FREQUENCY-RECONFIGURABLE ANTENNA USING ELLIPSE-SHAPED PATCH WITH DEFECTED GROUND STRUCTURE

LIM MENG CHUAN

UNIVERSITI TEKNOLOGI MALAYSIA

FREQUENCY-RECONFIGURABLE ANTENNA USING ELLIPSE-SHAPED PATCH WITH DEFECTED GROUND STRUCTURE

LIM MENG CHUAN

A thesis submitted in fulfilment of the

requirements for the award of the degree of

Master of Engineering (Electrical)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

JANUARY 2018

iii

To my beloved wife, CHONG OI LING and my daughter, TIFFANY LIM SHU YIN

iv

ACKNOWLEDGEMENT

I would like to sincere gratitude to my supervisor, Professor Ir Dr Sharul

Kamal bin Abdul Rahim for his encouragement, knowledgeable guidance, advice

and supportive in completing my master project. I would also heartfelt gratitude to

my co-supervisor, Dr Mohamad Rijal bin Hamid for his guidance, great technical

advice and assistance me to complete this master project. Besides, I would like

special thanks to Dr Ping Jack Soh, Dr Mohd Faizal Jamlos and Dr Fareq Malek

from UniMAP provide technical guidance and never say no for lab facility support.

I would also like to thank all WCC staffs for their valuable support and

discussion during my master. A special thanks to Mr. Sharul Shari and Mr.

Norhafizul Ismail for their help in order to use the facilities to measure the

performance of the antenna. A greatest appreciation to my entire friends for all the

help and assistance during my project, especially to my WCC friends, Mursyidul

Idzam Sabran, Akaa Agbaeze Eteng, Mohd Subri Abd Rani, Siti Fatimah Ausordin,

Ridduan Ramli and UniMAP friends, Nazri and Toufiq.

I want to give special appreciation to my family, especially my lovely wife

Chong Oi Ling and my adorable daughter Tiffany Lim Shu Yin for sacrifice in

family good moments to allow me to complete my part-time study. Besides, my

father Lim Yong Song, my mother Kuek Hoai Kiang, my brothers Lim Meng Chye

and Lim Meng Hai for their love, morale support and prayer along my study. Their

fully support has given me enough strength and inspiration in pursuing my ambition

as well as to complete this project.

Last but not least, special thanks to my company (INTEL) sponsor my

scholarship and my manager support throughout the study.

v

ABSTRACT

Recently, there has been an increased demand for single systems that can

handle different wireless communication applications simultaneously. Often, it is

impractical to allocate multiple antennas to the same system, so multifunctional

antennas are a critical necessity. Also, most existing frequency-reconfigurable

antennas (FRA) are made from non-transparent materials, but a transparent antenna

may be useful in scenarios where the antenna should not impair visibility.

Furthermore, wideband-to-narrowband reconfigurability has potential for use in

future cognitive radio systems. This thesis focuses on FRAs with wideband-to-

narrowband reconfigurability that use transparent and non-transparent materials. The

ultra-wideband antenna design uses an ellipse-shaped patch, thereby yielding a 7.77

GHz impedance bandwidth from 2.83 GHz to 10.66 GHz. The first FRA is obtained

by introducing a pair of annular ring slots defected ground structure (DGS) resonator

with metal switches. Its initial wideband operation mode from 3 GHz to 6 GHz can

be reconfigured into six additional bandwidth modes with a dual-band operation

centred at 3.7 GHz and 5.8 GHz and five single-band modes resonating at 4.2 GHz,

4.58 GHz, 4.86 GHz, 5.7 GHz and 6 GHz. Meanwhile, a FRA for the Wireless

Local-Area Network applications is reconfigured from a pair of rectangular DGS

resonators integrated with PIN diodes. The antenna is able to switch between a

narrowband operation centred at 5.8 GHz and a wideband operation in the range of

3.5 - 5.97 GHz. Finally, a semi-transparent antenna with a wideband-to-narrowband

frequency mode is achieved by integrating an E-shaped DGS resonator and PIN

diodes to disrupt the current flow. The antenna exhibits an impedance bandwidth

from 3 GHz to 6 GHz in the wideband mode and a resonance at 4.75 GHz when

operated in the narrowband mode. All prototypes are fabricated and measured to

verify the simulated results. The gain of antenna fabricated using the AgHT-4

transparent material is about 59% lower compared to FR-4 due to the electrical loss

of the transparent film.

vi

ABSTRAK

Pada masa kini, terdapat permintaan yang tinggi untuk sistem tunggal yang

boleh mengendalikan pelbagai aplikasi komunikasi tanpa wayar. Adalah tidak

praktikal untuk menggunakan antena yang banyak dalam satu sistem, maka antena

pelbagai fungsi adalah diperlukan. Selain itu, kebanyakan antena frekuensi boleh ubah

(FRA) dihasil daripada bahan-bahan legap, antena lut sinar mungkin berguna dalam

senario di mana antena seharusnya berprofil rendah dan lut sinar. Di samping itu,

konfigurasi frekuensi boleh ubah dari jalur-lebar ke jalur-sempit mempunyai potensi

besar untuk digunakan dalam sistem radio kognitif di masa hadapan. Penyelidikan di

dalam tesis ini tertumpu kepada antena frekuensi boleh ubah dari jalur-lebar ke jalur-

sempit dengan menggunakan bahan lut sinar dan legap. Reka bentuk antena jalur-lebar

luas menggunakan tampalan berbentuk elips menghasilkan frekuensi pada 7.77 GHz

lebar jalur galangan dari 2.83 GHz hingga 10.66 GHz. FRA pertama diperolehi dengan

memperkenalkan teknik annular ring slots defected ground structure (DGS)

menggunakan suis logam. Mod operasi jalur-lebar dari 3 GHz hingga 6 GHz boleh

dikonfigurasi ke enam mod lebar jalur tambahan dengan dua jalur berpusat pada 3.7

GHz dan 5.8 GHz, lima mod satu jalur berpusat pada 4.2 GHz, 4.58 GHz, 4.86 GHz,

5.7 GHz dan 6 GHz. Di samping itu, FRA untuk aplikasi Wireless Local-Area Network

dikonfigurasi dari sepasang DGS segi empat tepat dengan menggunakan diod PIN.

Antena boleh beroperasi di jalur-sempit yang berpusat pada 5.8 GHz dan jalur-lebar

dalam 3.5 - 5.97 GHz. Akhir sekali, antena separa lut sinar dengan mod jalur-lebar ke

jalur-sempit dicapai dengan mengintegrasikan DGS berbentuk E dan diod PIN untuk

mengganggu aliran arus. Antena ini menghasilkan lebar jalur galangan dari 3 GHz

hingga 6 GHz di dalam mod jalur-lebar dan mod jalur-sempit pada 4.75 GHz. Semua

rekabentuk yang dicadangkan telah direka dan diukur untuk mengesahkan hasil

simulasi. Nilai capaian antena yang direka menggunakan AgHT-4 lut sinar didapati

59% lebih rendah berbanding dengan FR-4 kerana sifat kehilangan elektrik filem

bahan lut sinar tersebut.

vii

TABLES OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURES xiii

LIST OF ABREVIATIONS xx

LIST OF SYMBOLS xxii

LIST OF APPENDICES xxiv

1 INTRODUCTION 1

1.1. Introduction

1.2. Problem Statement

1.3. Objectives of the Research

1.4. Scope of Work

1.5. Thesis Outline

1

2

5

5

6

2 LITERATURE REVIEW 8

2.1. Introduction

2.2. Antenna

2.2.1. Microstrip Antenna

2.2.2. Planar Monopole Antenna (3D

Profile)

8

9

10

11

viii

2.2.3. Printed Monopole Antenna (2D

Profile)

2.3. Substrate for Printed Monopole Antenna

2.3.1. Composite Substrate (Low-cost and

Low-loss) Reconfigurable Antenna

2.4. Transparent Conductive Film

2.4.1. AgHT Transparent Conductive Film

2.5. Related Research

2.5.1. UWB Antenna

2.5.2. Frequency Reconfigurable Antenna

(wideband to Narrowband)

2.5.3. Transparent Antenna

2.6. Defected Ground Structure

2.6.1. DGS Element Characteristics

2.6.2. Applications of DGS

2.7. Microwave Switches

2.8. Summary

12

12

13

14

14

15

15

17

24

30

31

32

33

35

3 RESEARCH METHODOLY 36

3.1. Introduction

3.2. Design Methodology

3.3. Material Specification

3.4. Glass (2mm) Dielectric Measurement

3.5. Simulation Tool

3.5.1. Investigate AgHT-4 Properties Setting

3.5.2. Defected Ground Structure

Optimization

3.6. Fabrication Process

3.6.1. FR-4 Antenna Fabrication

3.6.2. Semi-Transparent Antenna Fabrication

3.7. Testing and Measurement Process

3.8. Summary

36

36

38

39

43

48

50

52

54

55

56

58

ix

4 ULTRA-WIDEBAND AND FREQUENCY

RECONFIGUREABLE ANTENNA WITH NON-

TRANSPARENT MATERIALS

59

4.1. Introduction

4.2. UWB Monopole Antenna

4.2.1. Antenna Design

4.2.2. Parametric study, Results and

Discussions

4.3. Single-, Dual-, Wide-Band Frequency-

Reconfigurable Antenna Integrated with Ideal

Switches

4.3.1. Antenna Design

4.3.2. Results and Discussions

4.4. Frequency-Reconfigurable Antenna

Integrated with p-i-n Diodes

4.4.1. Antenna Design

4.4.2. Parametric study, Results and

Discussions

4.5. Summary

59

60

60

62

67

68

74

81

81

85

93

5 FREQUENCY RECONFIGURABLE ANTENNA

WITH TRANSPARENT MATERIALS

94

5.1. Introduction

5.2. Antenna Antenna Design

5.2.1. Wideband Semi-Transparent Antenna

5.2.2. Narrowband with Defected Ground

Structure

5.2.3. Investigation of Various Materials

5.2.4. Switching Method for Frequency

Reconfigurbility

5.2.5. Surface Current Distribution in

Wideband and Narrowband Modes

5.2.6. Parametric Study on Geometrical

94

95

96

99

101

103

109

111

x

Variations

5.3. Results and Discussions

5.4. Summary

117

122

6 CONCLUSION AND FUTURE WORKS

6.1. Conclusion

6.2. Recommendation for Future Work

124

124

126

REFERENCES

Appendices A-D

128

137-144

xi

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Composite Substrates (low-cost low-loss) Properties [12] 13

2.2 Properties of Standard AgHT-4 and AgHT-8 [14] 14

2.3 Review summary on UWB antenna 17

2.4 Review summary on frequency reconfigurable antenna 23

2.5 Review summary on transparent antenna 29

2.6 Comparison of performance of FET, PIN and MEMS

Switches [3] 34

3.1 Substrate specification for FR-4 39

3.2 Substrate specification for AgHT-4 39

3.3 Design specification of proposed antenna 39

3.4 Glass (2mm thickness) dielectric constant measurement 42

4.1 Parameter of UWB antenna 62

4.2 Parameters of single-, dual-, wideband frequency

reconfigurable antenna. 70

4.3 Optimum position of the switches on the annular ring in

different states 71

4.4 Gain and total efficiency for the wideband mode 77

4.5

4.6

4.7

4.8

5.1

Gain and total efficiency for the narrowband modes

Summary of the simulated and measured bandwidths for

different Modes of the Proposed Reconfigurable Antenna

Parameters of frequency reconfigurable antenna

Summary of the results for different Modes of the Proposed

Reconfigurable Antenna

Parameters of semi-transparent frequency reconfigurable

77

78

82

90

96

xii

5.2

5.3

5.4

5.5

5.6

5.7

5.8

5.9

5.10

5.11

antenna

Optimized parameters of the E-Shape DGS resonator

Summarized of various materials configuration

Simulation of S11 in ideal and real switch environment for

narrowband mode.

Surface current distribution for wideband and narrowband

modes.

Design specification of semi-transparent antenna.

Summarized results of different Ly

Summarized results of different L1, L2 and L3

Summarized results of different W1, W2 and W3

Summarized results of different LW1, LW2, LW3, LW4,

LW5 and LW6 configuration

Summary of the results for different Modes of the Proposed

Reconfigurable Antenna

100

103

107

110

111

112

114

115

116

119

xiii

LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 Vehicular ad-hoc Network [9] 4

1.2 Solar power vehicle [11] 4

2.1 Microstrip printed monopole antenna [13] 11

2.2 Various geometries of planar monopole antennas

[55]

11

2.3 Various monopole structures [55] 12

2.4 Fabricated of proposed UWB antenna [24] 16

2.5 Fabricated of proposed UWB antenna [25] 16

2.6

2.7

2.8

Slotted frequency reconfigurable antenna (a) Top

view of fabricated antenna (b) Bottom view of

fabricated antenna (c) Geometry of proposed

antenna [26]

Geometry of the proposed antenna [27]

Geometry of the selective frequency

reconfigurable antenna (a) Top view

(b) Bottom view [28]

18

20

21

2.9 Geometry and DC biasing circuit of the spiral

frequency reconfigurable antenna [29]

21

2.10 Vivaldi frequency reconfigurable antenna (a)

Top view of the geometry antenna (b) Bottom

view of the geometry antenna (c) One switch

configuration (d) Two switch configuration [30]

22

2.11 Transparent UWB antenna (a) Geometry of the

proposed antenna (b) Fabricated of the proposed

25

xiv

antenna [32]

2.12 Tapered Slot shape UWB antenna (a) Geometry

of the proposed antenna (b) Fabricated of the

proposed antenna [33]

26

2.13 Extended UWB antenna (a) Geometry of the

proposed antenna (b) Fabricated of the proposed

antenna [34]

26

2.14 Evolution of the band notch transparent antenna

(a) schematic of initial antenna (b) schematic of

implemented CSRR (c) schematic of

optimization antenna (d) Fabricated of the

proposed antenna [35]

27

2.15 CP transparent antenna (a) Geometry of the

proposed antenna (b) Fabricated of the proposed

antenna [36]

28

2.16

2.17 2.18 2.19

Fabricated of the transparent antenna

(a) ITO transparent antenna (b) Homogeneously

transparent antenna (7-nm gold) (c)

Heterogeneous transparent antenna (7-nm gold)

[38]

Semi-Transparent antenna (a) Geometry of the

proposed antenna (b) Fabricated of the proposed

antenna [64]

Some common configurations for DGS resonant

structures (a) Slot (b) Meander lines (c) Slot

variations (d) Various dumbbell shapes [59]

LCR equivalent circuit for DGS unit [57]

29

29

31

32

2.20 PIN diode (a) Structure and symbol (b) ON-

forward biased equivalent circuit (c) OFF-

reverse biased equivalent circuit [40]

34

3.1 Workflow chart of research project 37

3.2 Dielectric constant measurement

(a) Coaxial probe method (b) Dielectric constant

40

xv

measurement flow chart (c) Equipment setup for

glass dielectric constant measurement

3.3 CST® MWS® 2014 new project GUI 44

3.4 Parameter sweep setting (a) Parameter sweep

flow chart (b) Parameter list (c) Parameter sweep

function.

44

3.5 Monitor function for E-field, surface current and

Farfield

46

3.6

Step of PIN diodes simulation (a) Location of

PIN diodes (b) CST schematic GUI.

47

3.7 AgHT-4 properties investigation (a) photograph

of fabricated transparent antenna (b) S11

comparison results

48

3.8

3.9 3.10

CST® MWS® AgHT-4 library material (a)

Ohmic sheet (b) Lossy metal

Defected Ground Structure Optimization flow

chart

Fabrication process flow chart

49

51

53

3.11 UV Box Unit 54

3.12 Etching machine 54

3.13 Cameo Silhoutee Cutting tool 55

3.14 Cameo Silhoutte Studio software GUI 55

3.15 Agilent Vector Network Analyzer during S-

parameter measurement

56

3.16 DC biasing tools (a) Coin battery (CR2302)

(b) DC block BLK-18

56

3.17

3.18

Anechoic chamber during radiation pattern

measurement

Measurement process flow chart

57

58

4.1 CPW- fed UWB monopole antenna (a)

Fabricated of proposed antenna (b) Geometry of

proposed antenna

61

xvi

4.2 Comparison of reflection coefficient for ellipse

patch and ellipse patch (Ground partially

covered)

63

4.3 Comparison of reflection coefficient for different

Py

64

4.4 Comparison of reflection coefficient center

ground plane with center cut and without center

cut

64

4.5 Comparison of gain without center cut and

various Wc length

65

4.6 Comparison of reflection coefficient simulated

with measured result

66

4.7 Radiation pattern of various resonance

frequencies for proposed antenna: (a) 4.8GHz (b)

6.7GHz, and (c) 9.35GHz

66

4.8

4.9

Geometry of proposed antenna.

Simulated reflection coefficients for wideband

antenna without and with DGS (State 1)

69

69

4.10 Simulated E-field distribution 71

4.11 Geometry of the annular ring slots 71

4.12 Reflection coefficients for States 1 and 2. 72

4.13 Simulated E-field distribution at 4.4 GHz for

(a) State 1, and (b) State 2.

72

4.14 Simulated S-parameters for State 6. 73

4.15 Simulated E-field distribution of state 6 at:

(a) 2.9 GHz and (b) 6.9 GHz, and (c) 5.48 GHz

74

4.16 Photograph of fabricated antenna (Switch

configuration in State 5)

75

4.17 Simulated (solid line) vs. measured (dashed line)

reflection coefficient for the wideband mode

(state 1) and dual-band mode (state 2)

75

4.18

Simulated (solid line) reflection coefficients for

the single band mode: at 4.2 GHz (State 3), at

76

xvii

4.58 GHz (State 4), at 4.86 GHz (State 5), at 5.7

GHz (State 6), and at 6 GHz (State 7)

4.19 Measured (dashed line) reflection coefficients

for the single band mode: at 4.2 GHz (State 3), at

4.58 GHz (State 4), at 4.86 GHz (State 5), at 5.7

GHz (State 6), and at 6 GHz (State 7)

76

4.20 Simulated (solid line) and measured (dashed

line) radiation patterns in the wideband mode:

State 1 (at 4.5 GHz). (a) yz-plane, (b) xz-plane

78

4.21 Simulated (solid line) and measured (dashed

line) radiation patterns in the dual-band mode:

State 2 (at 3.7 GHz). (a) yz-plane, (b) xz-plane

79

4.22 Simulated (solid line) and measured (dashed

line) radiation patterns for the dual-band mode:

State 2 (at 5.8 GHz). (a) yz-plane, (b) xz-plane

79

4.23 Simulated (solid line) and measured (dashed

line) radiation patterns for the single-band mode:

State 4 (at 4.58 GHz). (a) yz-plane, (b) xz-plane.

80

4.24

4.25

Geometry of proposed antenna

Simulated reflection coefficients for wideband

antenna without and with DGS

82

83

4.26 Geometry of square ring resonator 84

4.27

4.28

Simulated reflection coefficient of resonator (a)

Bandpass-p-i-n diodes OFF (b) Bandstop-p-i-n

diodes ON.

Geometry of proposed antenna with DC biasing

circuit

84

85

4.29 Photograph of fabricated antenna with DC

biasing circuit

86

4.30 Simulated S11 of various types of DGS resonator 86

4.31 Current distribution of narrowband mode 87

4.32 Simulated S11 of various types of stub length 88

4.33 Simulated S11 of various types of stub location. 88

xviii

4.34

4.35

4.36

4.37

4.38

5.1

5.2

5.3

5.4

5.5

5.6

5.7

5.8

5.9

5.10

5.11

5.12

5.13

Simulated of reflection coefficient (S11) of p-i-n

diodes and ideal switch (copper)

Wideband mode reflection coefficient (S11)

simulated and measured results

Narrowband mode reflection coefficient (S11)

simulated and measured results

Simulated gain of proposed antenna.

Simulated and measured radiation pattern (a),

(c), (e) x-z plane; (b), (d), (f) y-z plane;

Narrowband mode: (a), (b) 5.8GHz; Wideband

mode: (b), (c) 3.5GHz and (e), (f) 5GHz.

Geometry and DC biasing circuit of the proposed

antenna.

Simulated S-parameter (S21) of different

materials

Geometry of the proposed WB antenna

Structure of the proposed antenna

Simulated reflection coefficient (S11) of WB

antenna

Geometry of E-Shape DGS resonator

Simulated S11 and S21 (a) L shape-Slot (b) F

shape-slot (c) E shape-slot

Proposed Narrowband antenna with E-Shape

DGS

Simulated reflection coefficient (S11) of various

materials configuration

Copper pads (ideal switches) location of

proposed antenna.

Simulated reflection coefficient (S11) by using

copper pads (ideal switches)

Simulated reflection coefficient (S11) by using

PIN didoes (real switches)

Comparison between simulated reflection

89

89

90

91

91

96

97

98

98

98

99

100

102

103

104

105

106

107

xix

5.14

5.15

5.16

5.17

5.18

5.19

5.20

5.21

5.22

5.23

coefficient (S11) by using copper pads and PIN

didoes

Simulated S11 and S21 (a) switches location (b)

bandpass (c) bandstop

Comparison of reflection coefficient (S11) for

different Ly

Comparison of reflection coefficient (S11) for

different L1, L2 and L3

Comparison of reflection coefficient (S11) for

different W1, W2 and W3

Comparison of reflection coefficient (S11) for

different LW1, LW2, LW3, LW4, LW5 and LW6

configuration

Photograph of fabricated semi-transparent

frequency reconfigurable antenna

Wideband mode reflection coefficient (S11)

simulated and measured results

Narrowband mode reflection coefficient (S11)

simulated and measured results

Simulated and measured wideband mode

radiation pattern (Left xz plane; Right yz plane):

(a) 3 GHz (b) 4 GHz (c) 4.75 GHz (d) 5.5 GHz.

Simulated and measured narrowband mode

radiation pattern (Left xz plane; Right yz plane)

at 4.75 GHz.

108

112

113

115

116

118

118

119

120

122

xx

LIST OF ABREVIATIONS

GHz - GigaHertz

MHz - MegaHertz

Gbps - Gigabits Per Second

Mbps - MegaBits Per Second

PIN - Positive Intrinsic Negative

DC - Direct Current

MEMS - Micro-Electro Mechanical System

FETs - Field-Effect Transistors

FR-4 - Flame Resistant 4

UWB - Ultra-Wideband

CP - Circular Polarization

IVC - Inter-Vehicle Communication

DRSC - Dedicated Short Range Communications

DGS - Defected Ground Structure

AgHT - Conductive Silver Coated Thin Film

Cu - Copper

FCC - Federal Communication Commission

IEEE - Institute of Electrical and Electronics Engineers

Wi-Fi - Wireless Fidelity

NFC - Near Field Communication

UHF - Ultra High Frequency

SHF - Super High Frequency

TCF - Thin Conductive Film

OLED - Organic Light Emitting Diode

ITO - Indium Tin Oxide

AgGL - Silver Grid Layer

xxi

AgNw - Silver Nano Wire

PET - Polyethylene terephthalate

CPW - Co-planar Waveguide

DRA - Dielectric Resonator Antenna

RF - Radio Frequency

NASA - National Aeronautics and Space Administration

CST - Computer Simulation Technology

VNA - Vector Network Analyzer

RL - Return Loss

dB - Decibel

dBi - Isotropic Decibel

S11 - Reflection Coefficient

S21 - Insertion Loss

DC - Direct Current

PCB - Printed Circuit Board

UV - Ultra Violet

SMA - Sub Miniature version A

CR - Cognitive Radio

BW - Bandwidth

WLAN - Wireless Local Area Network

GUI - Graphical User Interface

FRA - Frequency Reconfigurable Antenna

N/A - Not Applicable

xxii

LIST OF SYMBOLS

fH - High frequency

fL - Low frequency

fc - Center frequency

σ - Electrical Conductivity

εr - Dielectric constant substrate

εeff - Effective permittivity of substrate

tan δ - Loss Tangent

c0 - Speed of light in free space

λ0 - Free space wavelength

λg - Guide wavelength

≤ - Less then

Ω - Ohm

% - Percentage

xxiv

LIST OF APPENDICES

APPENDIX TITLE PAGE

A List of Author’s Publication 137

B AgHT Datasheet 139

C DC Block BLK-18 Datasheet 141

D Glossary 143

CHAPTER 1

INTRODUCTION 1.1 Introduction

Demand for wireless communication has progressively grown over the years.

Antennas are crucial parts of transceiver systems of wireless devices. Some modern

wireless systems are employed in multiple applications, requiring various operating

frequencies and antenna polarizations. Often, it is impractical to integrate multiple

antennas in a single transceiver system. Rather, a single antenna may be designed to

provide coverage of a wide range of frequencies. Although an ultra-wideband UWB

antenna can provide wide frequency coverage over the unlicensed 3.1 GHz to 10.6

GHz spectrum [1], it may not provide optimal signal to noise ratio performance, and

may need additional filtering to suppress unwanted interference [2]. Alternatively,

reconfigurable antennas have been proposed in recent years to provide coverage over

a wide range of frequencies.

Typically, antenna reconfigurability can be categorized in terms of radiation

pattern, polarization, and frequency. The frequency reconfigurable antenna is arguably

the most practical option as it is capable of switching its operation to the desired

frequency, instead of utilizing a number of antennas allocated for signal reception at

different frequencies. Besides improved performance, the combined multi-frequency

operation in a single antenna reduces space and cost [3]. Frequency reconfigurable

antennas can be classified into two types, namely continuous and discrete. Typically,

continuous tuning uses components like varactors, which apply electric bias to change

the antenna impedance. Discrete tuning, on the other hand, employs switches that are

2

controlled by DC biasing for ON and OFF state switching. Discrete tuning can be

achieved through the integration of devices such as PIN diodes.

Tuning mechanisms can be categorized into three major groups: mechanical

actuation, tunable materials and integrated devices. Mechanical actuation alters the

radiator shape or dimension to tune the resonant frequency. The drawback of this

method, which typically uses a motor, is that it takes longer time to actuate the motor,

besides high maintenance due to wear and tear part. Next, tunable materials changes

the inherent electrical properties such as permittivity, permeability and electrical

conductivity. The electric, magnetic or optical properties can be generally influenced

by using an external circuit. For instance, ferrites, ferroelectrics and liquid crystals are

tuned in this way. The last method for frequency reconfigurable antenna using

electronic devices in small packaging. The example of discrete tuning which includes

PIN diode, micro-electromechanical systems (MEMS), field-effect transistors (FETs)

whereas varactor can be used in continuous tuning by varying the bias voltage to

control their impedance [4]. Currently, PIN diodes are the most practical and popular

component for this technique [5]. Switching between different resonant frequencies

can be further categorized into two types; wideband-to-multiband and multiband-to-

multiband.

Presently, optically transparent antennas are uncommon in the market due to

limitations in research and the complexity of fabrication, compared with well-known

conventional antenna substrates such as FR4, Taconic and Rogers. To the best of

author’s knowledge, no frequency reconfigurable antenna implemented using

transparent materials have been presented in literature. In this research, investigation

of conventional and semi-transparent reconfigurable antennas capable of wideband

and narrowband modes will be performed. .

1.2 Problem Statement

Electronic devices enabling multiple wireless applications in one system are

widespread. The antenna is a crucial front-end device to radiate and receive radio

3

frequency signals in the transceiver to support such systems. Ultra-wideband (UWB)

antennas provide the advantage of covering wide bandwidths, from 3.1 GHz to 10.6

GHz, on a single antenna. However, within the UWB bandwidth there are various

applications for which frequency spectra have been allocated. Thus, coexistence

between the UWB transceiver and other applications within this bandwidth may

become an issue, as these other applications may interfere with the UWB transceiver.

Multiple antennas at specific frequencies can be used to overcome this problem, but at

a price of cost and space utilization. In order to mitigate unwanted interference, a

frequency reconfigurable antenna is a great candidate to use when antenna installation

space is constrained. It also useful for cognitive radio applications.

The earliest frequency reconfigurable antenna was patented in 1983 [6]. Since

then most research has focused on the use of conventional, non-transparent materials

for antennas. Lately, several systems require transparent parts to integrate with other

structures in the environment in order to reduce visual obstruction [7], for instance, in

energy harvesting applications [8]. Other examples are the Inter-Vehicle

Communication (IVC) and solar powered vehicle applications. IVC will be the next

generation vehicle communication system, and it employs dedicated short range

communications (DRSC). It provides inter-vehicle communication, and is beneficial

as a vehicle safety mechanism in road scenarios as depicted in Figure 1.1 [9]. There is

the possibility that cognitive radio technology can be applied to IVC in sensing and

spectrum allocation scheme for information sharing between vehicles [10]. In addition,

these vehicles could be solar powered, where energy is obtained through photovoltaic

cells installed on top of vehicle shown as Figure 1.2 [11]. Such vehicles would benefit

from the use of transparent antennas to facilitate IVC, so as not to interfere with the

solar irradiation on the photovoltaic cells.

Previous researches on transparent antennas have addressed the scopes of

UWB, dual-band, circular polarized (CP), and band notched antenna designs.

Currently, there is a gap in literature on the development of frequency reconfigurable

antennas using transparent materials. Therefore, this thesis addresses the design of

frequency reconfigurable antenna by utilizing FR-4 and AgHT-4 which provides

wideband-to-narrowband reconfigurability. Such antenna can be potentially applied in

future IVC scenarios involving solar vehicles.

4

Figure 1.1: Vehicular ad-hoc Network [9]

Figure 1.2: Solar power vehicle [11]

5

1.3 Objectives of the Research

The objectives for this study are stated as follows:

i. To design, fabricate, and analysis the wideband-to-narrowband

frequency reconfigurable antenna by implementing defected ground

structure (DGS) resonator.

ii. To investigate the performance of frequency reconfigurable antenna by

applying transparent materials that is potential implement in future

wireless communication.

1.4 Scope of Work

This study is focused on frequency reconfigurable antenna with wideband-to-

narrowband reconfigurability. Two different antenna designs are implemented in this

work, namely non-transparent antenna and a semi-transparent antenna. The non-

transparent antenna utilizes FR-4 material for the antenna design, while the semi-

transparent antenna employs AgHT-4, copper and glass.

In the first stage, a non-transparent antenna design for UWB is developed. The

basic geometry of the UWB antenna is used for subsequent antenna designs. This is

followed by the design of frequency reconfigurable antennas with single-, dual- and

wideband reconfigurablity by adding defected ground structure (DGS) annular ring

slots, with ideal switches in between the slots. Next, the DGS square slots with stubs

are used with the implemented PIN diodes, and the effect of the stubs and switches are

investigated. In the second stage, a semi-transparent antenna is developed by

employing DGS with E-shaped slot. Various configuration of materials and parametric

studies are analysed.

The CST© Microwave Studio is the main design simulation software used prior

to antenna fabrication and measurement. The antenna parameters of the wideband-to-

6

narrowband mode are analyzed in terms of reflection coefficient, gain, radiation

pattern, and bandwidth of the antenna. Lastly, all the simulated and measured results

are plotted to validate the actual performances.

1.5 Thesis Outline

This thesis contains a total of six chapters which discuss various aspects of this

research project. The thesis outline is briefly described as follows:

Chapter 1 presents an introduction and the basis of the frequency reconfigurable

antenna, problem statement, research objective and scope of work.

Chapter 2 discusses types of non-transparent antenna substrates as well as an emerging

transparent material – silver coated conductive film (AgHT). Literature review of

previous related works is important in this section for knowledge absorption to apply

in this research project. There are few types of antennas discussed, which include

UWB antennas, frequency reconfigurable antennas and transparent antennas.

Chapter 3 divides into a few sub-chapters to explain the methods of antenna designs,

starting with literature review until data analysis. Additionally, some experiments

carried out to define material properties for uncertain materials are described. The

material properties of note include the dielectric constant and resistance sheet of

material. The Chapter also discusses the fabrication technique for FR-4 and semi-

transparent antenna substrates.

Chapter 4 presents the steps to design a UWB antenna, leading to frequency

reconfigurable antenna and prior to the development of semi-transparent antenna. This

chapter discusses three antennas which are the UWB, frequency reconfigurable

antenna integrated with metal switches (ideal switch) proof-of-concept, and the

frequency reconfigurable antenna with wideband-to-narrowband 5.8 GHz

reconfigurability. In this chapter, performance of antennas will be discussed in terms

of parameters like s-parameters, radiation pattern and gain.

7

Chapter 5 focuses on the development of semi-transparent frequency reconfigurable

antenna using AgHT-4 thin film, copper and glass. There is the final step in the

evolution of the proposed antenna, from UWB to frequency reconfigurable antenna

integrated with PIN diodes (Chapter 4). The E-Shape DGS is introduced into the CPW

ground-plane for pre-filtering circuit at 4.75 GHz narrowband and switchable to

wideband mode from 2 GHz to 6 GHz. Different material configurations and

parametric studies are discussed and analysed. The simulation and measurement

results for s-parameters and radiation pattern are presented.

Chapter 6 is the last chapter, and presents a conclusion and recommendation for future

works.

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