INVESTIGATE AND OPTIMIZE THE VIVALDI ANTENNA FOR ULTRA-WIDEBAND APPLICATIONS

LIM CHIA ROENG

This Report Is Submitted In Partial Fulfilment of Requirements for the BachelorDegree of Electronic Engineering (Wireless Communication)

Faculty of Electronic and Computer Engineering

Universiti Teknikal Malaysia Melaka

JUNE 2016

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UNIVERSTI TEKNIKAL MALAYSIA MELAKA FAKULTI KEJURUTERAAN ELEKTRONIK DAN KEJURUTERAAN KOMPUTER

BORANG PENGESAHAN STATUS LAPORAN

PROJEK SARJANA MUDA II

Tajuk Projek : INVESTIGATE AND OPTIMIZE VIVALDI ANTENNA

FOR ULTRA-WIDEBAND APPLICATION

Sesi Pengajian :

1 5 / 1 6

Saya …………LIM CHIA ROENG……………………………………………………………………….. mengaku membenarkan Laporan Projek Sarjana Muda ini disimpan di Perpustakaan dengan syarat-syarat kegunaan seperti berikut:

1. Laporan adalah hakmilik Universiti Teknikal Malaysia Melaka.

2. Perpustakaan dibenarkan membuat salinan untuk tujuan pengajian sahaja.

3. Perpustakaan dibenarkan membuat salinan laporan ini sebagai bahan pertukaran antara institusi

pengajian tinggi.

4. Sila tandakan ( √ ) :

SULIT*

*(Mengandungi maklumat yang berdarjah keselamatan atau

kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972)

TERHAD**

**(Mengandungi maklumat terhad yang telah ditentukan oleh

organisasi/badan di mana penyelidikan dijalankan)

TIDAK TERHAD

Disahkan oleh:

________________________ ___________________________________ (TANDATANGAN PENULIS) (COP DAN TANDATANGAN PENYELIA)

Tarikh: ……………………….. Tarikh: ………………………..

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“I hereby declare that the work in this project is my own except for summaries and quotations which have been duly acknowledge.”

Signature : ....................................................... Author : LIM CHIA ROENG Date : .......................................................

iv

“I acknowledge that I have read this report and in my opinion this report is sufficient in term of scope and quality for the award of Bachelor of Electronic Engineering

(Wireless Communication) with Honours.”

Signature : ....................................................... Supervisor’s Name : MADAM NORBAYAH BINTI YUSOP Date : .......................................................

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To my beloved friends and family. Thank you my supervisor and all lecturers who guide me,

and to all my friends for giving me mentally and moral support during process of finish final

year project.

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ACKNOWLEDGEMENT

I would like to express my deepest appreciation to all those who provided me the

possibility to complete this report. A special gratitude I give to my supervisor, Madam

Norbayah Binti Yusop and co-supervisor, Dr. Mohd Azlishah Bin Othman who had given me

many learning opportunities throughout the preparation of this report. Besides giving me

suggestions, they had also helped me to coordinate my project, especially in writing this report.

I am highly indebted to Madame Norbayah for her guidance and constant supervision as well

as for accessing my progress and also for her support in completing this report.

Furthermore, I would also like to acknowledge with much appreciation of my friends

for providing decent suggestions and necessary information during the completion of this

report.

I have taken efforts in this project. However, it would not have been possible without

the kind support and help of many individuals. I would like to extend my sincere thanks to all

of them. Last but not least, I would like to thank my parents and family for their support

financially and emotionally.

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ABSTRACT

An exponentially tapered slot line antenna named the Vivaldi is studied in this thesis.

This antenna has Ultra-Wideband (UWB) characteristics and is used in applications ranging

from feeds reflectors to microwave imaging. In this project, a Vivaldi antenna with different

dimensions of feedline and substrate are designed and presented. The optimization of Vivaldi

antenna used to improve the basic antenna parameters. Besides that, the Antipodal Vivaldi

antenna is studied and modified in order to improve the return loss and gain of the antenna.

The Computer Simulation Technology (CST) software is used in design the antenna. The

proposed antenna will cover the frequency range from 3.1 GHz to 10.6 GHz. The

characteristics of UWB antenna will be proved from the radiation pattern of the proposed

antenna.

Keywords: Ultra-Wideband, Antipodal Vivaldi Antenna, return loss, gain

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ABSTRAK

Dalam tesis ini, antena jenis garis slot tirus yang bernama Vivaldi telah diperkenalkan.

Antenna tersebut mempunyai ciri-ciri Ultra Wideband (UWB) dan digunakan dalam aplikasi

antara julat frekuensi UWB contohnya dalam pengimejan microwave. Pelbagai jenis dimensi

dari segi feedline dan substrat untuk antena Vivaldi telah direka dan dibentangkan dalam tesis

tersebut. Antena Vivaldi yang telah beroptimum tersebut untuk meningkat asas parameter

antena dari segi return loss dan gain. Selain itu, perisian Computer Simulation Technology

(CST) telah digunakan dalam mereka antenna tersebut. Antena yang telah dicadangkan

meliputi julat frekuensi dari 3.1 GHz ke 10.6 GHz. Ciri-ciri antena UWB telah dibukti dari segi

corak radiasi bagi antena tersebut.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

PROJECT TITLE i

REPORT STATUS APPROVAL FORM ii

DECLARATION iii

SUPERVISOR APPROVAL iv

DEDICATION v

ACKNOWLEDGEMENT vi

ABSTRACT vii

ABSTRAK viii

TABLE OF CONTENT ix

LIST OF FIGURES xii

LIST OF TABLES xv

LIST OF ABBREVIATION xvi

I INTRODUCTION

1.1 INTRODUCTION 1

1.2 BACKGROUND 1

1.3 PROBLEM STATEMENT 4

1.4 SIGNIFICANCE OF STUDY 5

1.5 OBJECTIVES OF STUDY 5

1.6 SCOPE OF PROJECT 6

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1.7 THESIS OUTLINE 6

II LITERATURE REVIEW

2.1 INTRODUCTION 8

2.2 BASIC ANTENNA PARAMETER 8

2.2.1 RADIATION PATTERN 9

2.2.2 BANDWIDTH 11

2.2.3 DIRECTIVITY AND GAIN 12

2.3 TAPERED SLOT ANTENNA (TSA) 12

2.3.1 TAPER PROFILE 12

2.3.2 SUBSTRATE MATERIAL 13

2.4 BASIC GEOMETRY OF VIVALDI ANTENNA 14

2.5 MICROSTRIP/ STRIPLINE TO SLOTLINE TRANSITIONS 15

2.6 ANTIPODAL VIVALDI ANTENNA 16

2.7 BALANCED ANTIPODAL VIVALDI ANTENNA 17

2.8 EVALUATION NOTES

2.8.1 TAPERED SLOT VIVALDI ANTENNA

2.8.8.1 INFLUENCE OF THE EXPONENTIAL

CURVATURE

2.8.1.2 USING SPLINE CURVES FOR TAPER

DEFINITION

2.8.1.3 INFLUENCE OF THE ANTENNA

DIMENSIONS

2.8.1.4 INFLUENCE OF THE ROUND CORNERS

2.8.1.5 COMB STRUCTURE

2.8.1.6 HYBRID EXPONENTIAL MODEL

2.8.2 ANTIPODAL VIVALDI ANTENNA

2.8.2.1 INFLUENCE OF THE INNER

CURVATURE PROFILE

2.8.2.2 USING SPLINE CURVES FOR INNER

19

19

20

22

22

24

25

27

27

28

29

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PROFILE

2.8.2.3 INFLUENCE OF THE OUTER

CURVATURE PROFILE

2.8.2.4 INFLUENCE OF THE FIN WIDTH

2.8.2.5 INFLUENCE OF THE CORNERS

29

30

31

III RESEARCH METHODOLOGY

3.1 INTRODUCTION 33

3.2 METHOD 33

3.3 SIMULATION 35

3.3.1 CST 2014 MICROWAVE STUDIO SUITE 35

3.4 PRELIMINARY PREPARATION 35

3.5 DESIGN PARAMETER AND LAYOUT 36

IV RESULTS AND DISCUSSIONS

4.1 INTRODUCTION 37

4.2 WIDTH OF FEEDLINE 38

4.3 WIDTH OF SUBSTRATE 43

4.4 LENGTH OF SUBSTRATE 48

V CONCLUSION AND RECOMMENDATION

5.1 CONCLUSION 53

5.2 FUTURE WORK 54

REFERENCES 56

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LIST OF FIGURES

NO TITLE PAGE 1.1 Difference between compressed signals in time domain to the one

expanded in time domain 2

1.2 FCC spectral masks for outdoor unlicensed UWB emission 3 2.1 Three dimensional coordinate system 10 2.2 Radiation Pattern 10 2.3 Three basic taper profiles 13 2.4 Basic geometry shape of the Vivaldi Antenna 14 2.5 Microstrip line to slotline transition 15 2.6 Microstrip to slotline transition with radial stub 16 2.7 Structure of Antipodal Vivaldi Antenna 17 2.8 Cross sectional view of the top of the antipodal Vivaldi and the

skew in electric field across the slot of the antenna 18

2.9 Balanced Antipodal Vivaldi Antenna 18 2.10 Cross sectional view of the top of the balanced antipodal Vivaldi

depicting the resultant E-field across the slot of the antenna 19

2.11 Schema of the tapered slot Vivaldi antenna design and variables 20 2.12 Taper profiles and signals reflected from the structure for various

settings of parameter p 21

2.13 Return loss and fidelity factor F for various settings of parameter p 21 2.14 Return loss and reflected signal for various settings of aperture

width aw 23

2.15 Round Corner design and reflected signal for various settings of corner radius R

24

2.16 Return loss and signal level received at the back probe for various settings of corner radius R

25

2.17 Two investigated comb structures – capacitive comb and resistive comb

26

2.18 Return loss and signal level received at the front probe for both comb structures

26

2.19 Hybrid taper design, description of antipodal design and its variables

27

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2.20 Inner curvature profiles and signals reflected from the structure for various settings of parameter p1.

28

2.21 Return loss and fidelity factor F for various settings of parameter p1.

29

2.22 Outer curvature profiles and signals reflected from the structure for various settings of parameter p2

30

2.23 Return loss and signals reflected from the structure for various settings of parameter L2

31

2.24 Antipodal round corner design and reflected signal for various settings of corner radius R

31

2.25 Return loss and fidelity factor F for various settings of corner radius R

32

3.1 Flow chart of design process 34 3.2 Basic Structure and parameters of Antipodal Vivaldi Antenna 36 4.1 Return Loss with varied width (a) 3.2 mm, (b) 4.2 mm and (c) 5.2

mm 38

4.2 VSWR with varied width (a) 3.2 mm, (b) 4.2 mm and (c) 5.2 mm 39 4.3 Gain with feedline width 3.2 mm 41 4.4 Gain with feedline width 4.2 mm 41 4.5 Gain with feedline width 5.2 mm 42 4.6 Return Loss with varied width (a) 100 mm, (b) 90 mm and (c) 80

mm 43

4.7 VSWR with varied width (a) 100 mm, (b) 90 mm and (c) 80 mm 44 4.8 Gain with substrate width 100 mm 46 4.9 Gain with substrate width 90 mm 46 4.10 Gain with substrate width 80 mm 47 4.11 Return Loss with varied length (a) 95 mm, (b) 90 mm and (c) 80

mm 48

4.12 VSWR with varied length (a) 95 mm, (b) 90 mm and (c) 80 mm 49 4.13 Gain with Substrate Length 95 mm 51 4.14 Gain with Substrate Length 90 mm 51 4.15 Gain with Substrate Length 85 mm 51

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LIST OF TABLE

NO TITLE PAGE 3.1 The dimension of Proposed Antenna 36 4.1 Return Loss with varied width (a) 3.2 mm, (b) 4.2 mm and (c) 5.2

mm 39

4.2 VSWR with varied width (a) 3.2 mm, (b) 4.2 mm and (c) 5.2 mm 40 4.3 Gain of antenna with varied width (a) 3.2 mm, (b) 4.2 mm and (c)

5.2 mm 42

4.4 Return Loss with varied width (a) 100 mm, (b) 90 mm and (c) 80 mm

44

4.5 VSWR with varied width (a) 100 mm, (b) 90 mm and (c) 80 mm 45 4.6 Gains with varied width (a) 100 mm, (b) 90 mm and (c) 80 mm 47 4.7 Return Loss with varied length (a) 95 mm, (b) 90 mm and (c) 80

mm 48

4.8 VSWR with varied length (a) 95 mm, (b) 90 mm and (c) 80 mm 50 4.9 Gain with varied length (a) 95 mm, (b) 90 mm and (c) 80 mm 52

xv  

LIST OF ABBREVIATION

UWB - Ultra-Wideband

FCC - Federal Communications Commission

PSD - Power Spectral Density

CST - Computer Simulation Technology

HPBW - Half Power Beamwidth

VSWR - Voltage Standing Wave Ratio

TSA - Tapered Slot Antenna

BAVA - Balanced Antipodal Vivaldi Antenna

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CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION

In this chapter, Vivaldi antenna for Ultra Wideband (UWB) application will be

discussed. The Ultra Wideband technology also will be briefly explained. A summary

and the aim of this project will also be presented and discussed in this section.

1.2 BACKGROUND

Nowadays, the speed of expanding technology in this generation become faster

compare to pass decade. The limitation of frequency spectrum become the factors in

expanding of technology due to the innovation of new applications. The Ultra Wide

Band is introduced to overcome this problems. UWB is a technology which transfer

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the data at low spreading of radio energy. The transmission of data has very low power

spectral densities over the wide band frequencies. This low power spectral densities is

useful in the limitation of interference between the radio systems. Due to the higher or

wider bandwidth, a very high data throughput is allowed for the communication

devices with high precision for location or imaging devices [1]. Ultra Wideband radio

transmission is a revolutionary approach in wireless communication field in the sense

that it transmits and receives pulse based waveforms compressed in time domain rather

than frequency domain like traditional radio transmission. Figure 1.1 briefly explained

the difference between traditional narrow band systems which usually uses periodic

sinusoidal signal for communication to an UWB system which uses narrow time

domain pulse which spans over a very wide frequency band.

Figure 1.1 Difference between compressed signals in time domain

to the one expanded in time domain [2]

Due the introduction of UWB technology, the frequency spectrum allocation become

the important factor to the vendors. Thus, the Federal Communications Commission

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(FCC) has allocated the unlicensed frequency band in the range of 3.1 GHz to 10.6

GHz for UWB applications in February 2004. The allocation of the unlicensed band

giving benefits to the UWB technology. Due to this factor, there is a lot of investors

being attracted from various fields and opened the doors for the development of

numerous daily life applications based on the UWB technology.

In addition, the UWB technology is referred to the application which has an

absolute bandwidth more than 500 MHz. In other words, it can be said the system has

a relative bandwidth of greater than twenty five percent. For example, an UWB signal

centred at 2 GHz would have a minimum bandwidth of 500 MHz and minimum

bandwidth at 4 GHz would be 1 GHz. This large spread in frequency domain results

in low level of power spectral density (PSD) as depicted in Figure 1.2. This low level

of PSD ensures the peaceful coexistence of UWB systems with narrowband systems

operating in the same frequency range [3].

Figure 1.2 FCC spectral masks for outdoor unlicensed UWB emission [3]

UWB system has wide impedance bandwidth, steady directional or omnidirectional

radiation pattern, constant gain in desired direction, constant desired polarization, high

4  

radiation efficiency, linear phase response, Small size, low profile and embeddable,

low cost and low complexity (installation, fabrication, materials and maintenance).

UWB systems operate at low power transmission levels; channel capacity is proportion

to the bandwidth.

Due to the characteristics of the UWB antennas, this project had been focused

on Antipodal Vivaldi antennas. Antipodal Vivaldi antenna is one of member of taper

slot antenna which functioning as end fire and traveling wave antenna to produce a

directive radiation or omni-directional radiation pattern. The wider pattern bandwidth

and impedance will make the Vivaldi antenna as a traveling wave antenna. Besides

that, the Printed Vivaldi antennas are easy to fabricate, having no highly sensitive

dimensional tolerances. In theoretical, the Vivaldi antenna can be said has an infinity

absolute bandwidth, but it will limits by its physical size and the fabrication capability.

In practice, one of the main bandwidth limitations is the microstrip feeding technique.

1.3 PROBLEM STATEMENT

There are a few types of UWB antenna that widely used in wireless application.

P.J. Gibson was the first introduced Vivaldi antenna since 1979. There are 3 main

categories of Vivaldi antenna: Coplanar, Antipodal and Balanced antipodal that

common use in UWB application. After few years, the researchers were modified the

co-planar Vivaldi antenna by using different methods. The aim of the modification

antenna was to improve and optimize the antenna parameters. Besides, the shape and

the dimension of exterior surface of antenna will effect on the radiation field. In order

to achieve the UWB frequency, a larger size of antenna will be used. The S11

parameter known as reflection coefficient or return loss is represents how much power

is reflected from the antenna. If S11 is 0 dB, all power is reflected from the antenna

and there is no radiated power. However, S11 is -10 dB, this implies that 3 dB of power

is delivered to the antenna while -7 dB is reflected power. [8] Thus, it is important to

improve the return loss more than -10 dB in order to get greater antenna gain. In other

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words, the lower gain of antenna will bring to the increase rate of losses during

transmission. The narrower bandwidth is due to the weakness of microstrip patch

antenna. Further, the radiation field of the antenna depends on the shape and dimension

of exterior surface. In order to achieve UWB frequency, larger size antenna will be

used.

1.4 SIGNIFICANCE OF STUDY

The Vivaldi antenna is a member of the class of aperiodic, continuously scaled

and end-fire travelling wave antenna structures. It has the advantage of infinite

operating bandwidth due to its exponentially flares. In practice, it can provide

multioctave operation and is therefore designed under class of UWB antennas. These

antennas are used for several applications such as satellite communication systems,

radio astronomy, microwave imaging, feeds for reflectors and wide-band phased array

systems. Due to its smaller size, low cost, ease to fabricate and no highly sensitive

dimensional tolerance, it has been widely explored in UWB technology. In future, the

antennas of wireless applications in UWB will replace with Vivaldi antenna because

of its advantages. It can be further explore to achieve higher frequency band and the

applications.

1.5 OBJECTIVES OF STUDY

The aim of this project is to investigate and optimize the Vivaldi antenna for

UWB applications. In order to achieve this, some of the objectives need to be an

accomplished:

i. To identify the limitation of key parameters for conventional Vivaldi antenna.

ii. To improve the return loss and gain of antenna.

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iii. To analyse the simulation results at specific frequencies.

1.6 SCOPE OF PROJECT

The objective of this project is to optimize the Vivaldi antenna for UWB

application. Before design an optimization antenna, firstly we have to do the research

on the Vivaldi antenna in UWB technology. The research is based on the journals from

the internet and library. The focus of this project is to design, simulate, analyse and

compare the simulation results in order to produce an optimize antenna. The software

will be used in design and simulation the antenna is Computer Simulation Technology

(CST). There is few types of Vivaldi antenna is determined through journals from

previous researchers. From the journals, the shape of slot antenna, type of substrate

and antenna parameter will be analysed. Besides that, the improvement technique that

used for the antenna parameter is determined from the journals. A parametric study is

applied to design the optimization of Antipodal Vivaldi antenna in higher gain with

miniature size of the antenna. In addition, Roger RT 5880 is chosen as a substrate with

dielectric constant of 2.2.

1.7 THESIS OUTLINE

This thesis introduces the investigation and optimization of Vivaldi antenna for

UWB application. This overall project will be discussed in five chapters.

In Chapter 1 describes the general idea of the project which includes the

problem statement and project background. The objectives and the scopes of the

project are listed. A short and precise methodology also describes so that objectives

can be achieved.

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In Chapter 2 introduces the literature review about the previous research of

UWB technology and Vivaldi antenna. The theories of the antenna will be discussed

in this chapter.

In Chapter 3 describes a flow of the steps and methodology based on the time

frame. The modified antenna is designed using CST software. A different dimensions

of feedline and substrate are used in the designed which to differentiate from previous

researchers.

In Chapter 4 describes the simulation results will be analysed at specific

frequencies. In the simulation results, a comparison between the changes of designed

antenna will be discussed.

In Chapter 5 describes the project outcome. The overall conclusion on the

project achievement will be mentioned in this chapter. The recommendation for the

future work also will be described.

 

 

 

 

 

 

 

 

 

 

 

 

 

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CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION

In this section, the related previous work done by the researcher will be

analysed and discussed. Besides, the related theoretical part is being explained in detail.

This will help to enhance the understanding of this project and contribute towards the

completion of the project. The previous works done by researchers is one of the factors

for design this project.

2.2 BASIC ANTENNA PARAMETER

Antenna is a device which radiates or receives electromagnetic waves. The

antenna is the transition between a guiding device and free space and it is used to

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convert the energy of guided wave as efficiently as possible or vice versa. Basically,

the antenna parameters are concerned on radiation pattern, impedance bandwidth,

directivity, efficiency and gain.

2.2.1 RADIATION PATTERN

Radiation pattern is provided the information of how an antenna is directing

the energy. In far-field region, the researcher can indicate the properties of antenna

through its propagation pattern. The propagation pattern of the radiated wave is

illustrated in radiation pattern. The position of any particular point in this region has

its own direction and can determine the directivity of the radiated wave. In radiation

field, electric field and magnetic field are used in determined the pattern. The

magnitude of both fields can be expressed in dB scale.

In Figure 2.1, the shapes and direction of the lobes are shown in three

dimensional coordinates system. The x-z plane is indicated the elevation plane whereas

the x-y plane is indicated the azimuth plane.