microstrip patch beamforming linear antenna...

MICROSTRIP PATCH BEAMFORMING LINEAR ANTENNA ARRAY WITH

COMPLEMENTARY SPLIT RING RESONATOR FOR FIFTH GENERATION

APPLICATIONS

RAGHURAMAN SELVARAJU

A thesis submitted in fulfilment of the

requirements for the award of the degree of

Doctor of Philosophy

School of Electrical Engineering

Faculty of Engineering

Universiti Teknologi Malaysia

JANUARY 2019

DEDICATION

I dedicate this dissertation

To my beloved Father “Selvaraju” and Mother “Malarkodi”,

To my dearest Sister “Karthiga” for their support and encouragement.

iii

ACKNOWLEDGEMENT

I would like to express my most sincere gratitude to those who have contributed

to the present thesis. First of all, I am thankful to God Almighty for giving me the

strength, patience, and health to accomplish this thesis work. Second, I want to take

this chance to give a special thanks to my supervisor, Dr. Mohd Haizal Jamaluddin

and External co-supervisor Dr. Muhammad Ramlee Bin Kamarudin, for giving me the

opportunity to begin the Ph.D degree.

I would like to acknowledge my dear family. First of all, my dear father, who

was the first one who encouraged me to explore new things. He was the first teacher

and role model in my life. My dear mother comes next, Thanks to her for her endless

support, sacrice, and patience. I would like to thank my lovely sibling for her warm

support, and love. Finally I also would like to thank my brother-in-law Dr. Kumaran

Shanmugam, He supported me and gave me the confidence so that, I can stand tall and

face the hardships of life and find my way forward towards my goals, no matter how

hard the opposition i face.

My special thanks to my supervisor Dr. Mohd Haizal Jamaluddin, who

throughout my studies gave me great advices and knowledge, without which I would

not be able to complete this degree. During the course of this study, he supported me in

every aspect. He never hesitated, when I needed his time. Specially, I am very grateful

to my external co-supervisor Dr. Muhammad Ramlee Bin Kamarudin, who always

advised and helped me to remove any technical problems that I faced in my designing

and testing period. He always gave me new ideas and it helped to clear my ambiguities

regarding antennas.

I extend my deepest appreciation to my dearest senior Dr. Jamal Nasir for his

friendship, expert advice, support and patience through the course of this work. I can

not thank him enough for his guidance and friendly assistance that helped me improve

my technical skills and academic knowledge. I believe that having discussions with

him is a peerless privilege.

iv

I would also like to thank all my colleagues and friends, specially, Mr.

Muhammad Hashim Dahri for your endless support, love and care. I have been gifted

with lots of true friends whom I will never forget the moments that I shared with them.

Next, I must say “thanks” to Wireless Communication Centre (WCC) technical

staff Mr. Mohd Shahrul Shari, who had helped me for measurement and fabrication of

my designs during my study. Almost all experimental results in this thesis are merit

of his outstanding and patient work. Last but not the least, I would also like to thank

all the academic and technical staff of Wireless Communication Centre (WCC), FKE,

UTM. I am glad to work with such a friendly, active, and collaborative group.

My apology goes to those whom I did not include in this acknowledgment.

They will always be in my heart.

v

ABSTRACT

The next generation cellular standard which is called fifth generation (5G)

requires high gain beamforming antenna array to provide high speed and secured

communication. Therefore, the proposed research work investigates the design and

development of a four-element linear microstrip patch array operating at 25 GHz

for 5G beamforming application. To investigate the radiation characteristics of the

proposed array, five beamforming radiation patterns (main beam at 0, ±15 and

±20) have been considered. The mutual coupling between array elements raise

the challenge of designing the antenna array system. The coupling alters the array

element input impedance and distorts the overall radiation performance. Hence, a

simple complementary split ring resonator (CSRR) structure has been developed to

alleviate the coupling problem. The modeled configuration is numerically analyzed,

verified and implemented between the array elements. The existence of the CSRR

configuration in antenna array, controls the unnecessary surface current flow between

the array elements, thus the mutual coupling between array elements has been

significantly reduced from −23 dB to −55 dB. The effect of coupling on the array

radiation patterns has been studied in the presence and absence of CSRRs. Most

importantly, the effectiveness of CSRR has been studied by steering the main beam

as well as the nulls in different angles. By implementing the CSRR elements in

array antenna, the distorted array patterns have been recovered and are presented.

The proposed CSRR implemented in antenna array have the advantage of easy and

low cost fabrication and it offers excellent coupling suppression without changing the

antenna profile. Moreover, to the best of the authors knowledge, it was observed for the

first time that the CSRR worked efficiently in reducing the effect of mutual coupling

when the beam was steered off from broadside direction from −20 to +20. The

simulation tools such as MATLAB and Ansys HFSS have been used for array weights

calculation and antenna design respectively. Finally, the fabricated prototype has been

experimentally verified, and it shows that the analytical and computed results agree

well with the measured results.

vi

ABSTRAK

Piawai generasi selular yang seterusnya dikenali sebagai generasi kelima

(5G) memerlukan gandaan antena tatasusunan pembentuk alur yang tinggi bagi

menyediakan sistem komunikasi berkelajuan tinggi dan selamat. Oleh itu, cadangan

kerja penyelidikan ini adalah untuk mereka bentuk dan mengeksplotasi empat

elemen tatasusunan tampalan mikrostrip linear yang beroperasi pada 25 GHz untuk

aplikasi pembentuk alur 5G. Untuk menyelidik ciri-ciri tatasusunan radiasi yang

dicadangkan, lima corak radiasi (alur utama at 0, ±15 and ±20) pembentuk alur

telah dipertimbangkan. Gandingan saling di antara elemen tatasusunan meningkatkan

cabaran untuk mereka bentuk sistem tatasusunan antena. Gandingan tersebut

mengubah galangan masukan elemen tatasusunan dan menganggu prestasi radiasi

keseluruhannya. Oleh itu struktur penyalun gelang terpisah lengkap (CSSR) telah

dibangunkan untuk mengurangkan masalah gandingan. Model konfigurasi secara

berangka telah dianalisis, disahkan dan dilaksanakan di antara elemen tatasusunan.

Kewujudan konfigurasi CSSR di dalam tatasusunan antena mengawal aliran arus

permukaan yang tidak perlu di antara elemen tatasusunan, oleh itu gandingan saling di

antara elemen tatasusunan telah dikurangkan dengan ketara dari −23 dB hingga −55

dB. Kesan dari gandingan pada bentuk radiasi tatasusunan dikaji dengan ketiadaan

dan kehadiran CSSR. Yang paling penting, keberkesanan CSSR telah dikaji dengan

mengarahkan alur utama serta nol di dalam pelbagai sudut. Dengan melaksanakan

elemen CSSR pada tatasusunan antena, bentuk radiasi yang terganggu telah kembali

pulih dan dipersembahkan. Cadangan CSSR yang dilaksanakan di dalam tatasusunan

antena mempunyai kelebihan seperti antena mudah direka, murah dan pengurangan

gandingan yang sangat baik tanpa menukar bentuk antena. Lagipun, mengikut

kefahaman penulis, buat pertama kalinya bahawa CSSR beroperasi dengan baik sekali

dalam mengurangkan gandingan saling ketika alur itu berubah-ubah dari arah sisi

lebar, −20 kepada +20. Alat simulasi seperti MATLAB dan Ansys HFSS telah

digunakan untuk pengiraan pemberat tatasusunan dan reka bentuk antenna, masing-

masing. Akhir sekali, prototaip yang direka telah diuji secara eksperimen, dan ia

menunjukkan bahawa keputusan analitik dan pengiraan bertepatan dengan keputusan

pengukuran.

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT vi

ABSTRAK vii

TABLE OF CONTENTS viii

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF ABBREVIATIONS xviii

LIST OF SYMBOLS xx

LIST OF APPENDICES xxi

CHAPTER 1 INTRODUCTION 1

1.1 Overview 1

1.2 Problem Statement 3

1.3 Research Objectives 5

1.4 Scope of the Research 5

1.5 Research Contributions 7

1.6 Outline of the Thesis 8

CHAPTER 2 LITERATURE REVIEW 9

2.1 Overview 9

2.2 Millimeter-wave 11

2.3 Microstrip Patch Antenna 13

2.3.1 Rectangular Microstrip Patch Antenna 14

2.3.2 Transmission Line Model 15

2.3.3 Feeding Techniques 17

2.3.3.1 Coaxial Probe Feeding 17

viii

2.3.4 Radiation Characteristics 19

2.4 Antennas Array 19

2.4.1 Linear Array 20

2.4.2 Broadside Array 22

2.4.3 End-fire Array 22

2.4.4 Beam Steering Array 23

2.4.5 Beamforming Array or Smart Array 23

2.4.5.1 Switched Beamforming Ar-

rays 24

2.4.5.2 Phased Array Antenna 24

2.4.5.3 Adaptive Array Antenna 24

2.5 Computing weights for N=4 Array Using Linear

Algebra Method 25

2.6 Beamforming Arrays 28

2.7 Mutual Coupling 33

2.7.1 Open-Circuit Voltage Method 34

2.7.2 S-Parameter Method 36

2.7.3 Full-Wave (Method of Moment) 37

2.8 Metamaterials (MTM) 38

2.8.1 Defected Ground Structure 41

2.8.1.1 Concentric Ring Shaped

DGS 42

2.8.1.2 Slitted Ground Structure 43

2.8.2 Electromagnetic Band Gap Substrate 44

2.8.2.1 Mushroom-shaped EBG 45

2.8.2.2 Uni-planar EBG (UC-EBG) 50

2.8.3 Split Ring Resonator 56

2.8.4 Complementary Split Ring Resonator 66

2.9 Summary 77

CHAPTER 3 RESEARCH METHODOLOGY 79

3.1 Overview 79

3.2 Methodology of Research 79

ix

3.2.1 Mathematical Modeling, Designing

and Simulation 81

3.3 Beamforming Antenna Array Fabrication Proce-

dure 85

3.3.1 Printing 86

3.3.2 Ultraviolet Exposure 86

3.3.3 Developing and Etching 87

3.4 Beamforming Antenna Array Measurement 88

3.4.1 Scattering Parameters Measurement 89

3.4.1.1 SOLT calibration 90

3.4.2 Element Weight (Magnitude and

Phase) Measurement 91

3.4.3 Beamforming Radiation Pattern Mea-

surement 94

3.4.3.1 Azimuth plane and Elevation

plane Measurements 96

3.4.4 Gain Measurement 97

3.5 Summary 98

CHAPTER 4 BEAMFORMING ANTENNA ARRAY MATHEMAT-

ICAL MODELING SIMULATION AND MEASUREMENT 99

4.1 Overview 99

4.2 Smart Beamforming for Linear Antenna Array 99

4.3 Beamforming Antenna Array Design 101

4.3.1 Microstrip Patch Antenna Design 102

4.3.2 Simulation and Optimization 103

4.3.3 Four-element Linear Antenna Array 106

4.3.4 Effect of mutual coupling on antenna

array 109

4.3.5 Beamforming Analysis 111

4.4 Metamaterial Band Rejection Structures 116

4.4.1 Split Ring Resonator 116

4.4.2 Unit Cell Simulation 119

4.4.3 Complementary Split Ring Resonator 122

x

4.5 Mutual Coupling Reduction in Antenna Array

Using CSRR 125

4.5.1 Two Element Antenna Array With

Single Row of CSRRs 126

4.5.2 Two Element antenna Measurements 130

4.6 Mutual Coupling Reduction and Pattern Error

Correction in Beamforming Linear Array Using

CSRR 132

4.7 Beamforming Linear Antenna Array Experimen-

tal Validation 139

4.7.1 Measured Scattering Parameter Results 141

4.7.2 Beamforming Radiation Pattern Mea-

surements 142

4.8 Gain of the Four-element Beamforming Antenna

Array 145

4.9 Summary 146

CHAPTER 5 CONCLUSION AND FUTURE WORK 147

5.1 Conclusion 147

5.2 Suggestions for Future Work 149

REFERENCES 151

xi

LIST OF TABLES

TABLE NO. TITLE PAGE

Table 2.1 Performance comparison. 75

Table 2.2 Performance comparison. 76

Table 3.1 Design specification. 85

Table 3.2 Components specification. 92

Table 4.1 Microstrip patch design parameters. 102

Table 4.2 Summary of beamforming patterns. 111

Table 4.3 Array elements complex weights. 112

Table 4.4 Ideal and simulated antenna array beamforming pattern

results summary. 115

Table 4.5 SRR unit cell dimensions. 119

Table 4.6 CSRR unicell dimensions. 123

Table 4.7 Ideal and simulated antenna array beamforming pattern

results summary. 138

Table 4.8 Simulated gain of the antenna array with and without CSRRs. 139

Table 4.9 Simulated and measured gain of the antenna array with and

without CSRRs. 145

xii

LIST OF FIGURES

FIGURE NO. TITLE PAGE

Figure 2.1 Down link peak data rates for different network technologies 10

Figure 2.2 Existing services in radio frequency spectrum 11

Figure 2.3 Propagation loss measurement setup 12

Figure 2.4 ITU allocated 5G bands for mobile communication 13

Figure 2.5 Printed antenna configuration 14

Figure 2.6 Effective length of rectangular patch antenna 15

Figure 2.7 Probe fed configuration 18

Figure 2.8 N elements linear array with inter element separation S and

phase shift β 20

Figure 2.9 Four-element linear array (elements along the y-axis). 26

Figure 2.10 Eight element linear microstrip patch antenna array 29

Figure 2.11 Geometry of 1 × 4 linear array antenna with its polarization

feed network and measured results 29

Figure 2.12 Prototype of 2 × 1 antenna array with parasitic pixels and its

results 30

Figure 2.13 Prototype of the antenna array with its radiation pattern

results 31

Figure 2.14 Beam switching antenna array with normalized gain pattern 32

Figure 2.15 Mutual coupling phenomena 33

Figure 2.16 Measured radiation patterns of the dipole circular array 36

Figure 2.17 Compensated and uncompensated measured radiation pat-

terns of an antenna array with inter-element spacing of 0.517

λ 37

Figure 2.18 Materials categorization based on the sign of their ε and µ 39

Figure 2.19 Photograph of double neagtive metamaterial 40

Figure 2.20 Dumbbell shaped DGS and its equivalent circuit model 41

Figure 2.21 Simulated S-parameters of the dumbbell shape DGS with

strip line 42

Figure 2.22 Concentric ring shaped defected ground structure 42

xiii

Figure 2.23 Geometry of antenna arrays with slitted ground plane 43

Figure 2.24 S-parameters of antnnas with and without slitted ground plane 44

Figure 2.25 Mushroom EBG 45

Figure 2.26 Equivalent circuit model of the mushroom EBG 46

Figure 2.27 Patch antenna array without and with mushroom-EBG 46

Figure 2.28 S-parameters with presents and absence of mushroom EBG 47

Figure 2.29 Microstrip antennas separated by the fork like EBG 47

Figure 2.30 transmission coefficient (S21) between antenna elements with

and without fork shape EBG 48

Figure 2.31 Simulated mutual coupling results of two element antenna

array 48

Figure 2.32 Two element antenna array with dual layer mushroom EBG

and S-parameter results of antenna array 49

Figure 2.33 Uni-planar compact photonic bandgap structure 50

Figure 2.34 Wideband bow-tie shape EBG 51

Figure 2.35 Simulated and measured bandgap response of wide band UC-

EBG 51

Figure 2.36 Slotted UC-EBG and measured transmission coefficient 52

Figure 2.37 Different size EBG and transmission coefficient 53

Figure 2.38 Array of patches in a multilayer substrate with planar EBGs 54

Figure 2.39 S-parameters of antenna array with and without EBG 54

Figure 2.40 Geometry of antenna array with EBG and transmission

coefficient 55

Figure 2.41 UC-EBG unit cell loaded multiple layer antenna array and its

S-parameter results 56

Figure 2.42 Split ring resonator 57

Figure 2.43 Split ring resonator equivalent lumped circuit model 57

Figure 2.44 Broad side coupled split ring resonator and its simulation

setup 59

Figure 2.45 BC-SRR unit cell simulation results 59

Figure 2.46 Monopole antenna array with BC-SRR decoupling setup 60

Figure 2.47 Meander line antenna configuration with metasurface 61

Figure 2.48 Two element antenna array with E-SRR decoupling elements 61

xiv

Figure 2.49 S-parameter results of MLA array with and without

metasurface and separators 62

Figure 2.50 DNG unit cell with simulation setup 63

Figure 2.51 Filed distribution of sine corrugation and DNG based

AFTSA. 64

Figure 2.52 BC-SRR loaded antenna array with S-parameter results. 65

Figure 2.53 Modified SRR unit cell with two element dielectric antenna

array 66

Figure 2.54 Complementary split ring resonator and its boundary

condition 66

Figure 2.55 Complementary split ring resonator equivanet circuit model 67

Figure 2.56 SCSRR unitcell. 68

Figure 2.57 SCSRR implemented antenna array and its results 69

Figure 2.58 FSRR unit cell 70

Figure 2.59 Experimental results of simple array and FSRRs loaded

arrays 70

Figure 2.60 SCCSRR unit cell and simulation results 71

Figure 2.61 Top and bottom surface of−→E -coupled antenna array 72

Figure 2.62 S-parameter and radiation pattern results of−→E -coupled array 73

Figure 2.63 MIMO antenna with circular CSRR 73

Figure 2.64 Two element antenna array with C-shape CSRR. 74

Figure 3.1 Flowchart of beamforming array. 80

Figure 3.2 Setup for array elements weights in HFSS in volts (rms). 82

Figure 3.3 Setup for array elements weights in HFSS in power (dBm). 82

Figure 3.4 Setup for array pattern plot. 83

Figure 3.5 Setup for active element pattern plot. 84

Figure 3.6 Simulation process. 84

Figure 3.7 Ultraviolet exposure unit 86

Figure 3.8 Fabrication of the antenna array. 87

Figure 3.9 Measurement process. 89

Figure 3.10 PNA-L Network Analyzer 90

Figure 3.11 Block diagram of the beamforming setup. 91

Figure 3.12 Real time controller setup. 93

Figure 3.13 Beamforming array controller setup with PNA-L. 93

xv

Figure 3.14 Procedure of measuring magnitude and phase of S21. 94

Figure 3.15 Measurement setup for beamforming array. 95

Figure 3.16 Required orientations of the source antenna and AUT for the

measurement of azimuth and elevation plane. 96

Figure 4.1 Four-elements beamforming antenna array. 100

Figure 4.2 Four-elements beamforming antenna array. 101

Figure 4.3 Microstrip patch design parameters. 102

Figure 4.4 Patch antenna optimization results. 103

Figure 4.5 Input impedance for different values of ′Q′. 104

Figure 4.6 Reflection coefficient for different values of ′Q′. 104

Figure 4.7 Simulated reflection coefficient. 105

Figure 4.8 Simulated input impedance. 105

Figure 4.9 Simulated normalized radiation pattern. 106

Figure 4.10 Four-elements linear array. 106

Figure 4.11 S-parameters of the proposed linear array. 107

Figure 4.12 Simulated normalized radiation pattern of four-element

antenna array. 108

Figure 4.13 Current distribution in four-element antenna array. 109

Figure 4.14 Active impedance of four-element antenna array. 110

Figure 4.15 Active element patterns of the proposed array. 111

Figure 4.16 Array radiation pattern with main beam at 0. 112



Figure 4.19 Array radiation pattern with main beam at −15. 114

Figure 4.20 Array radiation pattern with main beam at −20. 115

Figure 4.21 SRR unit cell. 117

Figure 4.22 Unit cell simulation setup. 120

Figure 4.23 Scattering parameter response of SRR unit cell. 120

Figure 4.24 Effective permittivity of SRR unit cell. 121

Figure 4.25 Effective permeability of SRR unit cell. 121

Figure 4.26 CSRR unit cell. 122

Figure 4.27 Transmission coefficient (S12) for different values of ′a′. 123

Figure 4.28 Simulated results of CSRR unit cell. 123

Figure 4.29 Effective permittivity of CSRR unit cell. 124

xvi

Figure 4.30 Effective permeability of CSRR unit cell. 124

Figure 4.31 Two element antenna array. 125

Figure 4.32 Simulated S-parameter of two element array. 126

Figure 4.33 Antenna array with single row CSRR. 126

Figure 4.34 The results of antenna array without and with CSRR 127

Figure 4.35 Different orientation of CSRR elements. 128

Figure 4.36 S12 of the two-element array with different CSRR configura-

tions. 129

Figure 4.37 Prototype of the two element antenna arrays. 130

Figure 4.38 Simulated and measured S-parameter results of two element

antenna array without CSRR. 131

Figure 4.39 Simulated and measured S-parameter results of two element

antenna array with CSRR. 131

Figure 4.40 Simulated and measured radiation pattern of two element

antenna array with and without CSRR. 132

Figure 4.41 Antenna array with opposite faced CSRR elements. 132

Figure 4.42 S-parameters of the antenna array with opposite faced CSRR. 133

Figure 4.43 Current distribution in four-element antenna array with

CSRR. 133

Figure 4.44 Active impedance of CSRRs loaded four-element antenna

array. 134

Figure 4.45 Active element patterns of the CSRRs loaded array antenna

element with isolated pattern. 135

Figure 4.46 Radiation pattern with main beam at 0. 136



Figure 4.49 Radiation pattern with main beam at −15. 137

Figure 4.50 Radiation pattern with main beam at −20. 138

Figure 4.51 Fabricated four-element antenna arrays 140

Figure 4.52 Measured S-parameter results of the antenna array. 141

Figure 4.53 Beamforming radiation pattern measurement setup. 142

Figure 4.54 Measured radiation pattern with main beam at 0. 143



xvii

LIST OF ABBREVIATIONS

1G – First Generation

2G – Second Generation

3G – Third Generation

4G – Fourth Generation

5G – Fifth Generation

AEP – Active Element Pattern

AF – Array Factor

AMC – Artificial Magnetic Conductor

AOA – Angle of Arrival

AP – Array Pattern

AUT – Antenna Under Test

CSRR – Complementary Split Ring Resonator

DGS – Defected Ground Structure

DNG – Double Neagtive

EBG – Electromagnetic Band Gap Substrate

EM – Electromagnetic

EMF – Electromotive Force

Gbps – Gigabits per second

GSM – Group Special Mobile

HFSS – High Frequency Structure Simulator

HIS – High Impedance Surfaces

IMT – International Mobile Telecommunications

IoT – Internet of Things

xviii

ITU – International Telecommunication Union

Kbps – Kilobits per second

LAM – Linear Algebra Method

LMS – Least Mean Square

LTE – Long Term Evolution

Mbps – Megabits per second

MIMO – Multiple Input Multiple Output

MMS – Minimum Mean Square

mm-wave – Millimeter-wave

MTM – Metamaterial

PEC – Perfect Electric Conductor

PMC – Perfect Magnetic Conductor

RF – Radio Frequency

SINR – Signal to Interference plus Noise Ratio

SIM – Simulated

SNG – Single Neagtive

SNOI – Signal Not of Interest

SOI – Signal of Interest

S-Parameter – Scattering Parameter

SRR – Split Ring Resonator

TDMA – Time Division Multiple Access

UC-EBG – Uniplanar EBG

UHF – Ultra High Frequency

Z-Parameter – Impedance Parameter

–

xix

LIST OF SYMBOLS

AF – Array Factor

C – Capacitance

f – Frequency

k – Wave Number

L – Inductance

ε – Permittivity

β – Phase Progression

λ – Whatever

Ψ – Scalar Wave Function

γ – Angle Between Z-axis and Reference Axis

δ – Loss Tangent

ε – Permittivity

ε0 – Permittivity of Free Space

εr – Relative Permittivity

εre f f – Effective Permittivity

µ – Permeability

µ0 – Permeability of Free Space

µr – Relative Permeability

µre f f – Effective Permeability

∆l – Extended Length of Patch

θU – Angle of the Signal of Interest

θNn – Angle of the Signal not of Interest

–

xx

LIST OF APPENDICES

APPENDIX TITLE PAGE

Appendix A Ideal Array Factor and Element Weights Calculation 165

Appendix B Split Ring Resonator Resonance Frequency Calculation 171

Appendix C Permittivity and Permeability Calculation 175

Appendix D Simulation Modeling and Analysis of Microstrip Patch

Antenna With Conductive Adhesive Material 179

Appendix E Molex Cable Assembly Data Sheet and Drawing 181

Appendix F Four way Power Divider 183

Appendix G Low Noise Amplifier 187

Appendix H Analog Voltage Control Phase Shifter 191

Appendix I Voltage Control Attenuator 195

Appendix J Measured Phase Shift of The Variable Phase Shifter 199

Appendix K Measured Attenuation of The Variable Attenuator 203

Appendix L List of Publication 205

xxi

CHAPTER 1

INTRODUCTION

1.1 Overview

Historically, due the expanded wireless-communication services, the

telecommunication innovation has acquired phenomenal growth from the first

generation (1G) to fifth generation (5G). Consequently, the world wide unique mobile

subscriber numbers have exceeded up to 5 billion, and it has been expected to reach

6 billion within 2020 [1]. Furthermore, in recent years wireless gadgets and Internet

of Things (IoT) devices usage has exponentially increased. As a result of these quick

advancement the demand for mobile data services has increased a lot. Besides, the

large number of communication devices usage causes a strong interference between

the devices. In order to cope with the increased data rate demand and to address the

interference problem, a new wireless standard is required. Particularly, to support

the high-speed communication and improve the quality of services the data rate of

forthcoming wireless standard (5G) should be in the range from 100 Mbps (Edge rate)

to 1 Gbps (peak rate), respectively [2, 3].

Basically, wide operating frequency band is needed to obtain such highdata rate. Essentially, to achieve the peak data rate (10 Gbps) of the 5G, therequired frequency bandwidth must be up to several hundred megahertz or fewgigahertz [4]. However, Ultra High Frequency (UHF) band (300 MHz to 3 GHz)which is currently used for mobile communication is almost saturated due to severalapplications. Therefore, wide band allocation for future communication at UHF bandis unattainable. In the meantime, apart from UHF spectrum there are several higherfrequency spectrum bands which has strong potential to meet some of the 5G demandsidentified until now [5]. Hence, the International Telecommunication Union RadioCommunication Standards Sector (ITU-R) have allocated the frequencies above 6 GHzfor the upcoming mobile standard (5G) research [6, 7]. Recently, the millimeter-wavefrequencies have gained a substantial attention of the operators, vendors and academicresearchers, due to its unique bandwidth characteristics [6]. But, the Friis equation

1

asserts that in the higher frequencies the path loss will be increased due to its smallwavelength [8]. So that the mm-wave signals can travel only short distance andeasily deteriorated by the obstacles due to poor penetration. However, this problemcan be mitigated by employing multiple antennas (antenna array) at transmitter andreceiver ends [9]. In general, antenna array is a process of combining similar antennaelements together with a proper spacing and feeding. The array antennas possessnumerous advantages such as, high gain, narrow beam width etc. While, these arrayantennas contain limited coverage in both azimuth and elevation planes. Technicallythe coverage of the antenna array can be enhanced by utilizing beamforming technique[10].

Basically, beam-forming array is an array, which direct the maximum radiation

in the desired direction and placing nulls in the undesired directions. It has been

achieved by exciting the array elements with variable phase shift or variable time

delay [11, 12]. The beamforming array can be constructed using any type of radiating

elements. However, printed type (microstrip patch) radiators are highly suitable to

construct a compact and lightweight beamforming antenna array system. Another

interesting advantage of it is that it can be easily integrated with beam-forming circuits.

The aforementioned advantages encouraged the antenna designers to pay greater

attention on microstrip patch beamforming antenna arrays. Besides the numerous

advantages, the performance of these arrays systems is severely affected by most

common mutual coupling effects.

Mutual coupling is an electromagnetic phenomenon which exists in antennaarray when all the array elements are excited [10]. Mutual coupling in antennaarrays is under investigation for several decades. Mutual coupling alters the individualelement patterns as compared to its isolated patterns, causing mismatch, impedancevariation and correlation of the signals. This alteration depends upon the position ofthe element in the array. The result of this is a degraded array performance whichresults in the overall system performance degradation. Various mathematical methodshave been discussed in the literature to compensate the effect of mutual coupling[13, 14]. However, these mitigation methods are well suitable only for small arrays.Because, higher number of elements in an array increase the calculation complexityof these methods. Apart from the mathematical compensation methods recently, themetamaterials gained much attention in the field of electromagnetic due to its peculiarcharacteristics.

2

In general, the materials which has negative characteristics (negative electrical

permittivity or negative magnetic permeability or permittivity and permeability both

negative) are referred as meta-materials [15, 16]. Periodic arrangements of these

negative materials do not allow the surface current flow from one antenna to another,

thus the mutual coupling between antenna elements are highly reduced. Various

metamaterials configurations such as, High Impedance Surfaces (HIS) [17, 18],

Meander Line Structures [19–21], Electromagnetic Band Gap Substrate (EBG) [22–

24], Split Ring Resonator (SRR) [25, 26] and Complementary Split Ring Resonator

(CSRR) [27–29] have been reported in past studies for reducing the mutual coupling

between antenna array elements.

Specifically, among the all, the SRR and CSRR configurations offers higher

mutual coupling reduction than others. Furthermore, these structures are compact

in size, simple in design and easy to integrate with the antenna arrays. The detail

study about the split ring and complementary split ring resonators will be discussed

in the next section. In accordance with all the above discussion, the development of a

beam-forming antenna array with high gain and less mutual coupling is most essential

for future wireless (5G) system. Therefore, in this research work it is addressed in

handsome detail.

1.2 Problem Statement

The intense demand for boundless data rates has led the telecommunicationfield to implement a new wireless standard. In the meantime, the increase of usageand the demand for simultaneous communication between devices causes higherinterference. Different multiple antenna approaches like massive MIMO and beam-forming have been proposed to satisfy this ever-growing need. The MIMO systemoffers high quality of service and support large number of subscribers in single cell.However, MIMO systems are not sufficient to fulfill the high data rate need. Thebeam-forming system, which can be achieved by a one-dimensional linear or two-dimensional planar array, can further increase the channel capacity by increasingthe Signal to Interference plus Noise Ratio (SINR). Microstrip patch antennas arebeing considered as a good candidate for beamforming applications. However, the

3

performance of the microstrip patch beamforming array is severally affected due to themutual coupling.

In order to mitigate the mutual coupling and improve the performance of

the beam-forming array, different mathematical solutions like open circuit voltage

method, calibration method, receive mutual impedance approach etc. have been used.

However, for these mathematical solutions several complex measurement results are

required to mitigate the mutual coupling. Therefore, metamaterials based decoupling

structures like defected structures, electromagnetic band gap structures (EBG), split

ring resonators (SRR) and complementary split ring resonators (CSRR) are preferred.

The defected structures which could be located in ground place is large in size,

therefore it will increase the back-radiation. Next, the EBG configurations are complex

in design because multi-layer substrate and vertical via’s are required to construct

these structures. Implementing these EBGs increase the design complexity of the

beamforming array.

Compare to all, the SRR and CSRR configurations are compact and simple

designs therefore several research works proposed different CSRR configurations for

mutual coupling reduction. However, those CSRR elements were implemented in

arrays with broadside radiation pattern only and almost no study was carried out on on

the effectiveness of CSRRs in a smart beamforming array when the main beam as well

as position of nulls was changed to different angles. Hence, in this research work the

CSRR configuration is chosen to decrease the mutual coupling between beamforming

antenna array and the radiation performance of the beamforming antenna array has

been verified along with CSRR elements when the main beam and nulls are steered to

different angles. By doing so it will be justified that CSRRs not only suppress mutual

coupling when the main beam is pointing in the broadside direction (as discussed

in most studies) but are also effective when the main beam is scanned off from the

broadside direction to other angles −20to 20.

In order to address these issues, this research work focuses on two

major aspects; beamforming microstrip patch array and reducing mutual coupling

in beamforming array using complementary split ring resonators. Design of

4

beamforming microstrip patch antenna array and performance enhancement of beam-

forming array using CSRRs are discussed in Chapter 4. Moreover, in the same chapter,

the simulation and experimental results are explained in detail. Finally, the overall

work is concluded in Chapter 5.

1.3 Research Objectives

1. To model and design, a four element linear microstrip patch antenna array

operating at 25 GHz and estimate the array elements weights to perform the

beamforming.

2. To model and design, a complementary split ring resonator operating at 25 GHz

and study their band rejection characteristics.

3. To implement the configured complementary split ring resonator in between

the array elements to reduces the mutual coupling and to recover the distorted

individual element patterns and array element pattern.

1.4 Scope of the Research

The primary aims of this research are to design a beamforming antenna arrayfor next generation wireless standard application. Various frequency bands from24.25 to 86 GHz has been suggested for 5G research study [30]. The frequencyband 24.25 - 27.5 GHz have been chosen for this study with a resonant frequencyof 25 GHz. This range of frequency is the lowest possible band from the ITU-R suggested 5G frequencies, which can provide feasibility of optimized fabricationwith available beamforming RF components. Next, due to several advantages widelyused rectangular microstrip patch antenna has been used as radiating element in thisresearch. Furthermore, the coaxial probe fed method have been used to feed antennaelements because it is easy to fabricate and offer better impedance matching.

Antenna arrays come in different configurations like linear, circular, planar and

conformal. In this research work, a simple, wideband (1GHz), high gain (12dB) and

low cost linear array antenna has been proposed for 5G applications. Basically, the

5

bandwidth of the proposed antenna array is defined based on where the frequency range

S11 is less than -10 dB. Followed by, the complex array element weights (Magnitude

and Phase) has been calculated by using the array factor equation to steer the main

beam from the broadside direction to other angles −20to 20. The proposed linear

array antenna consist of four identical patch antenna elements, the four elements are

chosen because of certain short comings in purchasing expensive RF components like

attenuators, phase shifters, power dividers and amplifiers which are used to practically

provide the required magnitude and phase to the array elements for beamforming.

Generally, the mutual coupling severely degrades the performance of a smart

beamforming array. Basically, the maximum acceptable level of mutual coupling (S12)

between the array elements are considered as -15 dB. Different mathematical methods

(open circuit voltage method, decoupling method, calibration method) and use of

metamaterials based decoupling structures have been used to compensate the effect

of mutual coupling. In this work, complementary split ring resonator (CSRR) has been

chosen to reduce the mutual coupling between antenna array elements because it is

simple and compact in design and it is easy to fabricate. As a first step of mutual

coupling reduction, a simple and compact complementary split ring resonator which

has sharp band rejection at 25 GHz has been designed and analyzed. Followed by, the

surface current flow from one antenna element another is reduced by implementing the

modeled CSRR configurations in between the array elements.

After accomplishing the optimum designs, to practically investigate and

validate the concept, a four-element antenna array with and without CSRRs has been

fabricated and experimentally verified. The fabrication accuracy entirely depends on

how much accurate the design is printed on the transparent sheet. Therefore, in this

work a high quality Epson L200 ink-jet printer has been used for printer purpose. A

perfect printed output has been obtained when the dimensions of the configuration is

maintained ≥ 0.15 mm. Finally, the proposed antenna array has been experimentally

verified in terms of S-parameter and radiation pattern. The real time beamforming

setup includes several RF components which increase the losses. In order to get better

performance the losses of each RF component is properly analyzed and modeled.

6

The software used in this research work are: Matlab and Ansys HFSS.

Matlab has been used to carry out the dimension calculations of beamforming antenna

array and CSRR. Next, the Matlab has been used to calculate and verify the CSRR

constitutive parameters such us permittivity and permeability. Finally, Matlab has also

been used for the calculation of complex array element weights required for beam-

forming. Ansys HFSS has been used for the simulation and optimization of all the

beam-forming array and CSRR.

1.5 Research Contributions

The main contributions of this research work can be summarized as:

1. Innovative design of a beam-forming antenna array with four elements for 5G

application (25 GHz). This includes the fabrication and measurements of the

beamforming antenna array.

2. Innovative and compact design of complementary split ring resonator based

filtering structure. The band rejection characteristics and effective permittivity

and permeability responses are verified by numerical methods.

3. Finally, the CSRR configurations are implemented in between the array

elements to suppress the mutual coupling, by reducing the mutual coupling

the active impedance of the each array elements are exactly maintained as

50 + i0 Ω. Moreover, the distorted individual element patterns are recovered

by reducing the mutual coupling between the array elements. Therefore,

the overall array pattern which is the linear combination of element patterns

are recovered successfully. The overall results are verified by extensive

measurement procedures.

A lot of work has been done on traditional antennas for beamforming applications

and mutual coupling compensation. In this research work an extensive study has been

carried out on beamforming antenna array and the compensation of mutual coupling

effect in this antenna array.

7

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