which results in low gain and low front-to-back ratio.

The antenna produces a low cross-polar level. Measured results show improvement in isolation between the polarization ports while maintaining a broad impedance bandwidth covering existing DCS, PCS and 3G mobile communication systems operating at 1.71-2.17 GHz. The 3 dB beamwidths of the two polarizations vary only several degrees over the frequency band. By contrast with aperture coupled antennas, this proposed antenna has the advantages of simple structure and low cost.

9

2.3 Antenna Design

(a) (b)

Figure 2.3: Geometry of proposed antenna element.

The basic configuration of the proposed antenna is illustrated in Figure 2.3. Two pairs of petaloid patches are printed on the FR4 substrate with a thickness of 0.8 mm. In an attempt to restrain the cross polarization generated by the petaloid patches, the squared metal fence with a side length of L1 is introduced and printed on the same substrate with the radiation patches. Four parts are dug inside the square patch in order to contain the petaloid patches.

Thus, all patches are printed on a single layer. The positions of feeds are symmetrical at the patches shown in Figure 2.3. There is a small gap with a length of 0.7mm between the adjacent patches. The U- shaped ground is utilized to generate the required front-to-back ratio for cell sector design. The radiation patches are separated from the ground with a height of 38mm which is ¸=4 at the center frequency 1.94 GHz.

Figure 2.4 presents the photo of the fabricated antenna. The whole structure was modeled using commercial software Ansoft HFSS with the following parameter details, L1 = 62 mm, L2 = 13:9 mm, L3 = 3:6 mm, L4 = 6 mm, w = 1 mm, R1 = 12:6 mm, R2 = 14 mm, H1 = 1:3 mm, H2 = 1:8 mm.

4 1.5 Project Significant

From this project, the mobile communication application capacity and quality can be improved. In addition, this project will have a great contribution to the mobile manufacturers industry. This is because the project will improve the low gain and low front to-back ratio problems in dual polarized antennas. This will results in better mobile communication application such as in DCS, PCS, 3G and WLAN mobile communication system.

1.6 Conclusion/Summary

As a conclusion, this project is very important in order to improve our mobile communication applications system. This project will definitely contribute to our mobile manufacturers industry and the society with better communication system.

5

CHAPTER 2

LITERATURE REVIEW

A literature review is an evaluative report of studies that aims to find the literature that are related to this project. It also provides current knowledge as well as describes, summarize, evaluate and clarify this literature. It should be included a theoretical basis for the project. Besides that, literature review also used to generate knowledge and gather information used in this project by provide a context for the research, justify the research and outline gaps in previous research. In addition, literature review also helps to refine, refocus or even change the topic.

2.1 Mobile Communication

6 The growing demand for mobile communication nowadays makes the inventions of many technologies. Mobile technology is the technology used for cellular communication. Mobile code division multiple access (CDMA) technology has evolved rapidly over the past few years. Since the start of this millennium, a standard mobile device has being invented such as a mobile phone, GPS navigation device, an embedded web browser and instant messaging client, and a handheld game console. Therefore, many experts argue that the future of computer technology rests in mobile computing with wireless networking. In every wireless device required antenna to transfer the signal.

7 2.2 Polarization

According to Constantine A. Balanis in the Theory of Antenna states that polarization of an antenna in a given direction is defined as “the polarization of the wave transmitted (radiated) by the antenna. [2]

When the direction is not stated, the polarization is taken to be the polarization in the direction of maximum gain. In practice, polarization of the radiated energy varies with the direction from the center of the antenna. Therefore, different parts of the pattern may have different polarizations.

a) Rotation of wave b) Polarization ellipse

Figure 2.2: Rotation of a plane electromagnetic wave and its polarization ellipse at z

= 0 as a function of time. [2]

One way to address the capacity increase is by employing polarization diversity. [3], [4] Recent results in communication theory [5] have demonstrated that deploying dual-polarized antennas at the transmitter and/or receiver can dramatically increase both the capacity and diversity of wireless communication links. For example, in the richly scattering environments considered in [5], a dual-polarized

8 antenna at the transmitter can increase capacity by more than 50% over a single transmit antenna; employing dual-polarized transmit and receive antennas can increase capacity threefold over a comparable system with single antennas at the transmitter and receiver.

According to C. Liu, J.L. Guo, Y.H. Huang, and L.Y. Zho (2012), the new design of a dual-polarized antenna with high isolation and low cross polarization is comprised two pairs of petaloid patches, which are fed by coaxial lines. Behind the patches, a U-shaped ground is placed to improve the front-to-back ratio of the antenna. Stable and symmetric radiation patterns at slanted ±45º polarization have been obtained within the frequency band 1.71-2.17 GHz. A return loss of |14| dB is achieved and measured isolation between the two input ports is over 31 dB. The 3 dB beamwidths of the two polarizations is stable (65±) and the average gain of the proposed antenna is about 9 dBi across the whole frequency band.[6]

In order to improve communications capacity and quality, many techniques are developed and applied. One of the most commonly used techniques is polarization diversity which is the antenna of the system should have dual polarization. The advantages are eliminating the soldering process and limiting interfering with radiation from the radiation patches to the feed network. But the slot radiates both in the patch direction and in the back direction, which results in low gain and low front-to-back ratio.

The antenna produces a low cross-polar level. Measured results show improvement in isolation between the polarization ports while maintaining a broad impedance bandwidth covering existing DCS, PCS and 3G mobile communication systems operating at 1.71-2.17 GHz. The 3 dB beamwidths of the two polarizations vary only several degrees over the frequency band. By contrast with aperture coupled antennas, this proposed antenna has the advantages of simple structure and low cost.

9 2.3 Antenna Design

(a) (b)

Figure 2.3: Geometry of proposed antenna element.

The basic configuration of the proposed antenna is illustrated in Figure 2.3. Two pairs of petaloid patches are printed on the FR4 substrate with a thickness of 0.8 mm. In an attempt to restrain the cross polarization generated by the petaloid patches, the squared metal fence with a side length of L1 is introduced and printed on the same substrate with the radiation patches. Four parts are dug inside the square patch in order to contain the petaloid patches.

Thus, all patches are printed on a single layer. The positions of feeds are symmetrical at the patches shown in Figure 2.3. There is a small gap with a length of 0.7mm between the adjacent patches. The U- shaped ground is utilized to generate the required front-to-back ratio for cell sector design. The radiation patches are separated from the ground with a height of 38mm which is ¸=4 at the center frequency 1.94 GHz.

Figure 2.4 presents the photo of the fabricated antenna. The whole structure was modeled using commercial software Ansoft HFSS with the following parameter details, L1 = 62 mm, L2 = 13:9 mm, L3 = 3:6 mm, L4 = 6 mm, w = 1 mm, R1 = 12:6 mm, R2 = 14 mm, H1 = 1:3 mm, H2 = 1:8 mm.