Design and Implementation of Rectangular Patch Antenna for Tri-Band operation

Table of contents

List of Figures

List of Tables

Nomenclature

1 Introduction
1.1 Introduction
1.1.1 Overview of microstrip patch antenna .
1.2 Feed technique
1.2.1 Microstrip feed line
1.2.2 Coaxial feed line
1.2.3 Aperture coupled feed
1.2.4 Proximity couple feed line .

2 Literature survey

3 Problem definition

4 Objective of the book

5 Transmission line model

5.1 Fringing effects
5.2 Effective length, resonant frequency and effective width
5.3 Design
5.3.1 Design procedure
5.4 Conductance
5.5 Resonant input resistance

6 Design patch for tri-band operation
6.1 Antenna geometry I
6.1.1 Mathematical calculations of antenna geometry I
6.2 Antenna geometry - II
6.2.1 Mathematical calculations of antenna geometry II

7 Result and discussion
7.1 Antenna geometry I
7.1.1 Return loss
7.1.2 Voltage standing wave ratio (VSWR)
7.1.3 Current distribution
7.1.4 Radiation pattern
7.2 Antenna geometry II
7.2.1 Return loss
7.2.2 Voltage standing wave ratio (VSWR)
7.2.3 Radiation pattern
7.2.4 Gain
7.2.5 Current distribution

8 Comparison of antenna geometry

9 Conclusion
9.1 Scope for improvement

Bibliography

List of Figures

1.1 Structure of microstrip patch antenna

1.2 Different shapes of MSA

1.3 Microstrip feed line

1.4 Coaxial feed line

1.5 Aperature couple feed line

1.6 Proximity couple feed line

5.1 Microstrip line and its electric field lines, and effective dielectric con- stant geometry

5.2 Effective dielectric constant versus frequency for typical substrates . .

5.3 Top view

5.4 Side view

5.5 Models of rectangular and circular patches

5.6 Rectangular microstrip patch and its equivalent circuit transmission- line model

5.7 Slot conductance as a function of slot width

5.8 Recessed microstrip-line feed

5.9 Normalized input resistance

6.1 Antenna geometry I

6.2 Front view of antenna geometry II

6.3 Back view of antenna geometry II

6.4 Dimesions of patch

7.1 Rectangular patch antenna geometry I

7.2 Return loss of geometry I

7.3 VSWR of geometry I

7.4 Current distribution in the patch and feed line

7.5 E- plane radiation pattern of geometry I

7.6 H- plane radiation pattern of geometry I

7.7 Rectangular patch antenna geometry II

7.8 Return loss of geometry II

7.9 VSWR of geometry II

7.10 E-Plane radiation pattern of geometry II

7.11 H-Plane radiation pattern of geometry II

7.12 Gain of antenna geometry II

7.13 Current distribution in the patch and feed line

List of Tables

1.1 List of few substrate material

1.2 comparison of different feed techniques

8.1 Comparison parameters of geometry I and II

Nomenclature

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About the Authors

Dr. Pramod J Deore was born in 1975. He received a B.E. Degree in Electron- ics 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 Tech- nology, 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 mem- ber 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 Electron- ics 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 Elec- tronics Engineering. He has published 20 papers in National/International Confer- ences/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.

Prashant S Mahajan was born in 1989. He received a B.E. (Electronics and Telecommunication) Degree in 2011 from Godavari College of Engineering, Jalgoan, India and M.E. (Electronics and Telecommunication) Degree in 2013 from R C Patel Institute of Technology, Shirpur, India. He has published 05 papers in National/International Conferences/Journals. His area of interest includes Microstrip antenna design, Microwave filters & Microwave integrated circuits.

Dr. Pramod J Deore, Jagadish B Jadhav, Prashant S Mahajan

Date: April 04, 2015

In today’s modern communication industry, antennas are the most important com- ponents required to create a communication link. Microstrip antennas are the most suited for aerospace and mobile applications because of their low profile, light weight and low power handling capacity. These antennas can be designed in a variety of shapes in order to obtain enhanced gain and bandwidth for dual band and tri-band operation. This book focus on a detailed study of how to design and simulate a microstrip fed rectangular patch antenna using IE3D software with effect of antenna dimensions length (L), width (W), relative dielectric constant (ϵ r), substrate thick- ness (t) on the radiation parameters of bandwidth and gain. The design parameters of the antenna calculated using the transmission line model. Here antenna operates for tri- band operation, the operating bands are GSM , PCA and UTMS for antenna geometry -I and WLAN and WiMAX for antenna geometry -II. The fractional band- widths (FB) after simulation obtain under criterion (S 11 < − 10 dB) are 6 . 45% for GSM [890-960 MHz], 4 . 25% for WLAN [2.40 - 2.51 GHz], 6 . 89% for PCA [1850-1990 MHz], 11 . 42% for WiMAX [3.35 - 3.94 GHz], 9 . 09% for UTMS [1920-2170 MHz] and

18 . 18% for WLAN [5.02 - 6.63 GHz] and peak gain 2.43 dBi at 5.36 GHz.

Keyword: Compact microstrip, Tri-band, GSM, PCA, UTMS, WLAN and WiMAX.

Chapter 1

1.1 Introduction

Antenna is a metallic device (as rod or a wire) for radiating or receiving radio waves. It is a mean of transmitting and receiving radio waves. In another words antenna is transition structure between free space and guided device. The guided device or the transmission line may take the form of the coaxial line or a hollow pipe (waveguide), and is used to transport the electromagnetic energy from the transmitting source to the antenna or from antenna to the receiver. RF and microwave technologies are rapidly finding their way into commercial applications. Industrial applications such as satellite data transfer, vehicle tracking and paging systems have been among the first to be developed. Other applications include mobile telephony, Radio Frequency Identification systems (RFIDs), Direct Broadcast Television (DBS), Wireless Local Area Networks (LANs) and Personal Communications Systems (PCS). The intelli- gent vehicle highway of the future will guide us through traffic jams and systems using Global Positioning System (GPS) will tell us about our location. From being a tech- nology that had its utilization mainly in telecommunications and radar applications, it is today the forefront technology used for wireless applications.

1.1.1 Overview of microstrip patch antenna

The market for wireless applications is expanding and this in turn is constantly driv- ing the demand for a plenty of RF products with increased functionality and inte- gration. As a consequence, recent years have seen rapid changes in RF techniques as well as technology. This trend is continuing enabling the use of increasingly higher RF frequencies with their inherent advantages of smaller component size and larger bandwidth. In particular, the use of planar circuit architecture has opened up new opportunities in terms of reduction in weight, volume, power consumption as well as extension of operating frequencies. Microstrip design is a new era which satis- fies all above requirements. A microstrip antenna consists of conducting patch on a ground plane separated by dielectric substrate. This concept was undeveloped until the revolution in electronic circuit miniaturization and large-scale integration in 1970.

After that many authors have described the radiation from the ground plane by a dielectric substrate for different configurations. The early work of Munson² on microstrip antennas for use as a low profile flush mounted antennas on rockets and missiles showed that this was a practical concept for use in many antenna system problems. Various mathematical models were developed for this antenna and its appli- cations were extended to many other fields. The number of papers, articles published in the journals for the last ten years, on these antennas shows the importance gained by them. These antennas are the present day antenna designer’s choice. Low dielec- tric constant substrate materials are generally preferred for maximum radiation. The conducting patch can take any shape but rectangular and circular configurations are the most commonly used configuration. Other configurations are complex to analyze and require heavy numerical computations. A microstrip antenna is characterized by its length, width, input impedance, and radiation patterns. Microstrip antenna is small in size because the patch’s dimensions are inversely proportional to the square root of the substrate’s dielectric constant ϵ r. The antenna substrate comes in various dielectric constants that can reduce the antenna size. In addition to miniaturization, the patch antenna’s geometry is very simple which makes it easy to model as well as fabricate. A simple patch antenna is composed of a single ground plane at the bottom, a single substrate in the middle, and the top copper patch layer. A simple patch can be designed using a rectangular or circular geometry.

Basic structure

In its most basic form, a microstrip patch antenna consists of a radiating patch on one side of dielectric substrate which has a ground plane on the other side as shown in Figure 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.

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Figure 1.1: Structure of microstrip patch antenna

In order to simplify analysis and performance prediction, the patch is gen- erally square, rectangular, circular, triangular, and elliptical or some other common shape as shown in Figure 1.1. The patch is selected to be very thin such that t ≪ h (where t is the patch thickness). The height h of the dielectric substrate is usually

0 . 003 λ 0 ≤ L ≤ 0 . 05 λ 0 . The dielectric constant of the substrate (ϵ 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. 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 effi- cient and result in narrow bandwidth. Hence a compromise must be reached between antenna dimensions and antenna performance.

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Figure 1.2: Different shapes of MSA

In addition, feeding mechanism can be in term of an edge feed port or it can be implemented using a coaxial or SMA feed probe.

Selection of substrate

The first step in designing an antenna is to select an appropriate substrate. A wide range of substrate materials is available. Low thickness of substrate simplifies the fabrication of the antenna, whereas thicker substrate makes soldering easy. For high power applications of micro strip antennas, a thick substrate is desirable. There is no ideal substrate, the choice rather depends on the application. For instance, confor- mal and wearable microstrip antennas require flexible substrates, while low frequency applications require high dielectric constants to keep size small. Microstrip patch an- tennas use low dielectric substrates. Substrate choice and elevation is an essential part of the design procedure. Many substrate properties may be involved in these consid- erations, dielectric constant and loss tangent and their variation with frequency and temperature, homogeneity, isotropicity, thermal coefficient and temperature range, dimensional stability with processing, humidity, again and thickness uniformity of the substrate are all of importance. Similarly, other physical properties, such as re- sistance to chemicals, tensile and structural strengths, flexibility, impact resistance, strain relief, formability, bond ability and substrate characteristics when clad, are im- portant in fabrication. Substrate dimensions and dielectric constant are functions of substrate temperature, so the operating temperature range must be considered in the result. Applications, where this consideration is important are high-speed missiles, rockets, weaponry, other defense applications. Dielectric constant and loss tangent are also functions of frequency. Thus the properties of the substrates at one frequency cannot be expected to be equally as valid at another frequency. The substrate chosen for design of micro strip antenna in the project is FR4 since it is the most common material used in PCB industry and easily available in market.

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Table 1.1: List of few substrate material

1.2 Feed technique

Microstrip patch antennas can be feed 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. The most popular contacting type feed techniques are.

1. Microstrip line
2. Coaxial probe
3. Aperture coupling
4. Proximity coupling

1.2.1 Microstrip feed line

In this type of feed technique, as shown in figure 1.3, a conducting strip is connected directly to the edge of the microstrip patch. 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 modelling as well as impedance matching.

1.2.2 Coaxial feed line

The coaxial feed or probe feed is a very common technique used for feeding Microstrip patch antennas. As seen from figure 1.4, the inner conductor of the coaxial connector extends through the dielectric and is soldered to the radiating patch, while the outer

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Figure 1.3: Microstrip feed line

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 the ground plane, thus not making it completely planar for thick substrates h ≥ 0 . 002 λ 0.

1.2.3 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 1.5. Coupling between the patch and the feed line is made through a slot or an aperture in the ground plane. The coupling aperture is usually cantered under the patch, leading to lower cross polarization due to symmetry of the configuration. The amount of coupling from the feed line to the

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Figure 1.4: Coaxial feed line

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.

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Figure 1.5: Aperature couple feed line

1.2.4 Proximity couple feed line

This type of feed technique is also called as the electromagnetic coupling scheme. As shown in figure 1.6, 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, 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 below summarizes the characteristics of the different feed techniques.

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Figure 1.6: Proximity couple feed line

Comparison of different feed techniques

In the present work, microstrip line feeding is taken as a preferred method of feeding the input power to the antenna. The calculation of exact patch dimensions of rect- angular microstrip patch antenna becomes ex-tremely important where the antenna size is drastically small. A number of papers have been appeared on the calculation of patch dimension of microstrip antennas. However, these papers suffer considerable deviation in the calculated value of patch dimensions compared to theoretical and simulation findings. calculate the length (L) and width (W) of microstrip patch antenna over a ground plane with a substrate thickness h and dielectric constants r. The results are in good agreement with the simulation findings.

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Table 1.2: comparison of different feed techniques

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