A MULTI-BAND MICROSTRIP ANTENNA FOR MOBILE HANDSET TAN ZEE YEAN UNIVERSITI TEKNOLOGI MALAYSIA

Transcription

1 A MULTI-BAND MICROSTRIP ANTENNA FOR MOBILE HANDSET TAN ZEE YEAN UNIVERSITI TEKNOLOGI MALAYSIA

2 UNIVERSITI TEKNOLOGI MALAYSIA PSZ 19:16 (Pind. 1/97) 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 ) SULIT TERHAD (Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972) (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan) TIDAK TERHAD Disahkan oleh (TANDATANGAN PENULIS) (TANDATANGAN PENYELIA) Alamat Tetap: 58, KAMPUNG BARU, SEMELING, BEDONG, KEDAH. Nama Penyelia DR. NORHISHAM BIN HJ KHAMIS 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).

3 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

4 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

5 ii 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

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

7 iv 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.

8 v 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; MHz) band, centered at 900 MHz; the Digital Communication System (DCS; MHz) band, centered at 1800 MHz; and the Personal Communication System (PCS; MHz) band, centered at 1900 MHz and the Universal Mobile Telecommunication system (UMTS; MHz) band, centered at 2 GHz.

9 vi 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).

10 vii TABLE OF CONTENTS CHAPTER TITLE PAGE DECLARATION DEDICATION ACKNOWLEDGEMENTS ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS LIST OF APPENDENCES ii iii iv v vi vii x xi xiii xiv 1 INTRODUCTION Overview Problem Statement Objective Scope of Work Methodology Thesis Outline 6

11 viii 2 LITERATURE REVIEW Introduction From Analog to Digital Systems Antenna for Mobile Phones Microstrip Antenna Advantages and Disadvantages of 14 Microstrip Antennas Applications of Microstrip Antennas 15 3 THEORY OF MICROSTRIP PATCH ANTENNA Basic Characteristics of Microstrip Patch Antenna Analysis of Microstrip Fundamentals of Transmission Line Coaxial Cable Microstrip Transmission Line Substrate Materials Microstrip Transmission Line Design Formulas Effective Dielectric Constant Wavelength Characteristic Impedance Synthesis Equations Design of Rectangular Microstrip Antenna 29 4 ANTENNA DESIGN AND PROCEDURES Introduction Starting Point The Proposed Antenna Design The Design Specifications Antenna Structure The Simulation Software The Fabrication Process The Measurement Stage 46

12 ix 5 RESULTS AND DISCUSSION Introduction Return Loss The Simulation Return Loss The Measured Return Loss Set One Antenna Set Two Antenna Radiation Pattern Antenna Prototype 61 6 CONCLUSIONS Conclusions Recommendations for Future Work 65 REFERENCES 67 APPENDICES A-D 69-77

13 x LIST OF TABLES TABLE NO. TITLE PAGE 1.1 Frequency Bands for Wireless Applications Comparisons of Transmission Lines Comparison of Return Loss between the six proposed 51 antenna design

14 xi LIST OF FIGURES FIGURE NO. TITLE PAGE 1.1 Antenna Design and Development Flow Chart Microstrip Antenna Configurations Physical Structure of a Microstrip Patch Antenna Microstrip Patch Geometries Microstrip Line (Quasi-TEM Mode) Radiation Mechanism of Rectangular Microstrip Patch Coaxial Cable Structure of Microstrip Transmission Line Wide and Narrow (Width) Microstrip Line Rectangular Patch Work Flow 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 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 MHz and 1800 MHz 4.6 Measured radiation patterns for the proposed antenna at MHz and 2050 MHz 4.7 Measured antenna gain for the proposed antenna Proposed Multi-band Microstrip Antenna (Design 1) 42

15 xii 4.9 Proposed Multi-band Microstrip Antenna (Design 2) Proposed Multi-band Microstrip Antenna (Design 3) Proposed Multi-band Microstrip Antenna (Design 4) Proposed Multi-band Microstrip Antenna (Design 5) Proposed Multi-band Microstrip Antenna (Design 6) Etching Machine Marconi Test Equipment The Simulated Return Loss for Designed Antenna (Design1) The Simulated Return Loss for Designed Antenna (Design2) The Simulated Return Loss for Designed Antenna (Design3) The Simulated Return Loss for Designed Antenna (Design4) The Simulated Return Loss for Designed Antenna (Design5) The Simulated Return Loss for Designed Antenna (Design6) The Measured Return Loss (Set One Design1) The Measured Return Loss (Set One Design3) The Measured Return Loss (Set One Design6) The Measured Return Loss (Set Two Design1) The Measured Return Loss (Set Two Design3) The Measured Return Loss (Set Two Design6) The Radiation Pattern for 1.8GHz Band (Design1) The Radiation Pattern for 1.8GHz Band (Design3) The Radiation Pattern for 1.8GHz Band (Design6) The Fabricated Antenna Design1 (Set One) The Fabricated Antenna Design3 (Set One) The Fabricated Antenna Design6 (Set One) The Fabricated Antenna Design1 (Set Two) The Fabricated Antenna Design3 (Set Two) The Fabricated Antenna Design6 (Set Two) 63

16 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 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

17 xiv 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

18 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

19 2 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 triband 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 dualfrequency 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; MHz) band, centered at 900 MHz; the Digital Communication System (DCS; MHz) band, centered at 1800 MHz; and the Personal Communication System (PCS; MHz) band, centered at 1900 MHz and the Universal Mobile Telecommunication system (UMTS; MHz) band, centered at 2 GHz.

20 3 Table 1.1: Frequency bands for wireless applications Wireless Applications Frequency Bands (MHz) Global System for Mobile Communication GSM-900 Digital Communication System DCS Personal Communication System PCS Universal Mobile Telecommunication system UMTS-2000 Bluetooth and Wireless Local Area Network WLAN 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.

21 4 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 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.

22 5 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.

23 6 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.

24 7 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.

25 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 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

26 9 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 fourthgeneration (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.

27 10 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.

28 11 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

29 12 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 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 ) [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.

30 13 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 However, twenty years passed before practical antenna were fabricated, as better theoretical models and photo-etch techniques for copper or goldclad 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 ( ε 10 ), 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, ε r of r

31 14 the substrate should be low ( ε 2. 5), so as to enhance the fringe fields which account for the radiation. r Figure 2.1 Microstrip Antenna Configurations 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

32 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 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

33 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

34 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.

35 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.

36 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 ( ε 10 ) 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 ( ε 2. 5 ) to enhance fringing fields, which forms the basis of useful radiation in r 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. r

37 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 λ when the microstrip structure is about half a wavelength ( ) long, assuming no 2 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 λ phase as the patch line is ( ) long. This means that the far fields produced by 2 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 λ patch can be represented as two slots apart excited in phase and radiating in 2 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.

38 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:

39 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 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

40 23 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], l = µ ln 2π b a (3.1) The capacitor per unit length of coaxial cable is [5], 2πε C = ln ( b a) (3.2) The characteristic impedance (Z 0 ) of a coaxial cable is [5], Z 0 = l C = 1 2π µ b ln ε a (3.3) Whereas ε, µ the permeability and permittivity of the filling respectively 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.

41 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.

42 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 ε r 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 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

43 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]: ( ) r eff r r ε ε ε +, (3.4) , = h w for h w h w r r eff r ε ε ε (3.5) , = h w for h w r r eff r ε ε ε (3.6)

44 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]. c λ o = (3.7) f o λ o λ g = (3.8) ε r, eff Where c = speed of light, fo = operating frequency, λ o = free space wavelength and λ g = the guide wavelength 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]: Z o = 60 ε r, eff 8 ln w for w h h w h 1 (3.9)

45 28 Z o = w h 120π ε r, eff ln ( w ) h w for h 1 (3.10) Synthesis Equations The width-to-height (w/h) is a strong function of Z 0 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. Where w 8exp H ' = h exp(2h ') 2 (3.10) Z 2( ε r + 1) 1 ε r 1 π 1 4 H ' = o + ln + ln (3.11) ε r ε r π However, if the characteristic impedance Z0 < 44-2ε r, the ratio of the width of the microstrip line and the dielectric thickness is given by w h 2 = π ε r [( d 1) ln( 2d 1) ] + ln( d 1) ε ε πε r ε ε r (3.12) Where d ε 2 60π = (3.13) ε Z o r

46 Design of Rectangular Microstrip Antenna Element Width and Length W L Figure 3.8 Rectangular Patch 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]: W = c [ /( + 1) ] r ε (3.14) 2 f r The effective dielectric constant can be computed from equation as shown below [8]: W for h > 1 ε eff = ( ε + 1) + ( ε 1)( h ) 2 r r W (3.15) The actual length of the patch can now be determined by the followed equation [8]: L c = 2 L 2 f ε r eff (3.16)

47 30 ε L = 0.412h ε eff eff W / h W / h (3.17)

48 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

49 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.

50 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 ( MHz), digital communication system ( MHz), personal communication system ( MHz), and universal mobile telecommunication system ( 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

51 34 was selected to be 30x60 mm 2 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 mm 2 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 subpatch 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 onequarter 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 secondhigher (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.

52 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 ( MHz). On the other hand, the upper band has a bandwidth as large as 565 MHz and covers the DCS ( MHz), PCS ( MHz), and UMTS ( 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.

53 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 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

54 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.