MODELLING, SIMULATION AND ANALYSIS OF A SINGLE RECTANGULAR MICROSTRIP PATCH ANTENNA

CHARACTERISTIC

THELAHA BIN HAJI MASRI

A thesis submitted in full fulfillment of the requirements for the degree of

Master of Engineering

Faculty of Engineering UNIVERSITI MALAYSIA SARAWAK

2001

ACKNOWLEDGEMENT

First and foremost, thanks to almighty Allah for enabling the author to complete and achieve the objectives of this research. Also, the author is deeply indebted to the research supervisor, Associate Professor Dr. Mohamad Kadim Suaidi, whose encouragement, guidance and advice has helped the author in many ways for making this research a success.

Profound appreciation must also be expressed to the lab assistant, especially to Encik Wan Abu Bakar and Encik Zakaria Bin Idris for letting the author to use a few computers and some development tools essential for the study and simulation work. Their helps and support in times of troubles and difficulties is very much appreciated.

The author also would like to express his special thanks to the University of Malaysia Sarawak (UNIMAS) for their sponsorships and granting the author's study leave which made this work possible.

Last but not least, thanks to dearest colleague and friends especially to Encik Kismet Hong Ping, Cik Grace Quake and Cik Lisa Yong for their constructive suggestion. And finally to the author's family for their encouragement, patient and who have helped the author in their own ways, which enable him to see this thesis through to completion.

ABSTRACT

Shorter wavelength in the microwave region permits a simpler form of small and low profile type of

antenna to be produced, which, in this research includes an antenna that employs a printed circuit

construction including a microstrip element which is called microstrip patch antenna. Their non-

electrical characteristic, and the ease, with which a number of different feed network can be fabricated

in microstrip form, also makes microstrip patch antenna preferred over other types of radiators. The

lightweight construction and the suitability for integration with microwave integrated circuits are two

more of their numerous advantages. Additionally the simplicity of the structures makes this type of

antennas suitable for low-cost manufacturing.

This research investigated the microstrip patch antennas performance by studying and analyzing its

characteristics and parameters that makes the microstrip elements resonates and radiates microwave

signals into space. The literature, research, analysis and experiments through simulation is done

qualitatively, if not quantitatively, to the characteristics of a square or rectangular microstrip antennas.

This thesis also present some new ideas and ways in presenting the analysis, design techniques and

results of thi~~interesting and most developing topic in the antenna field, using Computer Aided

Design tools such as the MathCAD version 8.02 and Microwave Office 2000 (EM structures) version

3.2 simulating software.

ABSTRAK

Jarak gelombang yang pendek didalam julat gelombang mikro membolehkan sejenis antenna yang

lebih kecil dan ringan dibentuk. Antenna yang dimaksudkan itu yang dikaji didalam penyelidikan ini

termasuklah sejenis antenna yang dipanggil "Mikrostrip Patch Antenna" yang mana rekabentuk

asalnya berasaskan teknologi talian transmisi atas papan-litar. Sifat 'non-elektrikal'nya dan

kepelbagaian jenis talian suap yang mudah di fabrikasi dalam bentuk mikrostrip di atas papan litar

yang sama membuatkan antenna jenis ini disukai dan terpilih daripada pelbagai jenis d m bentuk

radiasi yang lain.

Rekabentuknya yang nngan dan kesesuaannya dllntegerasikan dengan htar-lltar benntegeras~

gelombang rmkro (MMIC) adalah antara keleb~han antenna mi. Tambahan lag1 bentuk 'patch' yang

nngkas membuatkan antenna In1 mudah & buat dan sesua untuk pengilangan.

Thesis ini membentangkan penyelidikan terhadap performance antenna mikrostrip dengan mengkaji

dan menganalisa karaktor dan parameter-parameter yang berkenaan yang membolehkannya

memancarkan maklumat ke udara. Kajian bertumpu secara kualitatif terhadap antenna yang berbentuk

segi-empat tepat ataupun segi-empat tak sama.

Thesis ini juga membentangkan kerja-kerja merekabentuk d m penganalisaan antenna yang amat sukar

difahami tersebut dl atas dengan gaya persembahan yang menarik dan mudah difahami. Ini dilakukan

dengan memapar gambara~ah-gambarajah teknikal yang menarik, aturcara yang sistematik dan

simulasi-simulasi menggunakan software MathCAD versi 8.0 d m Microwave Office versi 3.2..

List of Figures and IHustrations

FIGURE -

TITLE PAGE -

pyically controlled PIN 23

2.8 A slotted patch. 24 2.9 The bow-tie antenna, 24 2.10 The dual-folded dipole 26 2.11 A ring patch antenna for dual-frequency operation. 26 2. I2 The dichroic antenna. 28 2.13 A wedge-shaped patch antenna. 28 2.14 Front and exploded view of a Microstrip-line Feed 30 2.15 Front and exploded view of a Coaxial-Probe Feed 30 2.16a Front and exploded view of a Proximity-Coupled Feed 32 2.16b Front and exploded view of a Monolithic Proximity

coupling Feed 32 2.17 Front and exploded view of an Aperture-Coupled Feed 33

iv

Title - Figure

3.1

3.2

Geometrical configuration of a rectangular microstrip antenna - Approximation of the tangential field component I E, I near the edge of surface S The right -hand rules showing the direction of the field with respect to their corresponding unit vectors and fields involved

The variation of the electric field along the directions

perpendicular to the edge of the patch surface S

Field between the patch and the ground plane A rectangular patch geometry (rectangular cavity) diagram. E-field at the metallic surface of the patch antenna H-field, creating a perfect magnetic wall Configuration of the field of the two z-directed sources An aperture model of a rectangular MSA showing perspective view configuration, side view of the fringing fields and the top views of the four slots radiating elements (a) and also the continuous magnetic currents along the patch edge (b). Slot 1 configuration diagram A perspective view of a rectangular aperture diagram configuration for slot 1 (aperture positions for antenna analysis [5]) Top view of a rectangular aperture diagram configuration for slot 2 A perspective view of a rectangular aperture diagram configuration for slot 2 Top view of a rectangular aperture diagram configuration for slot 3 Top view of a rectangular aperture diagram configuration for slot 4 The coordinates of the four-slots of a Rectangular MSA with respect to the center of the patch antenna Geometry for the E and H-plane Experiment Flow Chart MathCAD simulation work sheet for calculating the Length and Width of a rectangular microstrip patch antenna. Cell Calculator Substrate information window - Noticed that the x and y divisions are fixed to 65 divisions

FIGURE TITLE - PAGE

4.5 Substrate information window - Dielectric Layers 11 1 4.6 Substrate information window - Boundaries 111 4.7 A 'Rectangular patch conductor' drawn on top of the

dielectric layer 113 4.8 Simulated results example 113 4.9 A comparison of the S l l Magnitude (a), S11 Phase (b),

S 11 Smith Chart and the VSWR < 2 curves between [I31 and simulated results from mw office 2000. 117

List of Tabie

TABLE - TITLE - PAGE

4.1 Statistical results , referred from Heriberto J. Delgado's papers entitled "Design of a lOGHz Rectangular Microstrip Patch Antenna Using HP Momentum" [8] and "Validation of Predicted WP MDS Momentum Input Impedance Data Using Measured Data for a Rectangular Patch Microstrip Antenna", [25] compared with Microwave Office 2000 for validation of works. 116

4.2 Data obtained based on configurations and dimensions of an optimum 10 GHz rectangular microstrip patch antenna gained from simulations using microwave office 2000. 118

PAGE

1

. . . 111

iv vi

1

1 2

2.3.4.7.3 Ring Patch Antenna 2.3.4.7.4 Dichroic Antenna 2.3.4.7.5 Wedge-Shape Antenna

2.3.5 Feeding Techniques 2.3.5.1 Microstrip-Line Feed 2.3.5.2 Coaxial-Probe Feed 2.3 S.3 Proximity-Coupled Feed 2.3.5.4 Aperture-Coupled Feed

2.3.6 Error Estimation 2.4 Conclusion

CHAPTER 3 THEORETICAL ANALYSIS OF THE RADIATION CHARACTERISTIC OF A SINGLE PATCH (RECTANGULAR) MICROSTRIP ANTENNA

A Rectangular Microstrip Antenna Modelled as a Four Element Slot Array A Rectangular Microstrip Antenna Approximation of the Fringing Fields Approximation of the Patch Fields Configuration (TM(mn) Mode - Using Cavity Models Taking into Consideration the Substrate's Dielectric and Thickness - Using Image Theory The Par Field Analysis - Using Aperture Model 3.6.1 Aperture Theory 3.6.2 Field Expression for Slot 1

3.6.2.1 Far-Field Expression for Slot 1

3.6.3 Field Expression for Slot 2 3.6.3.1 Far-Field Expression for Slot 2

3.6.4 Far-Field Expression for Slot 3 3.6.5 Far-Field Expression for Slot 4

Finding the Total Far-Field Radiation Expression - Using Linear Superposition. An Example of a TM (01) Mode Far-Field Radiation Pattern Equations of a Rectangular Microstrip Patch Antenna Co-Polarization and Cross-Polarization of the E-Plane and H-Plane Wave for the Rectangular Microstrip Patch Antenna 3.9.1 E-Plane Co-Polarisation and Cross-Polarisation 3.9.2 H-Plane Co-Polarization and Cross-Polarization. Fringing Fields

Resonant Frequencies For The TM rnn Mode Directivity Patch Surface Currents Simulation Program and Results Discussion and Conclusion

. . . V l l l

CHAPTER 4 AN ANALYSIS OF A RECTANGULAR MICROSTRIP PATCH ANTENNA USING MICROWAVE OFFICE 2000 VERSION 3.2 SOFTWARE

4.1 Introduction 4.2 MicroWave office 2000

4.2.1 EM Sight 4.3 Experiment Tips and Flow Chart 4.4 Experiment Set-up

4.4.1 Determining the Dimension of a 10 GHz Microstrip Antenna 4.4.2 Cells Calculator

4.4.2.1 Enclosure 4.4.2.2 Dielectric Layer 4.4.2.3 Boundaries

4.4.3 Drawing the Patch 4.4.4 Experiments and Investigations

4.4.4.1 Frequency of Operation 4.4.4.2 Material 4.4.4.3 Shapes 4.4.4.4 Feeding Techniques 4.4.4.5 Bandwidth Enhancement

4.4.5 Simulated Results Examples

4.5 Comparison With Other Researchers Work 4.6 Optimum Design for a Single Rectangular Microstrip Patch Antenna

using Microwave Office 2000 Software. 4.7 Conclusion

CHAPTER 5

References APPENDIX A APPENDIX B

APPENDIX C

APPENDIX D

APPENDIX E

DISCUSSION, RECOMMENDATIONS AND CONCLUSION

Discussion Recommendation 5.2.1 Future Works Conclusion

123 Microwave Materials - RT/duroid and Duroid 124 An Example on designing a single square and rectangular patch microstrip antenna using MathCAD version 8 Perturbed segmentation process (calculation) on a square and rectangular microstrip patch antennas: - An example and Integration formula (Nol) and (No 2) MathCAD simulation program for the radiation patterns of an arbitrary TM (rnn) mode of a single rectangular microstrip patch antenna. Experiments' results : - Using Microwave Office 2000 simulation software.

CHAPTER 1

INTRODUCTION

Portable radio equipment with a quarter-wavelength whip antenna can be a hindrance to handling. Antennas that stick out from handheld mobile telephone or from an automobile body are also undesirable from the design point of view. On a spacecraft, ships and tall buildings, various type antennas must be kept in a small area. Blocking and mutual interference between those antennas are serious problems. All this problems can be improved by making antennas small and conformable. With the recent advances in electronic devices such as the development of the GaAs-based pseudomorphic HEMT (high electron mobility transistor) and the GaAs heterojunction bipolar transistor (HBT), integrated circuits and their related electronics components has the possibility to operate at frequencies of over 100 GHz. Due to this developments, telecommunication equipment, especially in the field of wireless and mobile radio communication has rapidly reduced their physical size, but their antennas still remain large compared to the equipment itself.

There has been tremendous interest in the development of a small size, less weight, low cost, compact, and low profile antennas. This type of antenna must also be a readily mass- producible, high-aperture-efficiency antenna of useful bandwidth in which the radiator elements can be readily matched to a range of useful transmission line impedance for radiating and receiving a directional, linear polarised electromagnetic radiation beam. Such an antenna would be especially useful for low cost object sensing and microwave communications as mentioned above. Government and commercial applications also need similar applications especially in wireless LAN (PC, laptop etc,), high-performance aircraft, spacecraft, satellite, missile application and etc.

To meet these requirements, microstrip antenna [I] can be used. Their size, weight, cost, performance, ease of installation, compatible with MMIC components and aerodynamic profile suite the application requirements discussed above.

1.1 Historical Background

The microstrip antenna, a typical type of planar antenna, has now reached maturity, wherein only a few mysteries about its behaviour are still undiscovered. The original study of planar antennas, indeed, which utilises a stripline as a radiator or feeding system, began with the advent of the stripline by R. Barret [2] but it was certainly placed in the 1960s, with the first works published by Deschamps, Greig and Engleman, and Lewin, among others [3]. The research publications started to flow before 1970 with the appearance of the first design equations and in the mid-1970s, the invention of rnicrostrip antennas has been attributed to several authors such as Munson and Howell. Munson patented a microstrip element and Howell published data on basic rectangular and circular rnicrostrip antenna [3].

The early work by Munson on the development of this antenna for use as a low-profile flush-mounted antenna on rockets and missiles showed that this was a practical concept for use in many antenna system problems and thereby, gave birth to a new antenna industry.

1.2 Transmission Line

In an electronic system, power must be deIivered from a power source to a load and from component to component within that system. At the very low end of the microwave frequency region, two-wire lines are used to deliver power from its source to a load. In the intermediate microwave region and for short distance usage between circuits at higher frequencies, coaxial lines are used to advantage. At higher frequencies, a waveguide serves as the transmission lines and for interconnections between internal components, striplines and microstrips are used for transmission lines.

The design of microstrip antennas largely centres around the transmission line properties of the striplines and microstrip lines themselves. Due to this reason, it is important to understand their basic properties in order to understand and apply the principles of the antenna design based on microstrip transmission lines.

1.2.1 Stripline

A stripline or triplate device is a sandwich of three parallel conducting layers separated by a thin dielectric substrates, the centre conductor of which is analogous to the centre conductor of a coaxial transmission line. Stripline are used particularly for components such as couplers, hybrids and filters. The geometry of a stripline is shown in Figure l . la, and one can think of a stripline as a sort of "flattened out" coax and a sketch of the field lines is shown in Figure l . lb. If the centre conductor couples to a resonant slot cut orthogonally in the upper conductor, the device is said to be a stripline radiator. This phenomenon is used in the dksign of proximity-coupled microstrip patch antenna, which is capable of producing a 13% bandwidth enhancement. This is discussed in chapter 2.

1.2.2 Micrastrip Line

Microstrip line is one of the most popular types of planar transmission lines, primarily because it can be fabricated by photolithographic processes and is easily integrated with other passive and active microwave devices. Microstrip line was a competitor of stripline [2]. The word "Microstrip" is a term which is also commonly applied to non-radiating circuit element such as microwave filters, couplers, tuning stubs and other elements comprising flat conductive strips which are spaced from a single continuous ground plane element by a dielectric layer. It is the most common alternative structure to realise integrated circuits for microwaves, radar and communication purposes. An example of a microstrip line as illustrated in Figure 1.2a, consists of a conductor of width (w) and thickness (t), printed on a substrate of uniform dielectric constant ( ~ r ) . Its height (h) separates it from the ground plane.

A sketch of the electric field and the magnetic field pattern around the transmission line or conductor is shown in Figure 1.2b. The electromagnetic fields are not confined to the dielectric only, but are partly in the air. For this reason, the microstrip line cannot support a pure TEM wave, since the phase velocity of TEM fields in the dielectric region would be

c/& but in the air region is equivalent to that of a free space propagation, c. In

microstrip antenna applications, however, the dielectric substrate is electrically thin, (h<<A), and so the field are essentially the same as those of the static case, i.e. quasi-TEM, where good approximate solution of the phase velocity, propagation constant and characteristic impedance can be obtained [2].

1.2.3 Planar Antenna

Planar antennas may be roughly divided into the following categories [lo];

a. The microstrip antenna - in which a circular or rectangular planar resonator is used as a radiating element,

b. A microstrip line antenna in which the centre conductor of a microstrip line is bent in the form of a crank and used as a radiator,

c. A printed slot antenna in which a slot is set at the ground plane of a microstrip line and used as a radiating element,

d. A printed dipole antenna constructed with the centre conductor and ground plane of a microstrip line, and,

e. A planar radial-line antenna in which a circularly polarised slot or microstrip antenna element is set on the upper surface of a low-loss radial line.

These antennas are shown in Figure 1.3. The research in this thesis was narrowed down to the investigation of the Microstrip patch Antennas performance by studying and analysing its characteristics and parameters that makes the microstrip elements resonates and radiates microwave signals into space. From the list of planar antennas mentioned above, the literature, analysis and experiments in this thesis are done qualitatively, to the characteristics of a linearly polarised square or rectangular microstrip antennas.

1.3 Microstrip Antenna

Microstrip antennas (MSA) [I], also often referred to as patch antennas, comprises a thin, square, rectangular, circular, elliptical, triangular or any other configuration of metal strip or radiating elements that is supported above a conductive ground plane by a dielectric layer. The ground plane, the dielectric substrate and the strips, co-operates to form a small, low cost, compact, low profile and readily mass-producible, high-aperture-efficiency of useful bandwidth resonant antenna [4]. An example of a microstrip antenna is given in Figure 1 .S . These antennas are popular for low-profile applications at frequencies above lOOMHz

(ko<<3m). Practical microstrip antennas have been developed for use from 400MHz to

38GHz, and it can be expected that the technology will soon extend to 60 GHz and beyond 17,141.

Microstrip patch antennas resemble dielectric loaded cavities and they exhibit higher order resonance. By treating this region as a cavity model, the normalised fields within the dielectric substrate can be calculated. This approximated model does not radiate any power. However, this is an accepted approach and similarly, like the perturbation methods which have been successful in the analysis of waveguides, cavities and radiators, the computed pattern, input admittance and resonant frequencies compare well with measurements [ 3 ] .

I . , I

Figure 1.1 (a) A Stripline or Triplate. (b) Electric and Magnetic field lines. Reprinted from [2]

Figure 1.2 (a) Microstrip Line geometry. (b) Electric and Magnetic field lines. Reprinted from [2]

a- 1. Linmly Poladzed M i a o m p Antenna a-2. Circularly Polarized Micmstnp Antenna

b. Microstrip-Line Antenna c. Printed- Slot Antenna

d. Printed-Dipole Ant- e. Radial-Line An

I Figure 1.3 Various type of planar antenna

MICROSTRIP ELEMENT

METAL GROUND PLANE CONNECTOR

Rectangular microstrip-antenna element.

Figure 1.4 An example of a single single rectangular microstrip patch antenna configurations with coaxial-feed connection. Reprinted from [9].

Figure 1.5 A briefcase size S-band microstrip array antenna for Direct Broadcast Satellite Radio (DBSR) service - reprinted from [ 151.

1.4 Advantages and Disadvantages of Microstrip Antenna

Microstrip antennas have been proven to be a significant advance in the established field of antenna technology [5] . Microstrip antennas are available as patch antennas, as travelling wave antennas and as slot antennas, depending upon the geometry chosen for the resonator. A microstrip antenna offers several advantages relative to conventional antennas such as: -

0 Its' size is quite small, having typical dimensions of the order of lOcm x lOcm x lcm. The fabrication costs is low for high volume production. A microstrip antenna has low scattering cross-section. Linear as well as circular (right-hand or left-hand) polarisation for the radiating wave is available. Feed lines are fabricated simultaneously with fabrication of the remainder of the microstrip antenna, and The choice of operating frequency may be chosen over a broad range from 1 OOMHz to 50 GHz.

However, the microstrip antenna atso has certain drawbacks and disadvantages especially on its electrical characteristics such as: -

The operation bandwidth is usually small, with a typical fuH width at half maximum (FWHM) of about 10 MHz. A microstrip antenna has some loss so that gain is limited, usually to 20 dB or less.

,r Except for special designs, a microstrip antenna usually radiates into a half plane and has poor e n d f ~ e performance. Isolation between the feed line and the radiating element is a serious problem

8 It has relatively low power handling capability

As a whole, their versatility in terms of possible geometries makes them applicable for many different situations. Their non-electrical characteristic, and the ease with which an array feed network can be fabricated in microstrip form, also makes them preferred over other types of radiators. The lightweight construction and the suitability for integration with microwave integrated circuits are two more of their numerous advantages. Additionally the simplicity of the structures makes this type of antennas suitable for low-cost manufacturing, and this is also one key-feature why microstrip patch antennas are used in mobile comunications applications.

1.5 Problems, Investigations, Hypothesis and Objectives of Research

1.5.1 Problems

The disadvantages and drawbacks discussed in 1.4 are the main problems associated with microstrip antennas. The electrical performance of the basic single microstrip patch antenna and arrays suffers from a number of serious drawbacks. These includes very narrow bandwidth, high feed network losses, poor cross polarisation and low power handling capacity. On the other hand, analytical and numerical solutions for a wide variety of microstrip patch antennas, often with a high degree of originality and rigor generated by academic and industry researchers is often considered proprietary. With hard works, knowledge, innovative designs and configurations, most of these drawbacks can be avoided, or at least alleviated to some extent

1.5.2 Investigations

The microstrip patch antennas performance was investigated by studying and analysing its characteristics and parameters that makes the microstrip elements resonates and radiates microwave signals into space. The analysis and experiments were done numerically and analytically due to lack of lab facilities and equipment. The report and results of the findings are discussed in chapter 3 and 4.

New ideas and ways in presenting the analysis and design techniques and results of this interesting and most developing topic in the antenna field was one of the target of this thesis. The Computer h d e d Design tools such as the MathCAD version 8.02 and MicroWave Office 2000 (EM structures) version 3.2 simulating software were used to implement these objective.

1.5.3 Objectives

The objectives of this work are as stated below;

i> To study the basic performance and key points in the design of a single patch microstrip antenna, exclusively for a rectangular microstrip patch antenna. This will be followed-up by the design of single rectangular patch microstrip antennas, using the formulas and design charts produced by selected researchers.

ii) To analyse and derive the radiation pattern equation for a rectangular microstrip antenna. This includes computing and plotting the radiation patterns and the 3D- power density patterns of the antenna using MathCAD software.

iii) To analyse the microstrip antenna characteristics such as VSWR at the input,

return loss, magnitude and phase and the radiation characteristics using RFI Microwave Office 2000.

1.5 Methodology

The diagram in Figure 1.6 shows the methodology used and planned in conducting the research.

1.5.1 Literature Review

The literature was done qualitatively, if not quantitatively, for the characteristics of a square or rectangular microstrip patch antennas. To do this, firstly a through study on the Microstrip antenna's characteristics will be carried out. The characteristics of any antennas for any application can be divided into two main categories. These two important and essential characteristics for any application, for all type of antennas are the Radiation Patterns and Input Impedance. Radiation pattern includes Co- and cross-polarised, Axial ratio, Gain, Beamwidth and Sidelobe level whereas Input impedance includes Resonance resistance and Bandwidth. The related topics were looked upon to in the literature to obtain a general knowledge and guidance in conducting the research on this type of antenna.

For the analysis and simulation part of the thesis, previous work done by other researchers were referred to and compared for the validation of (the simulated) work. Reported journal papers entitled "Design of a lOGHz Rectangular Microstrip Patch Antenna Using HP Momentum" written by Heriberto J. Delgado and Michael H. Thursby [S], and "Validation of Predicted HP MDS Momentum Input Impedance Data Using Measured Data for a Rectangular Patch Microstrip Antenna", also written by Heriberto J. Delgado, Sean F. Sullivian and Michael H. Thursby 1251, are specially selected for this purposes. This is due to theirrecent work in the same area and also the fabrication of the antenna mentioned in [25] enables the author to compare his simulation works without fabricating the same antenna. A detailed discussion on their works and results and comparison with the author's work is elaborated in chapter 4.5. Samples of their predicted, measured and statistical results are also shown in this chapter.

1.5.2 Numerical Analysis

The radiation characteristics of microstrip patches placed on planar structures have been studied extensively by scientist [1,4,5]. The far-field radiation pattern of a rectangular microstrip patch operating in the Transverse Magnetic or TM (01) mode (Figure 1.7) is broad in the E and H planes [I]. On the contrary, the step-by-step analysis in producing or plotting the radiation characteristic (numerically) is still not transparent enough for new researchers.

With this in mind, an analysis, which rigorously expands the theoretical steps taken in calculating, computing and plotting the radiation pattern of one particular MSA i.e. the rectangular patch antenna was carried out. Theoretical analysis of the radiation characteristic of a single patch (rectangular) microstrip antenna, referred from selected and distinguished researchers / papers and books [3,4,6,8,10], was carried out and investigated in chapter 3, where a rectangular microstrip antenna was modelled as a four-element slot array. Although approximations were made in the patch model, the steps taken in deriving the radiation pattern equations gave a great deal of the insight on how the antenna works

and radiates its signals into free-space.. An example of a single rectangular microstrip patch antenna configurations with coaxial-feed connection is shown in Figure 1.4. [9].

1.5.3 Simulations through Computer-Aided-Design Software

Microstrip antenna CAD software lags far behind, often committing the designer to costly experimental iterations. Microstrip antenna geometries are relatively difficult to model because of the present of dielectric inhomogeneities and a wide variety of feeding techniques and other geometrical features. This makes the development of a general- purpose microstrip antenna analysis package extremely difficult 1121. On the other hand, CAD tools are very helpful when there are a large numbers of design variables. A study and analysis on the effect of varying a few critical parameters can be carried out with minimum difficulties. Consequently, the author have chosen MathCAD version 8.02 (professional edition) and 'Microwave Office 2000' version 3.2, to compute and analyse microstrip patch antenna in his work.

MathCAD is the industry standard calculation software for technical professionals, educators and college / university students. It is as versatile and powerful as programming languages, yet it's as easy to learn as a spreadsheet. In a programming language, equations were written like; x=(-B+SQRT (B**2-4*A*C))/2*A) etc. and that's assuming we can see them but, usually all we see is a number. In MathCAD, the same equation looks the way we see it on the whiteboard or in a reference book and there is no difficult syntax to learn. It can be used to solve just about any math problems we can think of, symbolically or numerically, especially when dealing with long derivations as is in this research does. Additionally, we can show and illustrate our work with MathCAD's two- and three- dimensional plots.

'Microwave Office 2000' version 3.2 is a completely new suite of RF/microwave design tools built from the ground up for operation in Windows95 and NT environment. EMSIGHTTM full-wave, a three-dimensional electromagnetic (EM) simulator is one of the suites in the software and the entire design solution is constructed using advance object- oriented programming methods that results in impressive performance, reliability and ease of use.

The method of solution for the electromagnetic problem is based on the spectral-domain method applied to three-dimensional circuits in a rectangular enclosure filled with a planar, piece-wise constant stratified media. The rectangular enclosure always has perfectly conducting sides, while the top and bottom of the enclosure can be modelled as perfectly conducting surface, as a lossy surface, or as an infinite waveguide (in the z-directions).

Although it is not necessary that the user understands all the details of EMSight's solution process, a general understanding of the solution process can provide insight that helps them get the best performance from EMSight.

I I

Figure '1.6 Research methodology flow chart

Figure 1.7 Typical principal-plallc lUu.,tion patterns or microsulp parcn antenna (Reprint from [I])

1.6 The Organisation of the Report

This report was organised as follows. The first chapter covers the introduction and the historical background on microstrip antenna technology. The original study of planar antennas, indeed, which utilises stripline as a radiator or feeding system and the transmission-line and microstrip antenna's advantages and disadvantages, which are involved in this research work was discussed briefly. Problems, investigations, objectives and method of research were also highlighted.

In Chapter 2, an evaluation of the basic performance and key points in the design of a single patch microstrip antenna, exclusively for a rectangular microstrip patch antenna was elaborated in detail. This chapter also provides some useful formulas, adopted from distinguished researchers, which was mostly used in the design of microstrip patch antennas and related works. This will be followed-up by the design of single rectangular patch microstrip antennas, using formulas and design charts produced by the selected researchers.

Chapter 3 is the core and point of focus of this research work. It is the most interesting chapter where the analysis and derivation of the radiation pattern equation for a rectangular microstrip antenna over an infinite ground plane is derived in detail. Various principles and theories such as the equivalent principle, slots and cavity model, aperture integration and linear superposition theory are used to produce final radiation equations. The radiation patterns and the 3D-power density patterns of the antenna is computed and plotted using MathCAD version 8.0 software.

Another software, Microwave Office 2000 version 3.2, is also used to analyse the microstrip antenna (from chapter 3) and results such as the VSWR for the input, return loss,

S,, magnitude and phase and the radiation characteristics of the antenna were generated. These are all discussed in Chapter 4. The simulated results are illustrated in the appendices and are compared with that from another research paper done by another researcher using different tool i.e. the HP Momentum. Finally some discussions, conclusion and recommendation is concluded in chapter 5.

CHAPTER 2

MICROSTRIP ANTENNA - AN EVALUATION OF THE BASIC PERFORMANCE AND KEY POINTS IN THE DESIGN OF MICROSTRIP ANTENNAS (MSA)

2.1 Introduction

When antennas are small, bandwidth becomes narrow, radiation efficiency becomes low and their Voltage Standing Wave Ratio (VSWR) becomes very large [lo]. As a result, small antennas, particularly microstrip antennas, having all the required characteristics are very difficult to make. Typically, microstrip antennas are narrow band and their Q factor is inversely proportional to frequency. The main reason for the high Q factor is that microstrip antennas are essentially circuits printed on a relatively thin substrate: the higher the dielectric, the higher the Q factor. Q factor, Bandwidth and efficiency are antennas' figures- of-merit, interrelated and there is no complete freedom to independently optimise each one of them when designing microstrip antenna. However, sometimes there is a desire to optimise one of them, while trading-off the performance of the others and usually, a compromise must be made.

This chapter evaluates and discusses a few important key points in designing a single patch microstrip antenna. In the following topics, the four main elements (Figure 2.1) will be reviewed generally in respect of obtaining the non-electrical and electrical characteristics' requirements of a microstrip antenna.

2.2 Microstrip Antenna

Microstrip antenna is a typical type of planar antenna, first introduced in the mid-1970s by Munson and Howell. However, the original study of planar antennas, which utilises a stripline as a radiator or feeding system, began with the advent of the stripline [4]. Microstrip antenna, in its simplest form (Figure 2. l j consists of a thin electromagnetic resonator layer of carefully chosen dimensions, a dielectric layer contiguous to and separating the resonator and the ground plane, the ground plane, and an antenna signal feed, connected to the resonator at a carefully chosen position. 1.51

From this simple configuration, a vast and comprehensive amount of innovative patented designs [231, analysis method and numerous extensive experiments have merge 131 and are still evolving to meet the ever increasing (applications) demand and requirements for a better performance from this kind of antenna. Discoveries of new materials such as the high frequency circuit materials introduced by Rogers Corporation [Appendix A (i), A (ii) and A (iii)] also provide engineers, researchers and antennas designer with even more design freedom.

Figure 2.1 Perspective view of the basic configuration of microstrip antenna

MICROSTRIP ANTENNA'S POLARITY

1 4

1 LINEAARLY POLARISED

m pEiEEiq I @ Left Hand Polarity Right Hand Polarity

Q

Q 0 8

Figure 2.2 Rectangular and circular microstrip antenna patches shapes according to their respective polarities.

Out of the two distinct characteristics that microstrip antenna has, their non-electrical are more preferred over the electrical characteristic compared to other types of antenna. But, out of all the complex and sophisticated designs (single patches and arrays), they all recall back to the basic performance and key points when one wishes to design one.

The so-called resonator layer or patch element comes in various shapes and this different shape gives various challenging results. Two most favored and practical patches i.e. the rectangular and circular patches are shown in Figurc 3.2. Their shapes can be categorized according to their polarization, i.e. either linearly or circularly polarized and the latter can be subdivided into either single or double feeds systems. Single feed microstrip antennas can be divided again into either Left-Hand Polarity or Right-Hand Polarity and they can be distinguished by their perturbed segments.

A linearly polarized rectangular patch can achieve slightly wider bandwidth than a circular or square patch and on the other hand, a square or circular patch can produce circular polarization by exciting them orthogonally using two feeds 171. Circular patch also excites higher-order modes, which generates different shaped pattern [24]. By inserting perturbed segment, a linearly polarized patch is converted into a circularly polarized antenna. Circularly polarized Microstrip antennas are used as efficient radiators in many communication systems. The effectiveness of the use of these antennas in suppressing unwanted multipath delayed waves has also been demonstrated [24]. An example on how to implcmcnt this pcrturbcd segmcnt is shown in the example in Appendix C (i) and C (ii).