a multi-band microstrip antenna for mobile...

A MULTI-BAND MICROSTRIP ANTENNA FOR MOBILE HANDSET

TAN ZEE YEAN

UNIVERSITI TEKNOLOGI MALAYSIA

PSZ 19:16 (Pind. 1/97) UNIVERSITI TEKNOLOGI MALAYSIA

BORANG PENGESAHAN STATUS TESIS♦ JUDUL: A MULTI-BAND MICROSTRIP ANTENNA FOR MOBILE HANDSET

SESI PENGAJIAN: 2007/2008

Saya TAN ZEE YEAN

(HURUF BESAR)

mengaku membenarkan tesis (PSM/Sarjana/Doktor Falsafah)* ini disimpan di Perpustakaan Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut:

1. Tesis adalah hakmilik Universiti Teknologi Malaysia. 2. Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan pengajian sahaja. 3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara institusi pengajian tinggi. 4. **Sila tandakan ( 4 )

Disahkan oleh

(TANDATANGAN PENULIS) (TANDATANGAN PENYELIA) Alamat Tetap: 58, KAMPUNG BARU, SEMELING, DR. NORHISHAM BIN HJ KHAMIS 08100 BEDONG, KEDAH. Nama Penyelia Tarikh: MAY 2008 Tarikh: MAY 2008

CATATAN: * Potong yang tidak berkenaan.

** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan

tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD. ♦ Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah dan Sarjana secara

penyelidikan, atau disertasi bagi pengajian secara kerja kursus dan penyelidikan, atau Laporan Projek Sarjana Muda (PSM).

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

TERHAD (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan)

TIDAK TERHAD

√

TianSiak

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TianSiak

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“I hereby declare that I have read this thesis and in

my opinion this thesis is sufficient in terms of scope and

quality for the award of the degree of Electrical-Telecommunication Engineering”

Signature : ………………………………………...

Name of Supervisor : Dr. NOR HISHAM BIN HJ KHAMIS

Date : MAY 2008

TianSiak

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A MULTI-BAND MICROSTRIP ANTENNA FOR MOBILE HANDSET

TAN ZEE YEAN

This thesis is submitted in fulfillment for the Requirement for the award of the degree of

Electrical Engineering (Telecommunication)

Faculty of Electrical Engineering Universiti Teknologi Malaysia

MAY 2008

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“I declare that this thesis entitled “A Multi-Band Microstrip Antenna for mobile

Handset” is the result of my own research except as cited in the references. The

thesis has not been accepted for any degree and is not concurrently submitted in

candidature of any degree”.

Signature : ………………………….

Name : TAN ZEE YEAN

Date : MAY 2008

TianSiak

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To my beloved family and friends for their unconditional love and support

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ACKNOWLEDGEMENT

First and foremost, I would like to grab this opportunity to express my sincere

gratitude to my project supervisor, Dr. Nor Hisham bin Haji Khamis for the

guidance, motivation, inspiration, encouragement and advice throughout the duration

of completing this project. Without his never ending support and interest, this thesis

would not have been the same as presented here.

My sincere appreciation also extends to all my housemates who have

provided assistance at various occasions.

Not forgetting my fellow course mates and friends, who shared a lot of

technical knowledge with me, encourage me to seek for more knowledge and

providing me some troubleshooting tips.

I would like to thank the staffs of Microwave Laboratory for providing assistance.

To my beloved family who has always been there to encourage, comfort and

give their fullest support when I most needed them.

Last but not least, I would like to express my gratitude to all who have

directly or indirectly helped me in completing my project.

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ABSTRACT

Wireless communications have progressed rapidly in recent years, and many

mobile units are becoming smaller in size. To meet the miniaturization requirement,

the antennas employed in mobile terminals must have also their dimensions reduced

accordingly. Planar antennas, such as microstrip and printed antennas have the

attractive features of low profile, small size, and conformability to mounting hosts

and are very promising candidates for satisfying this design consideration. For this

reason, compact and broadband design technique for planar antennas have attracted

much attention from antenna researches. Very recently, especially after the year

2000, many novel planar antenna designs to satisfy specific bandwidth specifications

of present-day mobile cellular communications systems, this project reviews the

designs and get a compact structure capable of broadband operation including the

Global System for Mobile Communication (GSM; 890-960 MHz) band, centered at

900 MHz; the Digital Communication System (DCS; 1710-1880 MHz) band,

centered at 1800 MHz; and the Personal Communication System (PCS; 1850-1990

MHz) band, centered at 1900 MHz and the Universal Mobile Telecommunication

system (UMTS; 1920-2170 MHz) band, centered at 2 GHz.

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ABSTRAK

Bidang perhubugan wayerless telah berkembang secara pesatnya dalam

beberapa tahun ini, dan telah mengakibatkan pengecilan saiz telefon mudah alih.

Untuk mencapai pengurangan dari segi saiz, antenna telefon mudah alih perlu

dikecilkan mengikut diamensi. Antena satah seperti mikrostrip dan antena printed

,mempunyai ciri-ciri yang menarik seperti profil rendah, ringan, teknik pembuatan

yang mudah, dan mempunyai keseragaman dalam proses pemasangan dan ia

merupakan calon yang paling berpotensi untuk memenuhi keperluan rekabentuk.

Oleh sebab ini, teknik rekabentuk mengurangkan saiz antenna dan beroperasi pada

jalur lebar untuk antena satah sangat diminati oleh ramai penyelidik. Baru-baru ini,

terutamanya selepas tahun 2000, banyak antena yang baru direkabentuk untuk

memenuhi jalur lebar yang tertentu dan beroperasi pada jalur frekuensi yang berbeze.

Project ini merujuk rekabentuk tersebut dan seterusnya mendapatkan satu sruktur

yang padat yang berupaya beroperasi pada jalur lebar dalam frekuensi yang berbeza

yang digunapakai pada empat piawai – GSM900 (Sistem Bergerak Global), GPS

(Sistem Kedudukan Global), DCS1800 (Sistem Selular Digital), PCS (Sistem

Telekomunikasi Peribadi) dan UMTS2000 ( Sistem Telekomunikasi Bergerak

Universal).

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF ABBREVIATIONS xiii

LIST OF APPENDENCES xiv

1 INTRODUCTION 1

1.1 Overview 1

1.2 Problem Statement 3

1.3 Objective 4

1.4 Scope of Work 4

1.5 Methodology 5

1.6 Thesis Outline 6

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2 LITERATURE REVIEW 8

2.1 Introduction 8

2.1.1 From Analog to Digital Systems 8

2.2 Antenna for Mobile Phones 12

2.3 Microstrip Antenna 13

2.3.1 Advantages and Disadvantages of 14

Microstrip Antennas

2.3.2 Applications of Microstrip Antennas 15

3 THEORY OF MICROSTRIP PATCH ANTENNA 17

3.1 Basic Characteristics of Microstrip Patch Antenna 17

3.2 Analysis of Microstrip 18

3.3 Fundamentals of Transmission Line 21

3.3.1 Coaxial Cable 22

3.3.2 Microstrip Transmission Line 23

3.4 Substrate Materials 24

3.5 Microstrip Transmission Line Design Formulas 25

3.5.1 Effective Dielectric Constant 25

3.5.2 Wavelength 27

3.5.3 Characteristic Impedance 27

3.5.4 Synthesis Equations 28

3.6 Design of Rectangular Microstrip Antenna 29

4 ANTENNA DESIGN AND PROCEDURES 31

4.1 Introduction 31

4.2 Starting Point 33

4.3 The Proposed Antenna Design 39

4.3.1 The Design Specifications 39

4.3.2 Antenna Structure 40

4.4 The Simulation Software 45

4.5 The Fabrication Process 45

4.6 The Measurement Stage 46

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5 RESULTS AND DISCUSSION 47

5.1 Introduction 47

5.2 Return Loss 48

5.2.1 The Simulation Return Loss 48

5.2.2 The Measured Return Loss 53

5.2.2.1 Set One Antenna 54

5.2.2.2 Set Two Antenna 56

5.3 Radiation Pattern 59

5.4 Antenna Prototype 61

6 CONCLUSIONS 64

6.1 Conclusions 64

6.2 Recommendations for Future Work 65

REFERENCES 67

APPENDICES A-D 69-77

x

LIST OF TABLES

TABLE NO. TITLE PAGE

1.1 Frequency Bands for Wireless Applications 3

3.1 Comparisons of Transmission Lines 22

5.1 Comparison of Return Loss between the six proposed 51

antenna design

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 Antenna Design and Development Flow Chart 5

2.1 Microstrip Antenna Configurations 14

3.1 Physical Structure of a Microstrip Patch Antenna 18

3.2 Microstrip Patch Geometries 18

3.3 Microstrip Line (Quasi-TEM Mode) 19

3.4 Radiation Mechanism of Rectangular Microstrip Patch 21

3.5 Coaxial Cable 22

3.6 Structure of Microstrip Transmission Line 24

3.7 Wide and Narrow (Width) Microstrip Line 26

3.8 Rectangular Patch 29

4.1 Work Flow 31

4.2 Geometry and dimensions of the proposed low-profile planar 33

monopole antenna for GSM/DCS/PCS/UMTS operation

4.3 Measured and simulated return loss for the proposed antenna 35

4.4 Simulated IE3D results of the surface current distributions 35

on the radiating patch for the proposed antenna at 900, 1800,

1900, and 2050 MHz

4.5 Measured radiation patterns for the proposed antenna at 36

900 MHz and 1800 MHz

4.6 Measured radiation patterns for the proposed antenna at 37

1900 MHz and 2050 MHz

4.7 Measured antenna gain for the proposed antenna 38

4.8 Proposed Multi-band Microstrip Antenna (Design 1) 42

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4.14 Etching Machine 46

4.15 Marconi Test Equipment 46

5.1 The Simulated Return Loss for Designed Antenna (Design1) 48






5.7 The Measured Return Loss (Set One Design1) 54



5.10 The Measured Return Loss (Set Two Design1) 57



5.13 The Radiation Pattern for 1.8GHz Band (Design1) 59



5.16 The Fabricated Antenna Design1 (Set One) 61



5.19 The Fabricated Antenna Design1 (Set Two) 62



xiii

LIST OF ABBREVIATIONS

AMPS - Advanced Mobile Phone Service

CDMA - Code Division Multiple Access

DCS - Digital Communication System

GPS - Global Position System

GSM - Global System for Mobile Communication

EM - Electromagnetic

IFAs - inverted-F shaped wire-form antennas

IMT-2000 - International Mobile Communications-2000

MIC - Microwave Integrated Circuit

PCB - Printed Circuit Board

PCS - Personal Communication System

PIFAs - Planar Inverted-F Antennas

TACS - Total Access Communications System

TDMA - Time Division Multiple Access

TEM - Transverse-Electric-Magnetic

UMTS - Universal Mobile Telecommunication System

VSWR - Voltage Standing Wave Ratio

WLAN - Wireless Local Area Network

1G - First Generation

2G - Second Generation

2.5G - Evolved Second Generation

3G - Third Generation

4G - Fourth Generation

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LIST OF APPENDICES

APPENDIX. TITLE PAGE

A Designed Procedures Using Microwave Office 69

B Return Loss Measurement 73

C1 Equipment used for Antenna Testing 75

C2 Equipment used for PCB Fabrication 76

D Components and Price List 77

Chapter 1

Introduction

1.1 Overview

Wireless and mobile communications is one of the fastest growing areas of

modern life. It has an enormous impact on almost every aspect of our daily lives.

Moreover, it have progressed very rapidly in recent years, and many mobile units are

becoming smaller and smaller. There are also some demands for the mobile phones

to be attractive, lightweight and curvy. In order to meet the miniaturization

requirement, the antennas employed in mobile terminals must have their dimensions

reduced accordingly. Besides, this has resulted production of handsets with antennas

that are internal or hidden within the device. An internal antenna makes the handset

look much nicer and compact compared to the conventional monopole-like antennas

which remained relatively large antenna height. Therefore, build in antennas

becoming very promising candidates for applications in mobile phones.

Currently, most built-in antennas used in mobile phones include microstrip

antennas, inverted-F shaped wire-form antennas (IFAs), and planar inverted-F

antennas (PIFAs). Planar antennas, such as microstrip and printed antennas have the

attractive features of low profile, light weight, compact size and volume, and

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conformability to mounting hosts [1] and low fabrication costs are very talented

candidates for satisfying the design consideration. Besides, PIFAs also being used as

internal antenna as it has more advantages on microstrip antenna. Conceptually, it

can be designed to have a wide-bandwidth, so it can operates in dual-band and tri-

band phones. PIFA renders itself capable of operating in two or more discrete

frequency bands, multiband. In addition, PIFAs is currently used as it’s concealable

within the housing of the mobile phones. It also capable reduces backward radiation

toward the user’s head and enhances antenna performance.

For these reasons, compact and broadband design techniques for planar

antennas [2] have attracted much attention from antenna researches. Recently,

especially after the year 2000, many novel planar antenna designs to satisfy specific

bandwidth specifications of present-day mobile cellular communications system

have been developed. Designing an internal antenna for a mobile phone is difficult

especially when dual or multi-band operation is required. Although obtaining dual-

frequency resonance is straightforward, satisfying the bandwidth requirement for the

respective communication bands is difficult. Further complications arise when the

antenna has to operate in close proximity to objects like shielding cans, screws,

battery, and various other metallic objects. At present, many mobile telephones use

one or more of the following frequency bands: the Global System for Mobile

Communication (GSM; 890-960 MHz) band, centered at 900 MHz; the Digital

Communication System (DCS; 1710-1880 MHz) band, centered at 1800 MHz; and

the Personal Communication System (PCS; 1850-1990 MHz) band, centered at 1900

MHz and the Universal Mobile Telecommunication system (UMTS; 1920-2170

MHz) band, centered at 2 GHz.

3

Table 1.1: Frequency bands for wireless applications

Wireless Applications Frequency Bands (MHz)

Global System for Mobile Communication

GSM-900

890-960

Digital Communication System DCS-1800 1710-1880

Personal Communication System PCS-1900 1850-1990

Universal Mobile Telecommunication system

UMTS-2000

1920-2170

Bluetooth and Wireless Local Area Network

WLAN

2400-2484

1.2 Problem Statement

Different wireless standards are available for mobile communication, thus, it

required a same device that can operate in different frequency bands. Therefore,

multi-band antennas which provide the feature of multi-band reception is needed

since it is not possible to equip the device with many antenna for each frequency.

Besides, the sizes and weights of mobile phones have been rapidly reduced

due to the development of integrated circuit technology and requirements of users.

Moreover, in recent years, the demand for compact handheld communication devices

has grown significantly.

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1.3 Objective

The main objective of this project is to design and develop a multi-band

and/or wide-bandwidth antenna which could operate at different wireless frequency

bands such as GSM-900, DCS-1800, PCS-1900 and 3G-2000.

1.4 Scope of Work

The main emphasis of the project is to design and develop a multi-band

microstrip antenna. In order to achieve that, the project is divided into software and

hardware parts. At start, a comprehensive literature review is required to obtain

knowledge on antenna design. Furthermore, several types of antennas with optimal

working frequency and PCB specifications is proposed and developed.

The designed antenna is then being verified and improves using simulation

software such as Microwave Office. The antenna design parameters are optimizes to

satisfy the best return loss and radiation pattern in frequency bands. Then, a

prototype antenna will be fabricated and comparisons will be made between

simulation and measurement results.

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1.5 Methodology of Project

Figure 1.1 Antenna design and development flow chart

In order to achieve the objectives of the project, at the first phase of work, a

comprehensive literature review on multi-band microstrip antenna is required. This is

to get an antenna that requires minimal modification to suit the specifications of the

project.

Then, the process is continues with design or develop the antenna design.

Besides, in design and simulation stage, antenna design is simulate using simulation

software Microwave Office. In the second stage of work which reached the prototype

stage, antenna is being fabricated. The prototype is being fabricated, conduct

experiments and compare the performance of the antenna between simulated and

measured results.

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1.6 Thesis Outline

In generally, this thesis is divided into six chapters. Each chapter will discuss

on different issues related to the project. Following are the outline for each chapter:

Chapter one discusses on the introduction and overview of the project

background, problem statement, objective, scope of the work and methodology to

carry out the work.

Meanwhile, Chapter two focuses on the literature review used to assist the

project. It presents some general review on mobile generation and its characteristics

and the stages of developing it from analog to digital systems, and some general

antennas on mobile phones. Besides, this chapter also introduces theory behind

microstrip antenna, advantages and disadvantages of microstrip antennas and also

the applications of microstrip antennas.

Chapter three shows the theory of microstrip patch antenna. It consists basic

characteristics of microstrip patch antenna and the analysis of microstrip.

Furthermore, it deals with the fundamentals of transmission line such as coaxial

cable and microstrip transmission line. Besides, substrate materials, microstrip

transmission line design formulas, effective dielectric constant, wavelength,

characteristic impedance, the synthesis equations, and basic formula to design a

rectangular microstrip antenna are the topics discussed in this chapter.

Chapter four explains on the antenna design and its procedures. An IEEE

article which is set as the main reference of this project is included. In addition, the

proposed antenna designs, the antenna structure and specifications are being

presented. The simulation software Microwave Office, the fabrication process and

also the measurement stage is being introduced.

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Chapter five introduces the simulation and measured return loss and has a

discussion for these results. Comparison are made between the simulation and

measured result. Besides, simulation result for radiation pattern and antenna

prototypes are attached.

Chapter six is devoted to conclusion and recommendations for future work

that can be done for more enhancements for the antenna.

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

At the start of the 21st century, the wireless mobile markets are witnessing

unprecedented growth fueled by an information explosion and a technology

revolution. In the radio frequency arena, the trend is to move from narrowband to

wideband with a family of standards tailored to a variety of application needs.

Besides, there are a variety of wireless communication systems for transmitting

voice, video, and data in local or wide areas. There are point-to-point wireless

bridges, wireless local area networks, multidirectional wireless cellular systems, and

satellite communication systems.

2.1.1 From Analog to Digital Systems

Mobile wireless analog communication systems have been around since the

1950s. The early systems were single channel "over-and-out" systems. Instead of a

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cellular configuration, a single radio tower serviced a metropolitan area, which

severely limited the scalability of the systems. Service quality varied depending on

the location of the caller. Later systems added multiple two-way channels but still

had limited capacity.

Analog cellular services were introduced by AT&T in the 1970s and became

widespread in the 1980s. The primary analog service in the United States is called

AMPS (Advanced Mobile Phone Service). There are similar systems around the

world that go by different names. The equivalent system in England is called TACS

(Total Access Communications System).

The AMPS system is a circuit-oriented communication system that operates

in the 824-MHz to 894-MHz frequency range. This range is divided into a pool of

832 full-duplex channel pairs (1 send, 1 receive). Any one of these channels may be

assigned to a user. A channel is like physical circuit, except that it occupies a specific

radio frequency range and has a bandwidth of 30 kHz. The circuit remains dedicated

to a subscriber call until it is disconnected, even if voice or data is not being

transmitted.

Cellular systems are described in multiple generations, with third- and fourth-

generation (3G and 4G) systems just emerging:

• First generation (1G system) These are the analog systems such as

AMPS that grew rapidly in the 1980s and are still available today.

Many metropolitan areas have a mix of 1G and 2G systems, as well as

emerging 3G systems. The systems use frequency division

multiplexing to divide the bandwidth into specific frequencies that are

assigned to individual calls.

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• Second generation (2G systems) These second-generation systems

are digital, and use either TDMA (Time Division Multiple Access) or

CDMA (Code Division Multiple Access) access methods. The

European GSM (Global System for Mobile communications) is a 2G

digital system with its own TDMA access methods. The 2G digital

services began appearing in the late 1980s, providing expanded

capacity and unique services such as caller ID, call forwarding, and

short messaging. A critical feature was seamless roaming, which lets

subscribers move across provider boundaries.

• Evolved second generation (2.5G) Improved data services (packet

data and higher bit rates) GPRS (packet data in GSM) and EDGE

(higher bit rates within GSM).

• Third generation (3G systems) 3G has become an umbrella term

to describe cellular data communications with a target data rate of 2

Mbits/sec. The ITU originally attempted to define 3G in its IMT-2000

(International Mobile Communications-2000) specification, which

specified global wireless frequency ranges, data rates, and availability

dates. However, a global standard was difficult to implement due to

different frequency allocations around the world and conflicting input.

So, three operating modes were specified.

• Fourth generation (4G Systems) On the horizon are 4G systems

that may become available even before 3G matures (3G is a confusing

mix of standards). While 3G is important in boosting the number of

wireless calls, 4G will offer true high-speed data services.

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The move to digital technologies opened up the wireless world. It improved

capacity, reduced equipment costs, and allowed for the addition of new features.

Reduced handset costs meant more people were vying for services and taxing

systems. 3G systems add more capacity. In addition, packet technologies were

developed that use bandwidth more efficiently. The primary 1G and 2G digital

systems are listed here.

• Analog cellular These are the traditional analog systems such as

AMPS and TACS that use frequency division multiplexing. AMPS

operate in the 800-MHz range, while TACS operates in the 900-MHz

frequency range.

• Hybrid analog/digital cellular (usually called digital

cellular) These systems are analog AMPS systems in which

digitized voice and digital data is modulated onto the analog sine

wave of the channel being used. They operate in the same 800-MHz

range as analog AMPS and even use the same topology and

equipment configuration (cells, towers, etc.). The access method may

be either TDMA or CDMA, as discussed in the next section.

• GSM (Global System for Mobile Communications) This is a

second-generation mobile system designed from the ground up

without trying to be backward compatible with older analog systems.

GSM is popular in Europe and Asia, where it provides superior

roaming ability among countries. It uses TDMA, but Europe is

moving from this system into 3G systems based on a wideband form

of CDMA.

• UMTS (Universal Mobile Telecommunications System) Standing

for "Universal Mobile Telecommunications System", UMTS

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represents an evolution in terms of capacity, data speeds and new

service capabilities from second generation mobile networks. Today,

more than 60 3G/UMTS networks using WCDMA technology are

operating commercially in 25 countries, supported by a choice of over

100 terminal designs from Asian, European and United States (US)

manufacturers. Japanese operator NTT DoCoMo launched the world's

first commercial WCDMA network in 2001.

When digital cellular services were being designed in the early 1980s, the

choice was to design a system that was backward compatible with existing analog

systems (and used the same frequency allocation) or to design a whole new system.

The European community had about seven incompatible analog services, so it

created the GSM system from scratch to operate in the 900-MHz range (and later in

the 1,800-MHz range).

2.2 Antennas for Mobile Phones

An antenna is defined by Webster’s Dictionary as “a usually metallic device

(as a rod or wire) for radiating or receiving radio waves.” The IEEE Standard

Definitions of Terms of Antennas (IEEE Std 145-1983) [3] defines the antenna or

aerial as “a means for radiating or receiving radio waves.” In other words the antenna

is the transitional structure between free space and a guiding device.

In general, the antennas used in mobile phones are expected to have certain

characteristics:

1. Minimum occupied volume with regard to portability and overall size

minimization of the mobile terminal and shape.

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2. Light weight.

3. Conformability to mounting hosts.

4. Multi-band operation for different communication standards.

5. Adequate bandwidth covering the frequency range used by the system,

including a safety margin for production tolerances.

6. Isotropic radiation characteristics (omnidirectional).

7. Negligible human body effect.

8. Low fabrication costs since it is a mass produced consumer item.

2.3 Microstrip Antenna

The concept of microstrip radiators was first proposed by Deschamps [4] as

early as 1953. However, twenty years passed before practical antenna were

fabricated, as better theoretical models and photo-etch techniques for copper or gold-

clad dielectric substrates with a wide range of dielectric constants, attractive thermal

and mechanical properties and of low loss tangent were developed. The first practical

antennas were developed in the early 1970’s by Howell and Munson. Since then,

extensive research and development of microstrip antennas and arrays, exploiting the

numerous advantages such as light with integrated circuits, etc., have led to

diversified applications and to the establishment of the topic as a separate entity

within the broad field of microwave antennas.

As shown in Figure 2.1, a microstrip antenna in its simplest configuration

consists of a radiating patch on one side of a dielectric substrate ( 10≤rε ), which

has a ground plane on the other side. The patch conductors, normally of copper and

gold, can assume virtually any shape, but conventional shapes are generally used to

simplify analysis and performance prediction. Ideally, the dielectric constant, rε of

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the substrate should be low ( 5.2≈rε ), so as to enhance the fringe fields which

account for the radiation.

Figure 2.1 Microstrip Antenna Configurations

2.3.1 Advantages and Disadvantages of Microstrip Antennas

Microstrip antennas have several advantages compared to conventional

microwave antennas and therefore many applications over the broad frequency

from 100MHz to 50GHz. Some of the principal advantages of microstrip antennas

compared to conventional microwave antennas are:

• Lightweight, low volume, low profile, planar configurations which can

be made conformal

• Low fabrication cost; readily amenable to mass production

• Can be made thin; hence, they do not perturb the aerodynamics of host

aerospace vehicles

• The antennas may be easily mounted on missiles, rockets and satellites

without major alternations

• The antennas have low scattering cross section

15

• Linear, circular (left hand or right hand) polarizations are possible with

simple changes in feed position

• Dual frequency antennas easily made

• No cavity backing required

• Microstrip antennas are compatible with modular designs (solid state

devices such as oscillators, amplifiers, variable attenuators, switches,

modulators, mixers, phase shifters etc. can be added directly to the

antenna substrate board)

• Feed lines and matching networks are fabricated simultaneously with

the antenna structure

However, microstrip antennas also have some disadvantages compared to

conventional microwave antennas including:

• Narrow bandwidth

• Loss, hence somewhat lower gain

• Most microstrip antenna radiate into a half plane

• Practical limitations on the maximum gain ( ≈ 20dB)

• Poor endfire radiation performance

• Poor isolation between the feed and the radiating elements

• Possibility of excitation of surface waves

• Lower power handling capability

2.3.2 Applications of Microstrip Antennas

For many practical designs, the advantages of microstrip antennas far

outweigh their disadvantages. Even though the field of microstrip antennas now

may be considered to be still in its infancy, there are many different, successful

16

applications. With continuing research and development and increased usage of

microstrip antennas it is expected that they will ultimately replace conventional

antennas for most applications. Some notable system applications for which

microstrip antennas have been developed include [4]:

• Satellite communication

• Doppler and other radars

• Radio altimeter

• Command and control

• Missile telemetry

• Weapon fusing

• Man pack equipment

• Environmental instrumentation and remote sensing

• Feed elements in complex antennas

• Satellite navigation receiver

• Biomedical radiator

CHAPTER 3

THEORY OF MICROSTRIP PATCH ANTENNA

3.1 Basic Characteristics of Microstrip Patch Antenna

The basic microstrip patch antenna is made up of a thin sheet of low-loss

insulating material called the dielectric substrate (Figure 3.1). It is considered the

mechanical backbone of the microstrip circuit as it provides a stable support for the

conductor strips and patches that make up connecting lines, resonators and

antennas. Furthermore, it fulfills an electrical function by concentrating the

electromagnetic fields and preventing unwanted radiation in circuits.

The electrical characteristics of the antenna are also largely determined by

its permittivity and thickness. The bottom layer of the dielectric is completely

covered with metal and this is known as the ground plane. The topside of the

dielectric is partly metalized or patched whereby antenna or circuit pattern can be

printed. Figure 3.2 depicts the different shapes, which the radiating patch element

may take the form of. The attractive radiation characteristics, especially low cross

polarization radiation makes the square, rectangular, dipole (strip) and circular shapes the

simplest and common in terms of analysis and fabrication.

18

Figure 3.1 Physical Structure of a Microstrip Patch Antenna

Figure 3.2: Microstrip Patch Geometries

3.2 Analysis of Microstrip

The microstrip is essentially an inhomogeneous transmission line because the

fields are not contained completely in the substrate. As a result, this transmission line

cannot support pure transverse-electric-magnetic (TEM) mode of transmission, as

phase velocities would be different in the air and the substrate. Instead, the dominant

mode of propagation for the microstrip lines is the quasi-TEM mode as observed in

Figure 3.3.

19

Figure 3.3: Microstrip Line (Quasi-TEM Mode)

Physically, microstrip antennas radiate because electric currents flow on

the surface of metal patches and ground plane. Every elementary surface of both

conductors contributes to radiation, directly or indirectly, through the excitation

of the different waves described in the earlier section. Summing up the fields of

the waves contributed by all elementary surfaces thus yield the complete field

configuration. Therefore, the microstrip antenna has a maximum of its radiation

pattern broadside to the plane of the antenna as it radiates power in a beam

broadside to the plane of the antenna and displays an input impedance similar to a

parallel resonant circuit near its operating frequency.

Considering a basic microstrip in its simplest configuration with a

radiating metallic patch on one side of a dielectric substrate ( 10≤rε ) and a

ground plane on the under side, the idea of radiation from microstrip antennas can

be understood. The dielectric constant of the substrate should ideally be low

( 5.2≈rε ) to enhance fringing fields, which forms the basis of useful radiation in

this application. Most microstrip antennas possess radiating elements on one side

of a dielectric substrate and can be fed by any of the feed techniques introduced

later.

20

The concept of radiation from microstrip antennas can be understood by first

considering a simple case of a rectangular microstrip patch spaced a fraction of a

wavelength above a ground plane as shown in Figure 3.4. Radiation occurs from the

fringing fields between the edge of the microstrip conductor and the ground plane

when the microstrip structure is about half a wavelength (2λ ) long, assuming no

variations of the electric fields along the width and the thickness of it.

The fields at the end can be resolved into normal and tangential

components with respect to the ground plane. The normal components are out of

phase as the patch line is (2λ ) long. This means that the far fields produced by

them cancel in the broadside direction. The tangential components, which are in

phase means that the resulting fields combine to give maximum radiated field

normal to the surface of the structure (i.e. the broadside direction). Hence, the

patch can be represented as two slots 2λ apart excited in phase and radiating in

the half space above the ground plane (Figure 3.4b).

The variations of field along the width of the patch can also be considered

by the same analogy. The antenna can be represented by four slots that surround the

patch structure. Similarly, equivalent slots may also represent all the other microstrip

configurations. As such, radiation field can be determined since the fields in the slots

are known accurately and equivalent current sources can thus be calculated

accordingly.

21

Figure 3.4: Radiation Mechanism of Rectangular Microstrip Patch

3.3 Fundamentals of Transmission Line

The purpose of transmission line is to deliver all the signal power to the

antenna with the least possible power loss which depends on the special physical and

electrical characteristics (impedance and resistance) of the transmission line.

There are many type of transmission line suitable for microwave system

depends on their applications and availability of technology. Basically, there are

classified in three basic forms which are waveguide, coaxial cable and microstrip

line.

Each type has its own usage, their advantages and disadvantages briefly

shown in Table 3.1:

22

Table 3.1: Comparisons of Transmission Lines

Type Waveguide Coaxial cable Microstrip line

Advantages -Low attenuation

-High power

-Larger bandwidth

-Small size

-Easy to connect

multiple lines

together

Disadvantages -Limited bandwidth

-Large size

-High attenuation

-Low power

-Very high

attenuation

-Low power

3.3.1 Coaxial Cable

Coaxial cable is defined as two wires which shape in concentric and

cylindrical, separated by dielectric (insulator). Normally, there are two kinds of

insulator being used, which is air and helical insulator. The length of center

conductor is 2a while the length of outer conductor is 2b as shown in Figure 3.5.

These conductors are cover by protective jacket. The protective jacket is then

covered by an outer protective armor.

Figure 3.5 Coaxial Cable

23

⎟⎠⎞

⎜⎝⎛=

abln

2πµ

l

⎟⎠⎞

⎜⎝⎛==

ab

CZ ln

21

0 εµ

πl

( )abC

ln2πε

=

However, this kind of cable is difficult to fix into PCB board compare to the

microstrip line. Thus, coaxial cable is not suitable for this project. Here are some

formulas which related to coaxial cable.

The line inductance ( l ) of coaxial cable is [5],

The capacitor per unit length of coaxial cable is [5],

The characteristic impedance (Z0) of a coaxial cable is [5],

Whereas ε, µ the permeability and permittivity of the filling respectively.

3.3.2 Microstrip Transmission Line

The microstrip transmission line is the most commonly used Microwave

Integrated Circuit (MIC) transmission medium and is also one of the most popular

type of planar transmission line. A planar configuration implies that the dimensions

in a single plane can determine the characteristics of the element. For example, the

width, w, of a microstrip line on a dielectric substrate can be adjusted to control its

impedance.

(3.2)

(3.1)

(3.3)

24

The structure of a microstrip transmission line is shown in the figure 3.6. The

most important dimension parameters of a microstrip circuit design are the width, w,

of the microstrip line and the height, h, which is equivalent to the thickness of the

dielectric substrate [6]. The relative permittivity, εr, of the substrate is also another

important parameter. The fabrication of a microstrip transmission line is often done

through etching on a microwave substrate material.

Figure 3.6 Structure of Microstrip Transmission Line

The thickness of the strip, t, and the conductivity, σ are not important

parameters and are often neglected.

3.4 Substrate Materials

Dielectric substrate plays an important role in the design and simulation of

the microstrip transmission line as well as any other antennas. Some important

dimensions of the dielectric substrate are:

• The dielectric constant.

• The dielectric loss tangent that sets the dielectric loss.

25

• The cost.

• The thickness of the copper surface.

There are numerous types of substrates that can be used for the design of

antennas. They often have different characteristics and their dielectric constants

normally range from 2.2 ≤ rε ≤12. Thick substrates with low relative dielectric

constants are often used as they provide better efficiency and a wider bandwidth.

However, using thin substrates with high dielectric constant would result in smaller

antenna size. But this also results negatively on the efficiency and bandwidth.

Therefore, there must be a design trade-off between antenna size and good antenna

performance.

3.5 Microstrip Transmission Line Design Formulas

To design a microstrip transmission line, first must be able to obtain

dimensions such as effective dielectric constant, wavelength and characteristic

impedance.

3.5.1 Effective Dielectric Constant

One might think that the effective dielectric constant, ∑r,eff, is the same as the

dielectric constant, ∑r, of the substrate. This appears to be true only for a

homogeneous structure and not for a non-homogeneous structure. For microstrip

structures, we are able to calculate the effective dielectric constant that comes in two

26

different cases. These two cases are illustrated in figure 3.7 whereby the top diagram

shows a microstrip with width, w, greater than the thickness, h, of the substrate

(wεh). The microstrip with thickness greater than width is at the bottom diagram [6].

Figure 3.7: Wide and Narrow (Width) Microstrip Line

The effective dielectric constant of a microstrip line is given by approximated by [7]:

( ) reffrr εεε ≤≤+ ,121 (3.4)

1104.01212

12

1 221

, ≤⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡

⎟⎠⎞

⎜⎝⎛ −+⎟

⎟

⎠

⎞

⎜⎜

⎝

⎛+

−+

+=

hwfor

hw

hw

rreffr

εεε (3.5)

11212

12

12

1

, ≥⎟⎟

⎠

⎞

⎜⎜

⎝

⎛+

−+

+=

hwfor

hw

rreffr

εεε (3.6)

27

3.5.2 Wavelength

For a propagating wave in free space, the wavelength of that medium is equal

to the speed of light divided by its operating frequency. To obtain the wavelength of

a given wave-guide or antenna, the free space wavelength is simply divided by the

square root of the effective dielectric constant of the wave-guide. These are shown in

equations (3.7) and (3.8) [7].

o

o fc

=λ (3.7)

effr

og

,ελλ = (3.8)

Where c = speed of light, fo = operating frequency, oλ = free space

wavelength and gλ = the guide wavelength.

3.5.3 Characteristic Impedance

The characteristic impedance, Zo, of any line is the function of its geometry

and dielectric constant. For a microstrip transmission line, the characteristic

impedance is defined as the ratio of voltage and current of a travelling wave. For a

microstrip line with width, w, we are able to calculate the characteristic impedance

through the following two equations [7]:

125.08ln60

,

≤⎟⎟

⎠

⎞

⎜⎜

⎝

⎛+=

hwfor

hw

hwZ

effro ε

(3.9)

28

( ) 1444.1ln667.0393.1

120, ≥

+++=

hwfor

hw

hwZ effr

o

επ

(3.10)

3.5.4 Synthesis Equations

The width-to-height (w/h) is a strong function of Z0 and of the substrate

permittivity εr. In addition, the characteristic impedance of a microstrip transmission

line is also related to its width. As for the length of the line, it does not have much

significance on the impedance characteristics. Hence, various formulas had been

derived for microstrip calculations [7]. Wheeler developed this formula according to

the relationship of the line width with its characteristic impedance and substrate

permittivity.

2)'2exp(

'exp8−

=H

Hhw (3.10)

Where

⎟⎟⎠

⎞⎜⎜⎝

⎛+⎟⎟

⎠

⎞⎜⎜⎝

⎛+−

++

=πε

πεεε 4ln1

2ln

11

21

120)1(2

'rr

rroZH (3.11)

However, if the characteristic impedance Z0 < 44 - 2 rε , the ratio of the width of

the microstrip line and the dielectric thickness is given by

( ) ( )[ ] ( ) ⎥⎦

⎤⎢⎣

⎡−+−

−+−−−=

rr

r dddhw

επεε

π εεε517.0293.01ln

112ln12 (3.12)

Where

roZ

dε

πε

260= (3.13)

29

W

L

Figure 3.8 Rectangular Patch

3.6 Design of Rectangular Microstrip Antenna

Element Width and Length

With a larger patch width the radiated power will increased and resonant

resistance will decreased, bandwidth will increase and it will also increased radiation

efficiency. With a proper excitation one may choose a patch width W greater than the

patch length L without undesired modes. It have been suggested that 1< W/L <2 [8].

Practical width that leads to a good radiation efficiencies [8]:

The effective dielectric constant can be computed from equation as shown below [8]:

The actual length of the patch can now be determined by the followed equation [8]:

( )[ ]r

r

fcW

21/2 2

1+

=ε (3.14)

Lf

cLeffr

∆−= 22 ε

(3.16)

( ) ( )( ) ⎥⎦⎤

⎢⎣⎡ +−++=

− 21

1211121

Wh

rreff εεε(3.15)

1>h

Wfor

30

813.0/264.0/

258.0300.0

412.0++

−

+=∆

hWhWhL

eff

eff

εε (3.17)

31

CHAPTER 4

ANTENNA DESIGN AND PROCEDURES

4.1 Introduction

Figure 4.1 Work Flow

This project requires plenty of researches and trials. To have a strong

background of antenna design, studies and analysis have to be done beforehand.

Research on microstrip multi-band antenna has to be completed to have a clear

32

picture on the overall designing process. The factors that will influence the

performance of the antenna have to be determined and further investigate on their

effects. Then, analysis has to be performed on various antenna designs that are

suitable to be implemented in the project.

For the design of this project, there are some aspects that need extra attention,

such as:

• The return loss of the antenna has to fall on 0.9GHz, 1.8GHz,

1.9GHz, 2GHz and 2.4GHz, which is able to provide good

performance

• The bandwidth of the antenna has to be sufficient enough to

support the required frequency

This project requires a lot of simulations to be done. Hence, being able to

familiar with the Microwave Office simulation software is essential. Apart from that,

being able to use all the related measurement tools in the Wireless Communication

Centre Laboratory is very important as well. For example, being able to use the

Marconi Test Equipment is important for the measurement on return loss.

In brief, the objectives of this project can be achieved by implementing the

following steps as shown in the Figure 4.1.

33

4.2 Starting Point

At the initial stage of antenna design, an IEEE paper “A Low-Profile Planar

Monopole Antenna for Multiband Operation of Mobile Handsets” [9] is referred

and is set as the primary reference.

Figure 4.2 Geometry and dimensions of the proposed low-profile planar monopole

antenna for GSM/DCS/PCS/UMTS operation

Figure 4.2 shows the proposed low-profile planar monopole antenna which

could operate at the global system for mobile communication (890–960 MHz),

digital communication system (1710–1880 MHz), personal communication system

(1850–1990 MHz), and universal mobile telecommunication system (1920–2170

MHz) bands. The radiating element is a rectangular patch with a folded slit inserted

at its bottom edge, and is printed on an inexpensive FR4 substrate (thickness 0.4 mm,

relative permittivity 4.4) as shown in the figure. A 50- microstrip line is used to feed

the monopole antenna, and is printed on the same substrate. On the other side of the

substrate, there is a ground plane below the microstrip feed line. This ground plane

34

was selected to be 30x60 mm2 in the experiment, which can be considered to be the

ground plane of a practical mobile handset.

The radiating rectangular patch has dimensions of 10x30 mm2 and is placed

on top of the ground plane with a distance of 2 mm. The dimensions of the folded

inserted slit are shown in the figure. The major effect of the folded slit is to separate

the rectangular patch into two sub-patches, one smaller inner sub-patch and one

larger outer sub-patch. It should be noted that the open end of the folded slit at the

patch’s bottom edge is placed close to the feed point, and the other end inside the

patch is also designed to be close to the feed point. In this case, the smaller inner sub-

patch is encircled by the outer one, which leads to two possible excited surface

current paths inside the rectangular patch. The longer path starts from the feed point

and follows the folded slit to the open end of the slit at the patch’s bottom edge,

while the shorter one is from the feed point to the end of the inner sub-patch

encircled by the folded slit. It can be seen that the length of the longer path is much

greater than the length of the rectangular patch, which makes the fundamental

resonant frequency of the proposed antenna greatly lowered. In the proposed design

shown in Figure 4.1, this length is about 70 mm, which is slightly less than one-

quarter wavelength of the operating frequency at 900 MHz. This difference is largely

due to the effect of the supporting FR4 substrate, which reduces the resonant length

of the radiating element [10].

On the other hand, the length of the shorter path in the proposed design is

about 30 mm, which makes it possible for the excitation of a quarter-wavelength

resonant mode at about 2000 MHz. This resonant mode incorporating the second-

higher (half-wavelength) resonant mode of the longer path, which is expected to be

at about 1800 MHz, forms a wide impedance bandwidth covering the bandwidths of

the 1800-, 1900-, and 2050-MHz bands for the proposed antenna.

35

Figure 4.3 Measured and simulated return loss for the proposed antenna

Figure 4.3 shows the measured return loss of the proposed antenna. It is

clearly seen that two wide operating bandwidths are obtained. The lower bandwidth,

determined by 1: 2.5 VSWR, reaches 142 MHz and covers the GSM band (890–960

MHz). On the other hand, the upper band has a bandwidth as large as 565 MHz and

covers the DCS (1710–1880 MHz), PCS (1850–1990 MHz), and UMTS (1920–2170

MHz) bands. The measured data in general agree with the simulated results.

Figure 4.4 Simulated IE3D results of the surface current distributions on the

radiating patch for the proposed antenna at 900, 1800, 1900, and

2050 MHz.

36

The excited surface current distributions, obtained from the IE3D simulation,

on the radiating patch for the proposed antenna at 900, 1800, 1900, and 2050 MHz

are also presented in Figure 4.4. For the 900-MHz excitation, a larger surface current

distribution observed for the longer path along the outer sub-patch. This suggests that

the outer sub-patch is the major radiating element for the proposed antenna at the

900-MHz band, and the outer sub-patch is operated as a quarter-wavelength structure.

For the 1800-, 1900-, and 2050-MHz operation, it is observed that the surface current

distribution in the inner sub-patch gradually increases. This also indicates that the

inner sub-patch is the major radiating element for the higher operating frequencies of

the antenna’s upper band, especially in the 2050-MHz band, and is also operated as a

quarter-wavelength structure. As for the lower operating frequencies of the antenna’s

upper band, it is largely related to the outer sub-patch operated as a half-wavelength

structure. This can be explained that the current distributions in the outer sub-patch

are larger for the 1800- and 1900-MHz operations than for the 2050-MHz operation.

Figure 4.5 Measured radiation patterns for the proposed antenna at:

(a) 900 MHz and (b) 1800 MHz

37

Figure 4.6 Measured radiation patterns for the proposed antenna at:

(a) 1900 MHz and (b) 2050 MHz

Figure 4.5 and 4.6 plot the measured radiation patterns in the xy plane

(azimuthal direction) and yz plane (elevation direction) for the proposed antenna at

900, 1800, 1900, and 2050 MHz. Although the obtained radiation patterns are not as

good as those of a conventional simple monopole antenna having a very good

azimuthal omni-directional pattern and null radiation along the antenna axis ( =0°),

the proposed antenna in general shows a monopole-like radiation pattern.

38

(a) (b)

(c) (d)

Figure 4.7 Measured antenna gain for the proposed antenna.

(a) The GSM band (890–960 MHz).

(b) The DCS band (1710–1880 MHz).

(c) The PCS band (1850–1990 MHz).

(d) The UMTS band (1920–2170 MHz).

Figure 4.7 shows the measured antenna gain against frequency for the

proposed antenna. For the 900-MHz band, a peak antenna gain of about 2.9 dB is

observed, with gain variations less than 1.5 dB. For the 1800-, 1900-, and 2050-MHz

bands, the peak antenna gain observed is 3.0, 3.4, and 3.4 dB, respectively, and the

gain variations are also less than 1.5 dB.

39

4.3 The Proposed Antenna Design

4.3.1 The Design Specifications

The proposed antenna design was chosen as the basis as it is able to facilitate

multi-band operations. Thus, as our objective in the operation frequency bands is to

able to operate at

• GSM-900 ( Global System for Mobile Communications, 880-960 MHz)

• DSC-1800 ( Digital Communication System, 1710-1880 MHz)

• PCS-1900 (Personal Communication Services, 1850-1990MHz)

• UMTS-2000 ( Universal Mobile Telecommunication System, 1920-

2170MHz)

At the first stage of work, concentration will be on DCS-1800, PCS-1900 and

UMTS-2000 where

• f01 = 1.8 GHz

• f02 = 1.9 GHz

• f03 = 2 GHz

At the second stage of work, the antenna would be concentrate to other

frequency bands like

• f04 = 0.9 GHz

• f05 = 1.575 GHz

• f06 = 2.4 GHz

40

Besides, the specifications for FR4 substrate are as below:

• Dielectric constant, rε =4.7

• Height, h= 1.6mm

• Loss tangent = 0.019

4.3.2 Antenna Structure

The proposed antenna for this project is shown in figure 4.8. Compared with

the low-profile planar monopole antenna in figure 4.2, the dimensions of the antenna

have been change in the result of the thickness of the FR4 substrate available in

laboratory is 1.6mm while in the proposed design the thickness of the FR4 substrate

is 0.4mm. The changes in dimensions are made because the effect of varies

thickness of the substrate cannot be negligible.

In order to start develop the rectangular patch antenna, the dimension of

width, W and length, L with the substrate thickness 1.6mm is calculated using the

formula stated in last chapter. The calculations are as below:

41

i) For Radiating Patch

(3.14)

-0.5

(3.15)

= -0.5

=2.789

Extended increment length,

(3.17)

Actual length,

(3.16) / (2x1.9Gx -2(0.79)

=47.2mm-1.58mm

= 45.62mm

ii) For inner sub-patch and

outer sub-patch

For low frequency,

(For outer sub-patch)

Resonant frequency, fr = 900 MHz

oo f

c=λ

= 0.3333m

= 333.33mm

oλ = 83.33mm

84mm

For high frequency,

(For inner sub-patch)

Resonant frequency, fr = 1.9 GHz

oo f

c=λ

oλ = 39.47mm

40mm

42

From the calculation, the width of the radiating patch is W=48mm, while

the length of the radiating patch is L= 46mm. The new proposed antenna design is

shown in figure 4.8.

Figure 4.8 Proposed Multi-band Microstrip Antenna (Design 1)

Meanwhile, several designs are proposed. This is to compare the performance

of each design. Figure 4.9 and 4.10 are design by changing the location of the

transmission line. The dimensions of the radiating path keep unchanged.


Ground

Ground

43


On the other hand, an effort of shorten the inner sub-patch have been done in

order to show the effect of dimension changed. The design is shown in figure 4.11

and 4.12.


Ground

Ground

44


Beside the above five designs which have changes in location of the

transmission line and the dimensions of the inner sub-patch, figure 4.13 show

another design which has a fix 3mm in width for its transmission line and radiating

path.


Ground

Ground

45

4.4 The Simulation Software

Microwave Office is used as the principle electromagnetic simulation

software package for designing the antenna for this project. Furthermore, verify the

operation of the antenna at the prescribed frequencies in term of return loss and

radiation pattern.

4.5 The Fabrication Process

After finalization of the designs, fabrication process took place to produce the

prototypes. The top patch of the antenna is made from FR4, where etching process is

needed to remove unwanted portion of the copper layer. Lastly, a 50ohm SMA

connector is used to feed the antenna.

The fabrication process of the antennas needs extra attention as slight changes

of the parameters will affect the overall performance of the antennas. The fabrication

process involved laminator thermal transfer process, etching and soldering. Figure

4.14 shows the etching machine used in the fabrication process.

Human errors during fabrication such as inaccurate dimensioning, imperfect

etching and improper soldering are the major cause of frequency shifting. A slight

difference of 0.5mm will result in very much difference in antenna performance.

46

Figure 4.14 Etching Machine

4.6 The Measurement Stage

After the fabrication process, measurement is done to collect required data

such as return loss. The return loss of the antenna is measured using Marconi

Instrument in Wireless Communication Laboratory.

Figure 4.15 Marconi Test Equipment

CHAPTER 5

RESULTS AND DISCUSSION

5.1 Introduction

The fundamental aim of this project is to produce the antenna which could

cover several frequency bands. Previously, monopole antenna design was adapted.

With the demand for compact handheld communication devices have grown

significantly, build-in microstrip antenna design is applied for the miniaturization

and to provide good coverage of the device.

The performance of the antennas were analyzed in two different ways, first is

the simulations results and then the measured results.

Microwave Office is a powerful simulation tool that is able to generate not

only return loss but the radiation pattern as well. Therefore, to verify the antenna

designs, simulations are done beforehand. The return loss generated in Microwave

Office was then compared with the measured results.

48

5.2 Return Loss

5.2.1 The Simulation Return Loss

In telecommunication, return loss is the ratio, at the junction of a transmission

line and terminating impedance or other discontinuity, of the amplitude of the

reflected wave to the amplitude of the incident wave. The return loss value describes

the reduction in the amplitude of the reflected energy, as compared to the forward

energy.

For antenna, return loss have to be as small as possible in the operating

frequency range. A value of less than -10dB (which is mean 10 percent of the total

power has been reflected and 90 percent of the total power has been transmitted) is

required for good performance.

Figure 5.1 The Simulated Return Loss for Designed Antenna (Design1)

49



50



51


Table 5.1 Comparison of Return Loss between the six proposed antenna designs

S11

0.9GHz 1.575GHz 1.8GHz 1.9GHz 2GHz 2.4GHz

dB dB dB dB dB dB

Design1 -13.18 -11.33 -11.02 -10.69 -10.84 -14.25

Design2 -14.41 -15.66 -12.96 -13.23 -14.21 -15.85

Design3 -11.23 -13.65 -16.98 -17.69 -18.66 -21.35

Design4 -13.94 -13.44 -17.42 -21.87 -25.51 -20.18

Design5 -15.19 -12.86 -15.95 -19.58 -23.88 -20.98

Design6 -5.121 -13.49 -7.808 -9.555 -12.69 -11.28

From table 5.1, it could clearly see that Design 1 until Design5 give a return

loss below -10dB (SWR=2) for all the frequency bands such as 0.9GHz, 1.575GHz,

1.8GHZ, 1.9GHz, 2GHz and 2.4GHz. For Design6, it gives a return loss below -8dB

52

where it has approximately 15 percent of the total power has been reflected.

Therefore, the power that transmitted using Design6 is definitely lower than the

power transmitted using the other five designs proposed.

The different in antenna design structure for Design1 and Design2 is just the

location of the transmission line where the transmission line for Design 1 is located

at the left while in Design2; it has been change to the right side. Thus, signal is fed

into the radiating path through the edge of the transmission line. In the view for

return loss, Design gives a better performance compared to Design1. As from the

simulation results, Design2 has the deeper valley, which leads Design2 to have a

greater value in return loss.

Design structure of Design1, Design2 and Design3 basically are the same as

they are having the same radiating patch dimension except the location and the

structure of the transmission line. Referring the simulation result obtained, Design 3

is the best design among these three designs. This is due to it having the greatest

return loss value, where the greater the value of the return loss, the better the device

will perform; most of the power will be transmitted. Thus, Design3 will be having

the least percentage of the power reflected at the higher frequency (1.8GHz, 1.9GHz,

2GHz and 2.4GHz). As for the lower frequency bands (0.9GHz and 1.575GHz),

Design 2 perform better compared to others.

Basically, Design1, 2, and 3 fulfilled the requirement of -10dB in their return

loss. These three designs could be operate at all the frequency bands (GSM, GPS,

DCS, PCS, UMTS and WLAN), where it achieved the specifications of this project.

In the other hand, if the system operates frequently at the lower frequency, it is

suggested Design 2 is used as the design perform well at the lower frequency. Design

3 is preferable to operate at higher frequency, as it will give a promising return loss.

53

Design4 and Design5 are the designs that proposed with a shorter inner path.

Compared to Design1, 2 and 3, obviously Design4 and 5 have better performance in

return loss. Generally, Design4 and 5 work well in all the frequency bands. Design4

have stable performance in return loss through out the frequency band. In details,

antenna with Design5 performed better at the lower frequency while antenna with

Design4 performs well at higher frequency.

For antenna with Design6, at frequency 0.9GHZ, 1.8GHz and 1.9GHz, it

gives a return loss range between -8dB and -10dB. At these frequency bands, the

power reflected increase to 15 percent, where only 85 percent of the power is being

transmitted. But, at 1.575GHz, 2GHz and 2.4GHz, the return loss obtained is -

13.49dB, -12.69dB and -11.28dB; Overall, Design6 still not having a good

performance in return loss, thus some modification still needed.

Since all of the proposed antennas presented well in the return loss, Design1,

Design3 and Design6 are chosen to be fabricated.

5.2.2 The Measured Return Loss

Two sets of antennas have been fabricated. The first set is fabricated using

copper tape while second set is fabricated by etching. Each set consists three

antennas: Design1, Design3 and Design6; thus, six antennas have been fabricated.

The measurements on return loss have been done by using Marconi Test Equipment

in Wireless Communication Center (WCC).

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5.2.2.1 The Measured Return Loss of Antenna (Set One)

Set one antenna is fabricated using single sided board where the adhesive

copper tape is used to form the radiating patch at the side without copper surface

while the ground plane is obtained through etching the copper surface. The results of

the return loss are as follows:

Figure 5.7 The Measured Return Loss (Set One Design1)

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The return loss value for Design1 and Design3 range between-1dB and -5dB,

which indicate a poor return loss for this set of antenna where almost 50 percent of

the power has been reflected. Thus, this set of prototype antenna is not suitable for

practical use. From the measured result for the Design6, its shows almost 0dB at all

56

of the frequency that this antenna should cover for, which indicate that all of the

power that transmits is being reflected.

From the experimental findings, the measured results are un-complying with

the simulation results. This would caused by the inaccurate dimensions of the

antenna size and the dimensions of the radiating path. Besides, the soldering point

that meant to join the edge of the copper tape causing some discontinuity, thus, it

contribute some losses to the antenna. Moreover, aluminum SMA connectors are

used in this prototype, which it is less conductive than copper SMA connectors are

another factor that leads to the un-complying results.

Since measured return loss for the antennas fabricated are un-complying,

another set of antenna (Set Two) is fabricated in order to obtain a better return loss.

5.2.2.2 The Measured Return Loss of Antenna (Set Two)

Set two antenna is fabricated using copper SMA connectors and by etching

the copper surface of the double sided board for the radiating patch and the ground

plane. The results of the return loss for the re-fabricated antennas are as follows:

57

Figure 5.10 The Measured Return Loss (Set Two Design1)


3.1GHz -17.07dB

3.8GHz -12.75dB

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The measured return loss for all of the designs has the graph contour similar

to the simulation return loss. For overall performance, the measured return losses for

set two antenna have some improvement.

From Figure 5.10, the measured return loss for Design1, although do not have

satisfy result at 0.9GHz, 1.8GHz, 1.9GHZ, 2GHz and 2.4GHZ, but good return loss

are obtained at 1.5Hz, 3.1GHz and 3.8GHz which gives -9.60dB, -17.07dB and -

12.75dB respectively. The same condition happens for Design3, where the measured

result has good return loss at 1.6GHz, 3.1GHz and 3.2GHz. While Design6 have a

good value for return loss -11.63dB at 2GHz, and an extremely good return loss -

21.27dB at 3.7GHz where only one percent of the power being reflected.

The measured result of the set two antenna clearly showed that frequency

shifting occurred. All the graphs showed the frequency is shifted to the right.

Impedance matching is the main factor that contribute to the frequency shifting,

where the antenna are not match properly. Moreover, inaccurate dimension of the

antenna and the improper etching would also contribute some losses.

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From the Return Loss simulations, the graph contour for Design1 and

Design2 indicates a wide-bandwidth property, while Design3 depicts a multiband

property. Thus, it can be inferred that the width of patch renders a wide-bandwidth.

5.3 Radiation Pattern

The radiation pattern is a graphical depiction of the relative field strength

transmitted from or received by the antenna. Antenna radiation patterns are taken at

one frequency, one polarization, and one plane cut. The patterns are usually

presented in polar or rectilinear form with a dB strength scale. Patterns are

normalized to the maximum graph value, 0 dB, and directivity is given for the

antenna.

The radiation pattern for the chosen fabricated designs are obtained and shown in the figures below:

Figure 5.13 The Radiation Pattern for 1.8 GHz Band (Design1)

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61

Most of the radiation patterns give an Omni-directional radiation, which

indicate the radiation is in all the directions; the signal radiate backward and front. It

is desirable for mobile application due to most of the receiving signal come from all

the directions.

5.4 Antennas Prototype

The fabrication process is very complex as any tiny shift in the fabrication

will shift the resonant frequency. Besides, return loss which is the parameter to

determine the multi-band that allow the antenna to operate at certain band, is very

sensitive to the dimension changes. Moreover, the sharpness at the cutting edge of

the patch and antenna also would cause some discrepancy in the return loss

measured.

The antennas have been fabricated successfully with the results as discussed

in previous section, figures below show the prototype of the set one and set two

fabricated antennas.

Figure 5.16 The Fabricated Antenna Design1 (Set One)

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Figure 5.19 The Fabricated Antenna Design1 (Set Two)

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CHAPTER 6

CONCLUSIONS AND RECOMMENDATIONS

6.1 Conclusions

The success and rapid growth of cellular system has been foremost in

establishing a critical need for design technique that will greatly increase mobile

communication capacity and flexibility, to deliver the new much sought-after

services. To meet these critical needs system designer have made advances on many

research front such as improve techniques for efficient signal processing, more

precise propagation predication methods, and physically compact and higher

performance antenna to improve all possible areas of the performance of mobile

phones. As mobile phones continue to shrink in size, there is an overwhelming need

to miniaturize and improve the performance of the antenna. Microstrip antennas help

to address the above concerns.

However, antenna design techniques, such as developing an antenna that can

operate at multiple frequencies as well as being conformal in design, offer some

potential in further dealing with the deficiencies of the modern mobile phone

antenna. The purpose of this thesis was to develop a multi-band microstrip antenna

and investigate the effects of conformality on the antenna.

65

The main objective of this thesis is achieved with new antennas designed that

operate at four frequency band where it can be integrated with any handheld devices

given its low profile and small size characteristics. This has been done through a very

complex and time-consuming process where the problems were faces constantly. In

this thesis, the microstrip multiband antenna has been analyzed both theoretically and

experimentally through computer simulations and hardware measurement.

The multiband and wide-bandwidth antennas for mobile handset which would

operate in different frequency bands has been proposed and fabricated. And, the

antennas have been successfully implemented, though discrepancies occur between

simulated and measured results.

6.2 Recommendations for the future work

The future work is proposed to have further improvement in the antenna

performance. There are discrepancies between simulated and measured results are

caused by human errors that might occur during fabrication processes. Thus, further

development is needed to further improve the fabrication processes. The fabrication

process may involve laminator thermal transfer process, etching and soldering.

Besides, a few of prototypes should be fabricated in order to get a good result

in the measurement of the antenna as it is difficult to get a good result in just a

fabrication process; experience and knowledge is needed.

66

Moreover, in the future, the antenna can be developing for tracking system

application such as GPS which operate at 1.575GHz.

REFERENCES

[1] K.L.Wong, Design of Nonplanar Microstrip Antennas and Transmission

Lines, JohnWiley & Sons, New York, NY, 1999.

[2] K.L.Wong, Comapct and Broadband Microstrip Antenna, JohnWiley & Sons,

New York, USA, 2002.

[3] IEEE Transactions on Antenns and Propagations, vols. AP-17, No. 3, May

1969; AP-22, No.1, January 1974; and AP-31, No.6, Part II, November 1983.

[4] Bahl, I.J. and Bhartia, P. (1980). “Microstrip Antenna.” Dedham,

Massachusetts: Artech House Inc.

[5] Allan W. S., "Understanding Microwave," Second Edition, New York, John

Wiley & Sons, Inc., 1993.

[6] Teng P. L., and Wong K. L., "Planar Monopole Folded into a Compact

Structure for Very Low Profile Multi-band Mobile Phone Antenna," Microwave Opt.

Technol. Lett., vol. 33, pp. 22-25, April 5, 2002.

[7] Pozar D., "Microwave Engineering," Second Edition, New York, John Wiley

& Sons, Inc., 1998.

[8] Balanis C., "Antenna Theory Analysis and Design," Second Edition, United

Stated, John Wiley & Sons, Inc., 1997.

68

[9] Kin-Lu Wong, Gwo_Yun Lee, Tzung-Wern Chiou, “A Low-Profile Planar

Monopole Antenna for Multiband Operation of Mobile Handsets”, IEEE

Transcations on Antenna and Propagation, Vol. 51, No.1, January 2003.

[10] E. Lee, P. S. Hall, and P. Gardner, “Compact Wideband Planar Monopole

Antenna,” Electron. Lett., vol. 35, pp. 2157–2158, Dec. 1999.

[11] Xu Jing, Zhengwei Du andKe Gong, “A Compact Multiband Planar Antenna

for Mobile Handsets”

[12] P. P. Hammoud and F. Colonel, “Matching The Input Impedance of A

Broadband Disc Monopole ”, Electron. Lett, vol.29, pp. 406-407, Feb. 1993.

[13] E. Lee, P. S. Hall, and P. Gardner, “Dual Band Folder Monopole/Loop

Antenna for Terrestrial Communication System”, Electron. Lett, vol.36, pp. 1990-

1991, Nov 2000.

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APPENDIX A

DESIGNING PROCEDURES USING MICROWAVE OFFICE

1. Right click the EM structure to open a new EM structure.

2. Enter a name for the EM structure, and click the ‘create’ button.

3. Click the ‘enclosure’, to enter the substrate information.

Change the tab to enter parameter for dielectric layer and boundaries.

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4. Use Rectangular Conductor to draw the rectangular patch or ground plane.

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5. To simulate the return loss, create a graph and select Rectangular graph type.

Right click the graph name to add return loss measurement.

6. To enter the frequency of the simulation, use Project Option.

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7. Click the Analyze icon to simulate the return loss for this antenna design.

8. Finally, the simulation window will come out. The result will be display once

the simulation is finished.

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APPENDIX B

RETURN LOSS MEASUREMENT

Design1 (Set One) Design3 (Set One)

Design6 (Set One)

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Design1 (Set Two) Design3 (Set Two)

Design6 (Set Two)

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APPENDIX C

C.1 Equipment Used for Antenna Testing

Marconi Test Equipment

76

C.2 Equipment Used for PCB Fabrication

Etching Machine

Laminator Thermal Transfer Machine PCB Cutting Equipment

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APPENDIX D

COMPONENTS AND PRICE LIST

There are components that are not available in the laboratory and in Store FKE,

below are the components that have ordered for the fabrication of the antenna

designs.

Company Address Component Price per

piece

Quantity RM

Farnell (M)

Sdn. Bhd.

http:

//my.farnell.com

SMA

Connector

RM 14

RM 30

3

3

42

90

Copper Tape RM 70.50 1 70.50

TOTAL 202.50

a multi-band microstrip antenna for mobile...

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