Microstrip Patch Antenna Learning using MATLAB. Theory and Implementation


Scientific Study, 2021

50 Pages


Excerpt

Contents

List of Figures

List of Tables

Nomenclature

1 INTRODUCTION
1.1 Motivation
1.2 ProblemDefination
1.3 Objective of Book
1.4 Organization of the Book

2 LITERATURE REVIEW
2.1 InovationofMicrostripPatchAntenna
2.2 Optimization for High Frequency Use
2.3 Multi frequency Opertion
2.4 MathematicalAnalysisandImplementation

3 THEORY OF MICROSTRIP PATCH ANTENNA
3.1 BasicStructure
3.2 Advantages and Disadvantages
3.3 Feed Techniques
3.3.1 MicrostripLineFeed
3.3.2 Coaxial Feed
3.3.3 Aperture Coupled Feed
3.3.4 ProximityCoupledFeed
3.4 Methods of Analysis
3.4.1 Transmission Line Model
3.4.2 CavityModel
3.4.3 Full Wave Solution - Method of Moments
3.5 Applications
3.5.1 Mobile and satellite communication application
3.5.2 Global Positioning System applications
3.5.3 RadioFrequencyIdentification(RFID)
3.5.4 Worldwide Interoperability for Microwave Access (WiMax)
3.5.5 Radar Application
3.5.6 Rectenna Application
3.5.7 Telemedicine Application
3.5.8 Medicinalapplicationsofpatch

4 IMPLEMENTATION OF GUI FOR MICROSTRIP PATCH ANTENNA
4.1 Antenna Essential Parameters
4.2 GUIofMicrostripPatchAntenna

5 RESULTS & FUTURE SCOPE
5.1 Results
5.2 Future Scope

6 CONCLUSIONS

Bibliography

Publications

Appendix

List of Figures

3.1 Structure of a microstrip patch antenna .

3.2 Common shapes of microstrip patch elements

3.3 Microstriplinefeed

3.4 Probefedrectangularmicrostrippatchantenna

3.5 Aperture-coupled feed

3.6 Proximity-coupledfeed

3.7 (a)Microstripline(b)Electricfieldlines

3.8 Microstrip patch antenna .

3.9 (a)Topviewofantenna(b)Sideviewofantenna

4.1 Front end of GUI for rectangular microstrip patch antenna

4.2 Results for given input in GUI

4.3 HELPmenu

4.4 HELP:Whatismicrostrippatchantenna?

4.5 HELP:Differentmicrostrippatchantenna

List of Tables

3.1 Comparing the different feed techniques

5.1 Comparativeresultsfordifferentdielectricmaterial

Nomenclature

Notations

f r: Resonant frequency

£ r: Relative dielectric constant of substrate.

£ reff: Efective dielectric constant of substrate. h : Substrate thickness

L : Length of patch

L eff: Efective length of patch

AL: Extended length of patch

A0 : Free space wavelength

Q : Quality factor

w : Width of the patch

Acronyms

WLAN : Wireless local area networks

CAD : Computer- aided design

MWO : Microwave office

ADS : Agilent advance design system

hfss : High frequency structure simmulation

GUI : Graphical user interface

min : Minimum

max : Maximum

1G : First generation mobile technology

4G : Fourth generation mobile technology

TV : Television

DTH : Direct to home

MICs : Microwave Integrated Circuits

RF : Radio frequency

TEM : Transverse electromagnetic mode

TMmn : Transverse magnetic mode

GPS : Global positioning system

RFID :Radio frequency identification

WiMax : Worldwide interoperability for microwave access

WBAN : Wireless body area network

GUIDE : Graphical user interface for database exploration

Acknowledgements

Many have contributed to the successful preparation of this text. We would like to place on record our grateful thanks to each one of them.

We wish to express our deep sense of gratitude to many wonderful leaders and educationalists. We acknowledge their influence and express our gratitude to those whose names appear foremost in our mind.

At R. C. Patel Institute of Technology

1. Shri Amrishbhai R. Patel, President, Shirpur Education Society

2. Shri Bupeshbhai R. Patel, Managing Director, Shirpur Education Society

3. Shri R. C. Bhandari, Vice President, Shirpur Education Society

4. Prin. Dr. K. B. Patil, Director, Shirpur Education Society and Former Vice Chancellor NMU, Jalgaon

5. Prin. Dr. J. B. Patil, Principal, R. C. Patel Institute of Technology, Shirpur

At Samarth Collage of Engineering and Technology

1. Shri H. K. Patel, President, Samarth Vividhlaxi Seva Trust, Samarth Campus, Himatnagar

2. Shri Dr. V. R. Patel, Vice President, Samarth Vividhlaxi Seva Trust, Samarth Campus, Himatnagar

3. Prin. Dr. A. C. Suthar, Principal, SCET, Samarth Campus, Himatnagar

4. Prin. D. N. Vandra, Principal, Vedvyas Polytechnic, Samarth Campus, Himatnagar

5. ShriJ.R.Puwar,Campus Director, TATVA Institute of Technological Studies, Modasa

We also express our sincere thanks to our senior colleagues at R. C. Patel Institute of Technology Mr. P. T. Mahajan, Prof. S. P. Shukla, Prof. N. N. Patil, Prof. N. P. Salunke, Prof. S. B. Sharma, Prof. P. R. Bhole, Prof. S. A. More, Prof. S. A. Patil, Prof. V. S. Patil and from Samarth Collage of Engineering and Technology Asst. Prof. M. B. Patel, Asst. Prof. J. B. Suthar, Asst. Prof. S. Kadiya, Asst. Prof. Mrs. D. J. Patel and Asst. Prof. Mrs Sweety V. Patel.

It is with a sense of great joy and pride author Pramod J Deore would like to express his deep sense of gratitude to his parents Tai and Nana, who made several cheerful sacrifices throughout their life to make him what he is today.

He also indebted to his brothers Rajesh, Naresh, sister Manisha and Father in Law Shri B S Patil for their constant encouragement and inspiration for writing this book. Also, he would like to record a high appreciation to his wife Vaishali and daughter Shravani, who gave him tremendous amount of love, understanding and candid support.

Author Alkeshkumar M khatri would like to express his gratitude to his mother Late Ms Kalpana P. Khatri for there continuous blesses with inspiration for him. He also wants to thank his guardians Mr. Yashavant P. Khatri (MAMA) and his Grand Maa Mrs. Girajaben P. Khatri for there continuous care with inspiration. He would like to record a high appreciation to his wife Bhoomika, this journey would not have been possible without her support.

Above all, we praise and thank to God Almighty for having made us successful in our life, for having given us the good times and for having seen us through tough times .

About the Authors

Dr. Pramod J Deore was born in 1975. He received a B.E. Degree in Electronics and Telecom­munication and M.E. degree in Instrumentation Engineering in 1997 and 2000 respectively and subsequently a doctorate degree (Ph.D.) in Electronics and Telecommunication Engineering from SGGS Institute of En­gineering and Technology, Nanded, India, in 2007. He has published 40 papers in National/International Conferences/Journals and he has authored one book. His area of interest includes Robust control, Biometric systems, Microstrip antenna design etc. He is a life member of ISTE. He is at present working as Head of the Department of Electronics and Telecommunication at R C Patel Institute of Technology, Shirpur, India.

Jagadish B Jadhav was born in 1980. He received a B.E. Degree in Electronics Engineering in 2003 and M.Tech. Degree in Electronics and Telecommunication Engineering from Dr. Babasaheb Ambedkar Tech­nological University Lonere, India, in 2007. He is currently pursuing Ph.D under North Maharashtra University in Electronics Engineering. He has published 20 papers in National/International Conferences/Journals. His area of interest includes transceiver front end passive components design, compact planar antennas for wire-less, Digital signal processing etc. He is a life member of ISTE. He is at present working as Associate Professor in Department of Electronics and Telecommunication at R C Patel Institute of Technology, Shirpur, India.

Alkeshkumar M khatri was born in 1985. He received his Diploma (E.C.) in 2005 from N. M. Gopani Polytechnic, Ranpur, Technical Education Board, Gujarat, B.E. (E. & T.C.) Degree in 2008 from R.C.Patel Institute of Technology, Shirpur, Maharashtra, Advanced Diploma (Embedded Software Engineering) in 2008 from Indian Service Machine (I.S.M.), Bangalore, Karnataka and M.E. (E.&T.C.) degree in 2013 from R.C.Patel Institute of Technology, Shirpur, Maharashtra, India. He has published 6 papers in National/International Conferences and Journals.

Presently he is working as Asst. Professor and Head of Electronics & Communication Engineering Depart­ment in Samarth College of Engineering and Technology, Himatnagar under Gujarat Technological University (GTU) and Head of IGNOU- VIEP Study Center at SCET, Himatnagar,Gujarat. His work has primarily focused on Evolution in Teaching Methodology in Engineering Education.

Dr. Pramod J Deore, Jagadish B Jadhav, Alkeshkumar M Khatri.

Date: February 14, 2014

Preface

Satellite communication and wireless communication has been developed rapidly in the past decades and it has already a dramatic impact on human life. In the last few years, the development of wireless local area networks (WLAN) represented one of the principal interests in the information and communication field. Thus, the current trend in commercial and government communication systems has been to develop low cost, minimal weight, low profile antennas that are capable of maintaining high performance over a large spectrum of frequencies. This technological trend has focused much effort into the design of microstrip (patch) antennas.

The variety in design that is possible with microstrip antenna probably exceeds that of any other type of antenna element. In addition, once the shape and operating mode of the patch are selected, designs become very versatile in terms of operating frequency, polarization, pattern, and impedance. They are extremely low profile, lightweight, simple and inexpensive to fabricate using modern day printed circuit board technology, compatible with microwave and millimeter-wave integrated circuits (MMIC), and have the ability to conform to planar and non planar surfaces.

Understanding the behaviour of the microstrip patch antenna and design of it for different application with the use of the graphical user interface using MATLAB is better way of analysis.

In this book, we have focused on different peramets for the designing the Microstrip Patch Antenna with different input condition like changes in Antenna Design Material and etc.

A text book is not a original work by its nature but give idea of a other vision of seeing the same things from us. The text has been drawn from the available published literature on the subject.

Keywords: Rectangular microstrip patch antenna, circular misrostrip patch antenna, Graphical User Interface (GUI), MATLAB.

Chapter 1

INTRODUCTION

1.1 Motivation

Satellite communication and wireless communication has been developed rapidly in the past decades and it has already a dramatic impact on human life. In the last few years, the development of wireless local area networks (WLAN) represented one of the principle interests in the information and communication field. Thus, the current trend in commercial and government communication systems has been to develop low cost, minimal weight, low profile antennas that are capable of maintaining high performance over a large spectrum of frequencies. This technological trend has focused much effort into the design of microstrip (patch) antennas. Due to advantages and applications of microstrip patch antenna it is necessary to study it from basic level to application level.

Studying antennas and wave propagation phenomena using interactive graphics and animations becomes nowadays a fundamental tool for describing and understanding electromagnetic concepts 4. This aspect is strongly related with wave propagation, where the propagation properties of the waves or how to plot the radiation patterns of antennas are not so easy to understand for undergraduate students, due to simple, static, oral explanations.

Computer modelling techniques that allow an accurate simulation of the behaviour of real devices have become increasingly more common and popular with the availability of cheaper and ever more powerful computer resources. The majority of microwave engineers today design the planar components and integrated circuits without direct recourse to electromagnetic analysis. Microwave computer-aided design (CAD) software is the essential tool of today's microwave engineer. Currently, several products in which computer tools are used have been developed such as Ansoft Ensemble, IE3D, MWO (Microwave Office), SONNET, ADS (Agilent Advance Design System), COMSOL, MATLAB, HFSS (High Frequency Structure Simulation) etc for modelling and simulation of complicated microwave and RF printed circuit, antennas and other electronics component . Many of these softwares are commercially available at a very high cost or in the least, are proprietary 1.

MATLAB has become a ubiquitous math, data manipulation, signal processing, and graphics software package 1. Engineers use its powerful functions for analysis and design in many areas including antenna design. MATLAB is general-purpose software, so many arcane applications, like antenna design, are done using special purpose commercial software. Although these packages can model very complex electromagnetic systems, they lack some of the powerful analysis tools in MATLAB. Using MATLAB to control these commercial electromagnetic solvers creates a powerful tool for design, analysis, and control. This is achieved via GUI generated by the MATLAB that allow the user to modify, visualize and compare the whole process of the design whenever there is a need to fabricate the antenna.

1.2 Problem Defination

As mention above satellite communication and wireless communication has been developed rapidly in the past decades and it has already a dramatic impact on human life. In the last few years, the development of wireless local area networks (WLAN) represented one of the principal interests in the information and communication field. Due to advantages and applications of microstrip patch antenna, it is necessary to study it from basic level to application level. Microwave computer-aided design (CAD) software is the essential tool of todays microwave engineer. It is difficult to nd and derive an analytical formulation of different antennas for different frequency applications. The analytical solutions are suitable for CAD software packages, which are quite expensive. They are also difficult and take a long time to create a program because of the complicated mathematical routines . Preparation of the CAD design for the microstrip patch antenna is become the basic needs of our designing.

1.3 Objective of Book

Microstrip patch antenna is used to send onboard parameters of article to the ground while under oper­ating conditions. By the study of this book we find, how to investigate a new method of teaching microstrip patch antenna design for undergraduate students by using MATLAB. This is achieved by designing a friendly graphical user interface (GUI) for microstrip patch antennas through which antenna parameters and radiation pattern can be determined. Effect of changes in basic parameter microstrip patch antenna on its radiation pat­tern and other parameters i.e. calculate parameters of rectangular microstrip patch antenna to study the effect of resonant frequency (f r) and substrate parameters like, relative dielectric constant (E r), substrate thickness (h) on the radiation parameters of bandwidth and physical dimension of the microstrip patch antenna can be determined by using GUI.

In this book we develops simple CAD (GUI) formulas that describe the basic properties of microstrip patch antenna using MATLAB. By the usage of this teaching tool we can analyze the behaviour of the microstrip patch antenna and design of it for different material.

1.4 Organization of the Book

Chapter 1 includes an introduction of this book. Chapter 2 deals with the literature review of the microstrip patch antenna and its evaluation. Chapter 3 deals with the microstrip patch antenna structures, advantages and disadvantages, the various feeding techniques and models of analysis were listed with applications of the microstrip patch antenna.

Chapter 4 provides the design and development of GUI using MATLAB for microstrip patch antenna i.e. implementation work of this work are mention here. Chapter 5 provides comparative results for the different dielectric materials. Chapter 6 gives the conclusion to this book and future prospects.

Chapter 2

LITERATURE REVIEW

2.1 Inovation of Microstrip Patch Antenna

The invention of microstrip patch antennas has been attributed to several authors, but it was certainly dates in the 1960's with the first works published by Deschamps, Greig and Engleman, and Lewin, among others. After the 1970's research publications started to flow with the appearance of the first design equations. Since then different authors started investigations on microstrip patch antennas like James Hall and David M. Pozar and there are also some who contributed a lot 14. Throughout the years, authors have dedicated their investigations to creating new designs or variations to the original antenna that, to some extent produce either wider bandwidths or multiple-frequency operation in a single element. However, most of these innovations bear disadvantages related to the size, height or overall volume of the single element and the improvement in bandwidth suffers usually from a degradation of the other characteristics.

2.2 Optimization for High Frequency Use

With bandwidths as low as a few percent, broadband applications using conventional microstrip patch designs are limited. Other drawbacks of patch antennas include low efficiency, limited power capacity, spurious feed radiation, poor polarization purity, narrow bandwidth, and manufacturing tolerance problems [5,6,12,25]. For over two decades, research scientists have developed several methods to increase the bandwidth and low frequency ratio of a patch antenna. Many of these techniques involve adjusting the placement and/or type of element used to feed (or excite) the antenna. Over the last two decades the wireless communication system has experienced a significant growth from first generation (1G) analog voice signal to forthcoming fourth generation (4G) mobile technology. The motto of 4G communication system is to provide Wi-Fi communication network and high quality audio and video services 3.

In 2010-11, research was taken out on the microstrip patch antenna for the application of it for the higher frequency band like Ku band for the TV broadcasting and reception by using DTH system and more [10, 11, 15].

2.3 Multi frequency Opertion

As the revolution in the communication systems, higher data rate with high speed are needed. As a part of it from 1989 - 1993, development of patch antenna was going on [17, 18]. In 2009 - 2010, the patch antenna are properly configured for the Multi frequency by Murli Manohar, S. K. Behera, P. K. Sahu & Dr. T. K. Bandoupadhya, Dr. Anubhuti Khare, Rajesh Nema, Puran Gour [2,6].

2.4 Mathematical Analysis and Implementation

Importance of the microstrip patch antenna are increasing day by day due to its advantages of low profile, light weight and ability of high frequency operation study of it become essential. By the use of different computer tools like IE3D, PSO, MATLAB etc done. In all available computer tools, use of MATLAB become easy by preparing the Graphical user interface for different patch antennas, which was developed during 2010-2012 [8, 13, 16, 19, 27].

Chapter 3

THEORY OF MICROSTRIP PATCH ANTENNA

3.1 Basic Structure

In its most basic form, a microstrip patch antenna consists of a radiating patch on one side of a dielectric substrate which has a ground plane on the other side as shown in figure 3.1 1. The patch is generally made of conducting material such as copper or gold and can take any possible shape. The radiating patch and the feed lines are usually photo etched on the dielectric substrate.

In order to simplify analysis and performance prediction, the patch is generally square, rectangular, circular, triangular, elliptical or some other common shape as shown in figure 3.2. For a rectangular patch, the length L of the patch is usually 0.3333A0 < L < 0.5A0 ,whereA0 is the free-space wavelength. The patch is selected to be very thin such that t ^A0 (where t is the patch thickness). The height h of the dielectric substrate is usually 0.003AO < h < 0.05A0. The dielectric constant of the substrate (E r) is typically in the range

2.2 <Er < 12.

Microstrip patch antennas radiate primarily because of the fringing fields between the patch edge and the ground plane. For good antenna performance, a thick dielectric substrate having a low dielectric constant is desirable since this provides better efficiency, larger bandwidth and better radiation 5. However, such a configuration leads to a larger antenna size. In order to design a compact microstrip patch antenna, higher dielectric constants must be used which are less efficient and result in narrower bandwidth. Hence a compromise must be reached between antenna dimensions and antenna performance.

3.2 Advantages and Disadvantages

Microstrip patch antennas are increasing in popularity for use in wireless applications due to their low- profile structure. Therefore they are extremely compatible for embedded antennas in hand held wireless devices such as cellular phones, pagers etc. The telemetry and communication antennas on missiles need to be thin and conformal and are often microstrip patch antennas. Another area where they have been used successfully is in satellite communication. Some of their principal advantages discussed by T. D. Prasad 16 are given below:

- Light weight and low volume.

Abbildung in dieser Leseprobe nicht enthalten

Figure 3.1: Structure of a microstrip patch antenna

- Low profile planar configuration which can be easily made conformal to host surface.
- Low fabrication cost, hence can be manufactured in large quantities.
- Supports both, linear as well as circular polarization.
- Can be easily integrated with microwave integrated circuits (MICs).
- Capable of dual and triple frequency operations.
- Mechanically robust when mounted on rigid surfaces.

Microstrip patch antennas suffer from a number of disadvantages as compared to conventional antennas. Some of their major disadvantages discussed by T. D. Prasad 17 are given below:

- Narrow bandwidth.
- Low efficiency.
- Low gain.
- Extraneous radiation from feeds and junctions.
- Poor end fire radiator except tapered slot antennas.
- Low power handling capacity.
- Surface wave excitation.

Microstrip patch antennas have a very high antenna quality factor (Q). Q represents the losses associated with the antenna and a large Q leads to narrow bandwidth and low efficiency. Q can be reduced by increasing the thickness of the dielectric substrate. But as the thickness increases, an increasing fraction of the total power delivered by the source goes into a surface wave. This surface wave contribution can be counted as an unwanted power loss since it is ultimately scattered at the dielectric bends and causes degradation of the

Abbildung in dieser Leseprobe nicht enthalten

Triangular Circular Ring Elliptical

Figure 3.2: Common shapes of microstrip patch elements

antenna characteristics. However, surface waves can be minimized by use of photonic bandgap structures as discussed by Quan Hui Sun 11. Other problems such as lower gain and lower power handling capacity can be overcome by using an array configuration for the elements.

3.3 Feed Techniques

Microstrip patch antennas can be fed by a variety of methods. These methods can be classified into two categories - contacting and non - contacting. In the contacting method, the RF power is fed directly to the radiating patch using a connecting element such as a microstrip line. In the non-contacting scheme, electromagnetic field coupling is done to transfer power between the microstrip line and the radiating patch 1. The four most popular feed techniques used are the microstrip line, coaxial probe (both contacting schemes), aperture coupling and proximity coupling (both non-contacting schemes).

3.3.1 Microstrip Line Feed

In this type of feed technique, a conducting strip is connected directly to the edge of the microstrip patch as shown in figure 3.3. The conducting strip is smaller in width as compared to the patch and this kind of feed arrangement has the advantage that the feed can be etched on the same substrate to provide a planar structure.

The purpose of the inset cut in the patch is to match the impedance of the feed line to the patch without the need for any additional matching element. This is achieved by properly controlling the inset position. Hence this is an easy feeding scheme, since it provides ease of fabrication and simplicity in modeling as well as impedance matching. However as the thickness of the dielectric substrate being used, increases, surface waves and spurious feed radiation also increases, which hampers the bandwidth of the antenna 1. The feed radiation also leads to undesired cross polarized radiation.

Abbildung in dieser Leseprobe nicht enthalten

Abbildung in dieser Leseprobe nicht enthalten

Substrate

Abbildung in dieser Leseprobe nicht enthalten

Connector

Figure 3.4: Probe fed rectangular microstrip patch antenna

3.3.2 Coaxial Feed

The coaxial feed or probe feed is a very common technique used for feeding microstrip patch antennas. As seen from Figure 3.4, the inner conductor of the coaxial connector extends through the dielectric and is soldered to the radiating patch, while the outer conductor is connected to the ground plane.

The main advantage of this type of feeding scheme is that the feed can be placed at any desired location inside the patch in order to match with its input impedance. This feed method is easy to fabricate and has low spurious radiation. However, its major disadvantage is that it provides narrow bandwidth and is difficult to model since a hole has to be drilled in the substrate and the connector protrudes outside the ground plane, thus not making it completely planar for thick substrates ( h > 0.02A0 ). Also, for thicker substrates, the increased probe length makes the input impedance more inductive, leading to matching problems 9. It is seen above that for a thick dielectric substrate, which provides broad bandwidth, the microstrip line feed and the coaxial feed suffer from numerous disadvantages. The non-contacting feed techniques which have been discussed below, solve these problems.

3.3.3 Aperture Coupled Feed

In this type of feed technique, the radiating patch and the microstrip feed line are separated by the ground plane as shown in figure 3.5. Coupling between the patch and the feed line is made through a slot or an aperture in the ground plane.

Abbildung in dieser Leseprobe nicht enthalten

The coupling aperture is usually centered under the patch, leading to lower cross polarization due to symmetry of the configuration. The amount of coupling from the feed line to the patch is determined by the shape, size and location of the aperture. Since the ground plane separates the patch and the feed line, spurious radiation is minimized. Generally, a high dielectric material is used for the bottom substrate and a thick, low dielectric constant material is used for the top substrate to optimize radiation from the patch 5. The major disadvantage of this feed technique is that it is difficult to fabricate due to multiple layers, which also increases the antenna thickness. This feeding scheme also provides narrow bandwidth.

3.3.4 Proximity Coupled Feed

This type of feed technique is also called as the electromagnetic coupling scheme. As shown in figure 3.6, two dielectric substrates are used such that the feed line is between the two substrates and the radiating patch is on top of the upper substrate. The main advantage of this feed technique is that it eliminates spurious feed radiation and provides very high bandwidth (as high as 13%) 5, due to overall increase in the thickness of the microstrip patch antenna. This scheme also provides choices between two different dielectric media, one for the patch and one for the feed line to optimize the individual performances. Matching can be achieved by controlling the length of the feed line and the width-to-line ratio of the patch. The major disadvantage of this feed scheme is that it is difficult to fabricate because of the two dielectric layers which need proper alignment. Also, there is an increase in the overall thickness of the antenna.

Table 3.1 below summarizes the characteristics of the different feed techniques.

Abbildung in dieser Leseprobe nicht enthalten

Figure 3.6: Proximity-coupled feed

Table 3.1: Comparing the different feed techniques 4

Abbildung in dieser Leseprobe nicht enthalten

3.4 Methods of Analysis

The most popular models for the analysis of microstrip patch antennas are the transmission line model, cavity model, and full wave model (which include primarily integral equations/Moment Method). The trans­mission line model is the simplest of all and it gives good physical insight but it is less accurate. The cavity model is more accurate and gives good physical insight but is complex in nature. The full wave models are extremely accurate, versatile and can treat single elements, finite and infinite arrays, stacked elements, arbitrary shaped elements and coupling. It must be noted that book is centered on the transmission line model and uses all of the empirical equations of this model is based on for preparation of GUI. The cavity model and method of moments are not at the centre of our book and is hence not explained very briefly.

3.4.1 Transmission Line Model

This model represents the microstrip antenna by two slots of width W and height h, separated by a transmission line of length L. The microstrip is essentially a non homogeneous line of two dielectrics, typically the substrate and air. figure 3.7(a) illustrates this.

Abbildung in dieser Leseprobe nicht enthalten

Figure 3.7: (a) Microstrip line (b) Electric field lines

Hence, as shown in figure.3.7 (b), most of the electric field lines lies in the substrate and parts of some lines are in air. As a result, this transmission line do not support pure transverse - electromagnetic mode of transmission, since the phase velocities would be different in the air and the substrate. Instead, the dominant mode of propagation would be the quasi- TEM mode. Hence, an effective dielectric constant (£ re ff) must be obtained in order to account for the fringing and the wave propagation in the line. The value of £ re ff is little less then £r because the fringing fields around the edge of the patch are not confined in the dielectric substrate but are also spread in the air as shown in figure above. The expression for £ref f can be given as:

Abbildung in dieser Leseprobe nicht enthalten

Figure 3.8: Microstrip patch antenna

Consider figure 3.8, which shows a rectangular microstrip patch antenna of length L, width W lying on a substrate of height h. The co-ordinate axis is selected in such a way that the length is along the x axis direction, width is along the y axis direction and the height is along the z axis direction.

It is shown in figure 3.9. b that the normal components of the electric field at the two edges along

Abbildung in dieser Leseprobe nicht enthalten

Figure 3.9: (a) Top view of antenna (b) Side view of antenna

the width are in opposite directions and thus out of phase since the patch is A /2 long and hence they nullify each other 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. Hence the edges along the width can be represented as two radiating slots, which are A /2 apart and excited in phase and radiating in the half space above the ground plane. The fringing fields along the width can be modeled as radiating slots

and electrically the patch of the microstrip antenna looks greater than its physical dimensions. The dimensions of the patch along its length have now been extended on each end by a distance AL, which is given empirically

Abbildung in dieser Leseprobe nicht enthalten

3.4.2 Cavity Model

Although the transmission line model discussed in the previous section is easy to use, it has some inherent disadvantages. Specifically, it is useful for patches of rectangular design and it ignores field variations along the radiating edges. These disadvantages can be overcome by using the cavity model. In this model, the interior region of the dielectric substrate is modeled as a cavity bounded by electric walls on the top and bottom. The basis for this assumption is the following observations for thin substrates (h^ A).

1. Since the substrate is thin, the fields in the interior region do not vary much in the z direction, i.e. normal to the patch.
2. The electric field is z directed only, and the magnetic field has only the transverse components Hx and Hy in the region bounded by the patch metallization and the ground plane. This observation provides for the electric walls at the top and the bottom.

[...]

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Details

Title
Microstrip Patch Antenna Learning using MATLAB. Theory and Implementation
Course
M. Tech
Authors
Year
2021
Pages
50
Catalog Number
V1037777
ISBN (eBook)
9783346453655
ISBN (Book)
9783346453662
Language
English
Tags
microstrip, patch, antenna, learning, matlab, theory, implementation
Quote paper
Jagadish Jadhav (Author)Alkeshkumar M Khatri (Author)Dr. Pramod J Deore (Author), 2021, Microstrip Patch Antenna Learning using MATLAB. Theory and Implementation, Munich, GRIN Verlag, https://www.grin.com/document/1037777

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