CENTRE FOR APPLIED RESEARCH IN ELECTRONICS INDIAN INSTITUTE OF TECHNOLOGY DELHI

P LANAR A NTENNA D ESIGNS FOR

M ULTIPLE I NPUT M ULTIPLE O UTPUT S YSTEMS

D

S

CENTRE FOR APPLIED RESEARCH IN ELECTRONICS INDIAN INSTITUTE OF TECHNOLOGY DELHI

APRIL 2019

© Indian Institute of Technology Delhi (IITD), New Delhi, 2019

FOR

M ULTIPLE I NPUT M ULTIPLE O UTPUT S YSTEMS

by

D

S

Centre for Applied Research in Electronics

Submitted

in fulfillment of the requirements of the degree of Doctor of Philosophy

to the

INDIAN INSTITUTE OF TECHNOLOGY DELHI

APRIL 2019

Dedicated

to

My Family and Teachers

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CERTIFICATE

This is to certify that the work reported in this thesis entitled, “Planar Antenna Designs for Multiple Input Multiple Output Systems”, being submitted by Ms. Deepika Sipal for the award of the degree of Doctor of Philosophy to the Centre for Applied Research in Electronics, Indian Institute of Technology Delhi, New Delhi, India, is a record of original bonafide research work carried out by her under my guidance and supervision. The results contained in this thesis have not been submitted in part or full, to any other university or institute for the award of any degree or diploma.

I certify that she has pursued the prescribed course of research.

Dr. Mahesh P. Abegaonkar

Associate Professor

Centre for Applied Research in Electronics (CARE), Indian Institute of Technology Delhi (IITD),

Hauz Khas, New Delhi-110016, India.

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ACKNOWLEDGEMENTS

I am very grateful to GOD ALMIGHTY, without His graces and blessings this study would not have been possible. Immeasurable appreciation and deepest gratitude for technical help and moral support are extended to the following persons who in one way or another have contributed in making this study possible.

First and foremost I would like to express sincere gratitude to my supervisor, Dr. Mahesh P.

Abegaonker for giving me opportunity to work under his supervision in this esteemed institute. I am deeply indebted to him and sincerely thank him for his continuous support, encouragement, suggestions and discussion. His guidance, motivation and critical evaluation of my work at every stage lead to successful completion of this dissertation. I could not have imagined having a better advisor and mentor for my Ph. D study.

I would like to express my profound gratitude to Prof. Shiban K. Koul for insightful suggestions, motivation and support given to me throughout my research work. I also like to offer my special thanks to Prof. Ananjan Basu for his critical advice, suggestions and support for my research work. I want to sincerely thank Dr. Karun Rawat for his advice and motivation toward my research goals.

Besides the faculty members of RF and Microwave group, I would also like to thank Prof. Arun Kumar, Dr. Kushal Shah and Prof. Manav Bhatnagar for evaluating my research work and giving suggestions and insightful comments as members of my student research committee.

I thank my colleagues in RF and Microwave group, Dr. Manoj Singh Parihar, Dr. Madhur Deo Upadhyay, Dr. Lalitendra Kurra, Dr. Sukomal Dey, Dr. Ritabrata Bhattacharya, Dr. Surjana Kagita, Dr. Khalid Muzaffar, Dr. Ankita Adharsh Malhotra, Dr. Richa Bharadwaj, Dr. Robin

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Kalyan, Sanjeev Kumar, Dr. Saurabh Pegwal, Dr. Rajesh Kumar, Dr. Ayushi Berthwal, Anushruti Jaiswal, Santosh Bhagat, Dr. Amit Kumar, Pranav Kumar, Shakti Singh, Harikesh, Ms. Rakhe Kumari, Zamir Wani, Sriparna De, Karthekeya G.S., Swapna S., Somia Sharma, Ashish Jindal, Priyansha, Iqram for making so many memories and building base of lifelong friendship in these years. Their presence has made my journey of Ph. D. a pleasant experience in IITD.

Next, I thank Mr. Vinod Sharma, Mrs. Sneh Kapoor, Mr. S.P. Chakraborty, Mr. Ashok Pramanik, Mr. Pradeep Saxena for their support and help during my research work.

I would also like to extend my thanks to all the faculty and office staff members of CARE, who helped me in various official documental works during my Ph. D.

Last but not the least, I express my heartfelt thanks to my family and friends for their continuous encouragement in every step of my Ph. D. for which I am forever grateful to them.

DEEPIKA SIPAL

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ABSTRACT

This dissertation presents the design and development of compact planar antennas for multiple input multiple output (MIMO) systems. In the MIMO system, size of antenna element plays very important role due to demand of very compact and lightweight portable wireless devices. This thesis presents novel designs which are very compact than the state-of-the-art designs. Moreover, the proposed MIMO antenna designs are characterized in three categories based on its operating frequencies, i.e., ultra wide band (UWB) antennas, notched UWB antennas and dual band antennas. Furthermore, the proposed MIMO antenna designs can also be characterized in three categories based on its application, i.e., for USB dongle, personal digital assistant devices and access point. These MIMO antenna designs are simulated in 3-D electromagnetic (EM) simulation tool and the simulated results are verified in measurements and calculations.

This thesis is broadly divided into five parts. In the first part, the thesis deals with UWB MIMO antenna designs which covers 3.1 to 10.6 GHz band. However, presence of already existing wireless standards, such as WiFi and WiMAX, causes interference in the UWB communication system. Therefore, in second part of the thesis notched bands (single notched band at WiFi band and dual notched bands at WiFi and WiMAX bands) are incorporated in UWB MIMO antenna designs. Usually, due to size constraints of the portable devices, antenna elements are placed at closed proximity, which results in very high coupling between antennas.

Therefore, decoupling circuits are used in between antenna elements to achieve high isolation.

However, presence of these decoupling circuits occupies more space on printed circuit board and makes it difficult to deploy in the compact portable devices. On the other hand, MIMO antenna requires four to eight or more numbers of antenna elements for access point application.

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However, due to the presence of the decoupling or isolating circuit it is difficult to increase the numbers of antenna elements in the MIMO antenna system, because existing decoupling or isolating circuit does not show desired performance as numbers of antennas are increased.

Therefore, each time as numbers of antennas is increased or decreased for a particular application, the decoupling circuit needs to be modified. Modification of the decoupling circuit gets very complex in such situations. Therefore, in third part of the thesis, decoupling circuit free easily extendable UWB MIMO antenna designs has been discussed.

It has been universally accepted that all the future wireless communication devices will be having MIMO antenna deployed in it. Therefore, all the existing wireless standard based devices also need to be modified by placing multiple antennas in its antenna system. However, some of the devices already have it. A compact multi-functional wireless device, which satisfies more than one standard, is one of the promising candidates for future wireless communication system. Therefore, second last part of the thesis discusses about compact planar dual-band MIMO antenna designs, which operate in WiFi and WiMAX standards. Moreover, a dual-band MIMO antenna design becomes more adaptive when it can be reconfigured electronically by using PIN diodes. Therefore, the final part of the thesis presents frequency reconfigurable dual- band MIMO antenna design for USB dongle applications. The proposed frequency reconfigurable dual band MIMO antenna design operates in selected dual band at a time.

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साय

महशोधप्रफॊध भल्टीऩर इनऩुटभल्टीऩरआउटऩुट (भीभो) ससस्टभ के सरएकॉम्ऩैक्टप्रेनय एॊटेनाकेडडजाइनऔयविकासकोप्रस्तुतकयताहै। भीभो ससस्टभभें, फहुतकॉम्ऩैक्टऔयहल्केऩोटेफर

िामयरेस उऩकयणोंकीभाॊगके कायणएॊटेना काआकायफहुतभहत्िऩूणणबूसभकाननबाताहै। महथीससस एसे नए डडजाइनोंकोप्रस्तुत कयती है जो अत्माधुननक डडजाइनोंकी तुरनाभें फहुतकॉम्ऩैक्ट हैं। इसके

अरािा, प्रस्तावित भीभो एॊटेनाडडजाइनों कोइसकीऑऩयेटटॊगआिृत्त्तमों के आधायऩय तीनश्रेणणमों भें

यखा गमा है, मानी अल्रा िाइड फैंड (मूडब्लल्मूफी) एॊटेना, नॉचड मूडब्लल्मूफी एॊटेना औय डुअर फैंड एॊटेना।

औय तो औय, प्रस्तावित भीभोएॊटेना डडजाइनों को इसके अनुप्रमोग के आधाय ऩय तीन औयश्रेणणमों भें

बी यखा जा सकता है, अथाणत ्, मुएसफी डोंगर, व्मत्क्तगत डडत्जटर सहामक उऩकयणों औय एक्सेस प्िाइॊट भें उऩमोग केसरए। इनभीभोएॊटेनाडडजाइनोंको 3-D इरेक्रोभैग्नेटटक (ईएभ) ससभुरेशनटूर भें ससम्मुरेटककमागमाहैऔयससम्मुरेटेडऩरयणाभोंकोभाऩऔयगणनाभें सत्मावऩतककमागमाहै।

मह थीससस भोटे तौय ऩय ऩाॉच बागों भें विबात्जत है। ऩहरे बाग भें, थीससस मूडब्लल्मूफी भीभो

एॊटेना डडजाइन कोप्रस्तुतकयता है, जो 3.1 से 10.6 गीगाहर्ट्ण़फैंडको किय कयताहै। हाराॊकक, ऩहरेसे

भौजूद िामयरेस भानकों, जैसे िाईपाई औय िाईभैक्स की उऩत्स्थनत, मूडब्लल्मूफी सॊचाय प्रणारी भें

हस्तऺेऩ का कायण फनती है। इससरए, थीससस के दूसये बाग भें नॉचड फैंड (िाईपाई फैंड ऩय ससॊगर नॉचडफैंडऔय िाईपाई/िाईभैक्सफैंडभें दोहये नॉचडफैंड) कोमूडब्लल्मूफीभीभोएॊटेनाडडजाइनोंभें शासभर ककमा गमा है। आभतौय ऩय, ऩोटेफर उऩकयणों भें जगह की कभी के कायण, एॊटेनाओ को फहुत ननकट यखा जाता है, त्जसके ऩरयणाभस्िरूऩ एॊटेनाओ के फीच फहुत अधधक मुग्भन होता है। इससरए, उच्च अरगाि कोप्राप्त कयनेके सरएएॊटेनाओ केफीच डडकऩसरॊगसककणटकाउऩमोगककमाजाता है।हाराॊकक, इनडडकऩसरॊगसककणटकी उऩत्स्थनतप्रिन्टिड सककणटफोडणऩयअधधक जगह घेयतीहै औय कॉम्ऩैक्टऩोटेफर डडिाइसों भें इनका उऩमोग कयना भुत्ककर होता है। दूसयी ओय, भीभो एॊटेना को एक्सेस प्िाइॊट

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एत्प्रकेशनभें उऩमोगकयने केसरएचायसेआठमाअधधक एॊटेनाओ कीआिकमकताहोतीहै।हाराॊकक, डडकऩसरॊगमा आइसोरेटटॊग सककणट कीउऩत्स्थनत के कायण भीभोएॊटेना ससस्टभ भें एॊटेनाओ कीसॊख्मा

फढानाभुत्ककर है, क्मोंकक जफएॊटेनाओ कीसॊख्मा फढ जाती है तो भौजूदा डडकऩसरॊगमा आइसोरेटटॊग सककणटिाॊनिततरीके से काभ नहीॊ कयतेहैं। इससरए, हयफायजफककसीविशेष उऩमोगकेसरएएॊटेनाओ कीसॊख्माफढाईमाघटाईजातीहै, तोडडकऩसरॊगसककणटकोसॊशोधधतकयनेकीआिकमकताहोतीहै।ऐसी

त्स्थनतमोंभें डडकऩसरॊग सककणटकासॊशोधनफहुतजटटरहोजाता है।इससरए, थीससस केतीसये बागभें, डडकऩसरॊगसककणटभुक्तआसानीसेविस्तायमोग्ममूडब्लल्मूफीभीभोएॊटेनाडडजाइनोंऩयचचाणकीगईहै।

महसािणबौसभकरूऩसेस्िीकायककमागमाहै ककबविष्मकेसबीिामयरेससॊचायउऩकयणोंभें

भीभोएॊटेना रगा होगा। इससरए, सबी भौजूदािामयरेस भानक आधारयत उऩकयणोंको बीअऩने एॊटेना

ससस्टभभें कईएॊटेनायखकयसॊशोधधतककमाजानाचाटहए।हाराॊकक, कुिउऩकयणोंभें महऩहरेसेहीहै।

एक कॉम्ऩैक्ट फहुआमाभी िामयरेस डडिाइस, जो एक से अधधक भानको कोसॊतुष्ट कयता है, बविष्म के

िामयरेस सॊचायप्रणारीकेसरएआशाजनक उम्भीदिायोंभें सेएकहै। इससरए, थीसससकादूसयाअॊनतभ बागकॉम्ऩैक्टप्रेनयडुअर-फैंडभीभोएॊटेनाडडजाइनोंकेफायेभें चचाणकयताहै, जोिाईपाईऔयिाईभैक्स भानकोंभें काभकयतेहैं। इसकेअरािा, एकदोहया फैंडभीभोएॊटेनाडडजाइनअधधक अनुकूरहोजाताहै

जफ इसे वऩन डामोड का उऩमोग कयके इरेक्रॉननक रूऩ से ऩुन: कॉत्फ़िगय ककमा जा सके। इससरए, थीसससकाअॊनतभबाग मूएसफीडोंगर अनुप्रमोगोंकेसरएफ़्रीक्िेंसीयीकॊकपगयेफरदोहयाफैंडभीभोएॊटेना

डडजाइन को प्रस्तुत कयता है। प्रस्तावित फ़्रीक्िेंसी यीकॊकपगयेफर डुअर फैंड भीभो एॊटेना डड़ाइन एक सभमभें चमननतड्मूरफैंडभेंकाभकयताहै।

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TABLE OF CONTENTS

CERTIFICATE ... i

ACKNOWLEDGEMENTS ... ii

ABSTRACT ... iv

TABLE OF CONTENTS ... viii

LIST OF FIGURES ... xvi

LIST OF TABLES ...xxv

Chapter-1 INTRODUCTION ... 1

1.1 Motivation ... 1

1.2 MIMO technology ... 1

1.3 Antennas for MIMO system ... 3

1.3.1 Spatial diversity of antenna elements ... 3

1.3.2 Polarization diversity of antenna elements ... 4

1.3.3 Pattern diversity of antenna elements ... 4

1.4 Characterization of MIMO antenna ... 5

1.4.1 Return loss and isolation ... 5

1.4.2 Correlation coefficient ... 6

1.4.3 Diversity gain ... 7

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1.4.4 Channel Capacity Loss ... 8

1.5 Applications of the MIMO antennas ... 8

1.6 Targeted frequency range and applications ... 9

1.6.1 Targeted range of frequencies ... 9

1.6.2 Targeted application of the MIMO antenna... 11

1.7 Literature survey of state-of-the-art MIMO antenna designs ... 12

1.7.1 State-of-the-art of UWB MIMO antenna ... 12

1.7.2 State-of-the-art of multi band MIMO antenna ... 20

1.7.3 State-of-the-art of frequency reconfigurable MIMO antenna ... 23

1.8 Scope and objective of the work ... 26

1.9 Thesis Organization... 27

Chapter-2 UWB MIMO ANTENNA DESIGN ...29

2.1 Introduction ... 29

2.2 Design-I: UWB MIMO antenna for portable devices ... 30

2.2.1 Configuration and geometry of the UWB MIMO antenna ... 30

2.2.2 Parametric analysis of main parameters of the proposed MIMO antenna ... 31

2.2.3 Results and discussions ... 33

2.2.4 Comparison of UWB MIMO antenna designs... 37

2.3 Design-II: UWB MIMO antenna for USB dongle application ... 37

2.3.1 Configuration of UWB MIMO antenna for USB dongle application... 38

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2.3.2 Fabricated antenna and its S-parameter ... 40

2.3.3 Radiation pattern of the UWB MIMO USB dongle antenna ... 41

2.3.4 Envelope correlation coefficient of the UWB MIMO antenna ... 42

2.3.5 Simulated total efficiency and measured gain of the MIMO antenna ... 43

2.3.6 Comparison of UWB MIMO USB dongle antenna designs ... 44

2.4 Design guidelines for UWB MIMO antenna design ... 44

2.5 Conclusion ... 46

Chapter-3 SINGLE AND DUAL BAND NOTCHED UWB MIMO ANTENNA DESIGN...47

3.1 Introduction ... 47

3.2 Design-I: Two-element UWB MIMO antenna with notch at 5.5 GHz ... 48

3.2.1 Single UWB antenna... 48

3.2.2 Two-element UWB MIMO antenna configuration... 50

3.2.3 Enhancement of isolation of the UWB MIMO antenna ... 52

3.2.4 2-D radiation patterns of the UWB MIMO antenna ... 55

3.2.5 Envelope correlation coefficient (ECC) and diversity gain of the MIMO antenna 57 3.2.6 Gain and efficiency of the UWB MIMO antenna ... 58

3.2.7 Comparison of single band-notched UWB MIMO antenna designs ... 59

3.3 Design-II: Two-element UWB MIMO antenna with notch at 3.8 and 5 GHz for dongle application ... 60

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3.3.1 Two element UWB MIMO antenna configuration ... 60

3.3.2 Selected configuration of the UWB MIMO antenna ... 61

3.3.3 Incorporation of common and extended ground plane in the MIMO antenna ... 61

3.3.4 Incorporation of dual notched bands in the UWB MIMO antenna ... 64

3.3.5 S-parameter of the fabricated proposed dual band-notched UWB MIMO antenna 67 3.3.6 Radiation pattern of the MIMO antenna ... 70

3.3.7 Envelope correlation coefficient, total efficiency and gain of the MIMO antenna 70 3.3.8 Comparison of dual-band notched UWB MIMO antenna designs ... 72

3.4 Design-III: Four-element UWB MIMO antenna with notch at 3.3 and 5.5 GHz for compact portable devices ... 73

3.4.1 Single UWB antenna element with notch at 3.3 and 5.5 GHz ... 73

3.4.2 Initial four element dual band notched UWB MIMO antenna configuration ... 75

3.4.3 Final four element dual band notched UWB MIMO antenna configuration ... 77

3.4.4 S-parameter of the proposed fabricated prototype ... 79

3.4.5 2-D radiation pattern of the dual notched UWB MIMO antenna ... 80

3.4.6 Diversity performance of the MIMO antenna prototype ... 82

3.4.7 Gain and total efficiency of the UWB MIMO antenna ... 82

3.4.8 Comparison of dual-band notched UWB MIMO antenna designs ... 84

3.5 Design guidelines for band notched UWB MIMO antenna design ... 85

3.6 Conclusion ... 87

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Chapter-4 DECOUPLING CIRCUIT FREE EASILY EXTENDABLE

UWB MIMO ANTENNA ARRAY ...89

4.1 Introduction ... 89

4.2 Design-I: (3.6-10.6 GHz) UWB MIMO antenna array ... 90

4.2.1 Single element of the array ... 90

4.2.2 Initial 2-element UWB MIMO antenna array ... 91

4.2.3 Impedance bandwidth improvement of the 2-element UWB MIMO antenna array ………..92

4.2.4 Fabricated design of 2-element UWB MIMO antenna array... 94

4.2.5 Fabricated design of 4-element UWB MIMO antenna array with its S-parameter 95 4.2.6 Polarization/pattern diversity performance of the MIMO antenna ... 96

4.2.7 Radiation efficiency, peak gain and envelope correlation coefficient of antenna .. 99

4.2.8 Comparison of UWB MIMO antenna array designs ... 100

4.3 Design-II: (3-15 GHz) UWB MIMO antenna array... 101

4.3.1 Single element of the UWB MIMO antenna array ... 101

4.3.2 Initial 4-element UWB MIMO antenna array configuration ... 102

4.3.3 Final 4-element UWB MIMO antenna array configuration ... 104

4.3.4 Fabricated design of the UWB MIMO antenna array ... 106

4.3.5 Radiation pattern of the array ... 108

4.3.6 Gain and total efficiency of the antenna ... 109

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4.3.7 Group delay of the UWB MIMO antenna ... 110

4.3.8 Envelope correlation coefficient and channel capacity loss of the array ... 110

4.3.9 8-element UWB MIMO antenna array ... 111

4.3.10 Comparison of UWB MIMO antenna array designs ... 114

4.4 Design guidelines for decoupling circuit free easily extendable UWB MIMO antenna design.………...115

4.5 Conclusion ... 117

Chapter-5 DUAL BAND MIMO ANTENNA DESIGN ...119

5.1 Introduction ... 119

5.2 Design-I: 3.5/5.5 GHz Dual band MIMO antenna structure ... 120

5.2.1 Design analysis of the dual band MIMO antenna design ... 120

5.2.2 Simulated surface current distribution of the proposed MIMO antenna ... 124

5.2.3 Measurement of S-parameter ... 124

5.2.4 Radiation pattern measurement ... 126

5.2.5 Envelope correlation coefficient, total efficiency and gain of MIMO antenna .... 127

5.2.6 Comparison of dual-band MIMO antenna designs ... 128

5.3 Design-II: 2.4/5 GHz dual-band MIMO antenna structure ... 129

5.3.1 Design Analysis of Dual-Band MIMO Antenna ... 130

5.3.2 Parametric analysis of the dual-band MIMO antenna ... 134

5.3.3 Variation in parameter PM1 to achieve upper band ... 134

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5.3.4 Variation in parameter PM2 to achieve lower band ... 134

5.3.5 S-parameter measurement ... 134

5.3.6 Radiation pattern measurement ... 137

5.3.7 Diversity performance analysis... 138

5.3.8 Total efficiency, ECC and peak gain ... 139

5.3.9 Comparison of 2.4/5 GHz dual-band MIMO antenna designs ... 139

5.4 Design guidelines for dual band MIMO antenna design... 140

5.5 Conclusion ... 143

Chapter-6 FREQUENCY RECONFIGURABLE DUAL BAND MIMO ANTENNA DESIGN...144

6.1 Introduction ... 144

6.2 Proposed MIMO antenna configurations ... 146

6.3 Evolution of the MIMO Antenna Configurations with its working mechanism... 147

6.4 Parametric analysis of critical geometric parameters of the proposed dual-band MIMO antenna ... 153

6.5 Simulated surface current distribution of the MIMO antenna without and with decoupling circuit ... 158

6.6 Fabricated structures and its S-parameters ... 160

6.7 Reconfiguration of the dual-band MIMO antenna from config-1 to config-2 ... 162

6.8 Biasing circuit of the diode ... 164

xv

6.9 ON and OFF-states of the frequency reconfigurable dual-band MIMO antenna ... 165

6.10 Results and discussion of the frequency reconfigurable MIMO antenna ... 165

6.10.1 Fabricated frequency reconfigurable MIMO antenna and its S-parameter ... 166

6.10.2 Radiation pattern of the frequency reconfigurable MIMO antenna ... 168

6.10.3 ECC, total efficiency and gain of the frequency reconfigurable MIMO antenna . 172 6.11 Comparison of dual-band MIMO antenna designs ... 173

6.12 Design guidelines for Frequency Reconfigurable Dual-Band MIMO Antenna Design ………...175

6.13 Conclusion ... 176

Chapter-7 CONCLUSION AND FUTURE SCOPE ...177

7.1 Summary of the Thesis ... 177

7.2 Conclusion ... 179

7.3 Future Scope of the work ... 180

REFERENCES ...182

APPENDIX-I ...194

APPENDIX-II ...199

PUBLICATIONS ...200

BRIEF BIO-DATA OF THE AUTHOR ...201

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LIST OF FIGURES

Fig. 1.1. Technological advances from SISO to MIMO communication system. ... 2 Fig. 1.2. Diversity techniques incorporated in MIMO antenna design (a) spatial diversity (b) polarization diversity (c) pattern diversity. ... 4 Fig. 1.3. UWB MIMO antenna (a) schematic design and (b) fabricated design [24] ... 13 Fig. 1.4. Structure of UWB MIMO antenna design (a) schematic design and (b) fabricated design.[22] ... 14 Fig. 1.5. Single notched band UWB MIMO antenna (a) schematic design and (b) fabricated design [31]. ... 14 Fig. 1.6. Single notched band UWB MIMO antenna with its fabricated structure (a) 2-element array and (b) 4-element array [26]. ... 15 Fig. 1.7. Dual-band notched UWB MIMO antenna (a) schematic design and (b) fabricated design [34]. ... 17 Fig. 1.8. (a) Schematic of dual-band notched UWB MIMO antenna design (b) Band pass filter (c) Complementary split ring resonator (d) Fabricated dual band notched UWB MIMO antenna design [32]. ... 17 Fig. 1.9. (a) UWB MIMO antenna top view (b) UWB MIMO antenna bottom view (c) Decoupling circuit (d) fabricated UWB MIMO antenna design [36]. ... 18 Fig. 1.10. Eight-element UWB MIMO antenna array (a) schematic design and (b) fabricated design [37]. ... 19 Fig. 1.11. WLAN band MIMO antenna (a) schematic design (b) fabricated design [38]. ... 21 Fig. 1.12. WLAN band MIMO antenna for USB dongle application (a) schematic design, (b) zoomed view of schematic design and (c) fabricated design [39]. ... 21 Fig. 1.13. Dual band MIMO antenna for USB dongle application (a) proposed two antenna system, (b) shape of the ground plane and (c) fabricated design [40]. ... 22 Fig. 1.14. Planar dual band MIMO antenna (a) top view (b) bottom view (c) planar spiral line (d) fabricated structure [41]. ... 23 Fig. 1.15. CPW feed dual band reconfigurable MIMO antenna (a) schematic design (b) fabricated design [42]. ... 24

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Fig. 1.16. A port and frequency reconfigurable MIMO antenna for WLAN (a) bottom view (b) top view and (c) fabricated design [43]. ... 25 Fig. 1.17. Frequency agile integrated MIMO antenna (a) top view of simulated design (b) bottom view of simulated design (c) top view of fabricated design (d) bottom view of fabricated design [44]. ... 26 Fig. 2.1. Geometry and configuration of the UWB MIMO antenna in simulation (a) top view (b) bottom view (All dimension are in mm). ... 31 Fig. 2.2. (a) Surface current distribution without stub and with stub at 6 GHz; (b) Simulated S- parameter of the UWB MIMO antenna with and without stub. ... 31 Fig. 2.3. Effect of change in position of the via hole on its (a) reflection coefficient (b) coupling coefficient. ... 32 Fig. 2.4. Effect of change in width of thin metal strip on its (a) reflection coefficient (b) coupling coefficient. ... 33 Fig. 2.5. (a) Fabricated structure; (b) Simulated and measured S-parameter. ... 34 Fig. 2.6. Measured radiation pattern of the UWB MIMO antenna design in (a) E-Plane and (b) H-Plane. ... 35 Fig. 2.7. Simulated 3D-radiation pattern of the UWB MIMO antenna. ... 35 Fig. 2.8. Simulated radiation efficiency, measured peak gain and calculated ECC of the UWB MIMO antenna. ... 36 Fig. 2.9. Geometry and configuration of the UWB MIMO antenna in simulation (a) top view (b) bottom view (all dimension are in mm.). ... 39 Fig. 2.10. Effect of change in width of thin metal strip on its (a) reflection coefficient (b) coupling coefficient. ... 40 Fig. 2.11. Fabricated UWB MIMO antenna (a) top view (b) bottom view. ... 41 Fig. 2.12. Measured and simulated S-parameter of UWB MIMO antenna. ... 41 Fig. 2.13. Radiation pattern of UWB MIMO antenna in (a) YOZ-plane, (b) XOZ-plane and (c) XOY-plane. ... 42 Fig. 2.14. ECC of the proposed UWB MIMO antenna. ... 43 Fig. 2.15. Simulated total efficiency and gain of the proposed UWB MIMO antenna. ... 43

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Fig. 3.1. Single UWB antenna for MIMO configuration: (a) front side (b) back side and (c) front side with additional horizontal slot for notch at 5.5 GHz, and (d) its simulated S-parameter (All dimensions are in mm.). ... 49 Fig. 3.2. Effect of variation of slot length in the reflection coefficient of the UWB antenna. ... 50 Fig. 3.3. Surface current distribution of the single UWB MIMO antenna at 5.5 GHz: (a) without horizontal slot and (b) with horizontal slot. ... 50 Fig. 3.4. Fabricated structure of the initial UWB MIMO antenna (a) front side of the MIMO antenna (b) back side of the MIMO antenna. ... 51 Fig. 3.5. Zoomed view of the initial UWB MIMO antenna: (a) front side, (b) back side and (c) S- parameters. ... 52 Fig. 3.6. (a) Fabricated structure of the proposed UWB MIMO antenna with protruded ground plane and receded rectangular steps in ground plane (All dimensions are in mm.) (b) S- parameter of the proposed UWB MIMO antenna with high isolation... 54 Fig. 3.7. Surface current distribution of the initial and proposed UWB MIMO antenna (a) at 4.5 GHz and (b) at 10 GHz. ... 55 Fig. 3.8. Effect of common ground plane size variation on (a) reflection coefficient and (b) coupling coefficient. ... 56 Fig. 3.9. Radiation patterns of the UWB MIMO antenna in (a) YOZ-plane, (b) XOZ-plane and (c) XOY-plane. ... 57 Fig. 3.10. (a) Envelop correlation coefficient and (b) diversity gain of the UWB MIMO antenna.

... 58 Fig. 3.11. Total efficiency and gain of the proposed UWB MIMO antenna. ... 59 Fig. 3.12. (a) Single UWB antenna element ( All dimensions are in mm) (b) Chosen configuration of UWB MIMO antenna without common ground plane (CGP) (c) Comparison of simulated S-parameters. ... 62 Fig. 3.13. Configuration of UWB MIMO antenna for USB dongle application (a) with common ground plane (CGP) (b) with common and extended ground plane (C and EGP) (c) comparison of simulated S-parameters... 63 Fig. 3.14. Simulated UWB MIMO antenna with single band-notched characteristic (a) top view (b) bottom view and (c) simulated S-parameters. ... 66

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Fig. 3.15. Simulated UWB MIMO antenna with dual band-notch characteristic (a) top view (b) bottom view and (c) simulated S-parameters... 66 Fig. 3.16. Geometry of the proposed dual band-notched UWB MIMO antenna for USB dongle application (a) zoomed top view dimensions (b) zoomed bottom view dimensions (All dimensions are in mm). ... 67 Fig. 3.17. Simulated surface current distribution of the proposed dual band-notched UWB MIMO antenna for USB dongle application when (a) port-1 excited at 3.8 GHz (b) port-2 excited at 3.8 GHz (c) port-1 excited at 5 GHz and (d) port-2 excited at 5 GHz. ... 68 Fig. 3.18. Fabricated design of the proposed dual band-notched UWB MIMO antenna for USB dongle application (a) top view and (b) bottom view. ... 69 Fig. 3.19. Measured and simulated S-parameter of the proposed dual band-notched UWB MIMO antenna (a) port-1 and (b) port-2. ... 69 Fig. 3.20. Measured radiation patterns of the MIMO antenna in (a) XOZ, (b) YOZ and (c) XOY- planes at 3, 4.5, 6, 9 and 12 GHz. ... 71 Fig. 3.21. Simulated 3-D radiation patterns of the MIMO antenna at (a) 3 GHz, (b) 4.5 GHz, (c) 6 GHz, (d) 9 GHz and (e) 12 GHz when port-1 or port-2 are excited. ... 71 Fig. 3.22. Dual band-notched UWB MIMO antenna (a) calculated envelope correlation coefficient and simulated total efficiency (b) measured and simulated gain of antennas. ... 72 Fig. 3.23. Simulated structure of the antenna in different steps: (a) front side, (b) back side without OC stubs, (c) with OC stub at 3.3 GHz, (d) with OC stub at 5 GHz and (e) with OC stubs at both 3.3 and 5 GHz. ... 74 Fig. 3.24. Simulated S- parameter of the UWB antenna element. ... 75 Fig. 3.25. Geometry of the proposed dual band-notched UWB monopole antenna with its design parameters. ... 75 Fig. 3.26. Structure of dual band-notched UWB MIMO antenna (a) front side, (b) back side of initial configuration and (c) back side of initial configuration with common ground plane. (L= 36 mm). ... 76 Fig. 3.27. Comparison of S-parameter of dual band-notched UWB MIMO antenna with and without common ground plane (a) S11 and (b) S21. ... 77 Fig. 3.28. Geometry of the proposed dual band-notched UWB MIMO antenna (a) front side, (b) back side... 78

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Fig. 3.29. Comparison of S-parameter of the dual band-notched UWB MIMO antenna in its initial and final configuration (a) reflection coefficient (b) coupling coefficient. ... 78 Fig. 3.30. Comparison of surface current distribution at 6 GHz (a) initial structure and (b) final structure... 79 Fig. 3.31. Fabricated structure of the proposed dual band-notched UWB MIMO antenna (a) front side and (b) back side. ... 80 Fig. 3.32. Measured and simulated S-parameter of the proposed dual band- notched UWB MIMO antenna (a) reflection coefficient (b) coupling coefficient. ... 81 Fig. 3.33. Measured radiation pattern of the MIMO antenna in (a) XOY-plane, (b) XOZ-plane and (c) YOZ- plane. ... 81 Fig. 3.34. Envelope correlation coefficient of the UWB MIMO antenna. ... 83 Fig. 3.35. Simulated 3-D radiation pattern of the dual band-notched UWB MIMO antenna at 7 GHz, when (a) port 1 excited, (b) port 2 excited, (c) port 3 excited, (d) port 4 excited. ... 83 Fig. 3.36. Total efficiency and gain of the proposed UWB MIMO antenna. ... 84 Fig. 4.1. Simulated structure of the single UWB antenna with its S-parameter (a) front side (b) back side and (c) return-loss (All dimensions are in mm). ... 91 Fig. 4.2. Simulated 2×2 UWB MIMO antenna array configurations with its S-parameters (All dimensions are in mm.) (a) Initial UWB MIMO antenna array top and bottom view, (b) S- parameter of initial UWB MIMO antenna array elements, (c) Final UWB MIMO antenna array top and bottom view, (d) S-parameter of final UWB MIMO antenna array elements. ... 93 Fig. 4.3. Comparison of surface current distribution of initial and final UWB MIMO antenna configuration at 6 GHz (a) initial structure with port 1 excited, (b) final structure with port 1 excited, (c) initial structure with port 2 excited and (d) final structure with port 2 excited. ... 94 Fig. 4.4. Fabricated structure of the final UWB MIMO antenna configuration (a) front side and (b) back side. ... 95 Fig. 4.5. Measured and simulated S- parameter of the final UWB MIMO antenna (a) for element A1 and (b) for element A2. ... 95 Fig. 4.6. Fabricated design of 4×4 UWB MIMO antenna configuration (a) front side and (b) back side. ... 97

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Fig. 4.7. Measured and simulated S-parameter of the 44 UWB MIMO antenna configuration (a) return-loss, (b) coupling between orthogonal axis polarized elements and, (c) coupling between same axis polarized elements. ... 97 Fig. 4.8. Radiation pattern of the Antenna-1 and Antenna-2 in (a) XOZ-plane, (b) YOZ-plane, and (c) XOY-planes. ... 98 Fig. 4.9. (a) Simulated radiation efficiency and (b) measured peak gain of the UWB MIMO antenna design. ... 99 Fig. 4.10. ECC of the UWB MIMO antenna. ... 100 Fig. 4.11. (a) Geometry of the single UWB antenna; (b) S-parameter of UWB antenna element in each step; (c) Evolution steps of the structure of the UWB antenna element (All dimensions are in mm). ... 103 Fig. 4.12. Simulated four element array configuration (a) Initial configuration of the array with top view and bottom view (b) Final configuration of the array with top view and bottom view (c) Comparison of return loss (d) Comparison of coupling (All dimensions are in mm). ... 105 Fig. 4.13. Surface current distribution of the UWB MIMO antenna array configuration at 10 GHz (a) initial array with port 1 excited, (b) final array with port 1 excited. ... 106 Fig. 4.14. Fabricated structure of the proposed UWB MIMO antenna array with (a) top and bottom view (b) measured and simulated S- parameters. ... 107 Fig. 4.15. Effect of variation of spacing between antenna elements on coupling coefficient of same axis polarized elements. ... 108 Fig. 4.16. Measured radiation patterns of the antenna element A₁ in the array at (a) 3 GHz, (b) 6 GHz, (c) 9 GHz, (d) 12 GHz and (e) 15 GHz. ... 109 Fig. 4.17. Measured peak gain and simulated total efficiency of the UWB MIMO antenna array.

... 110 Fig. 4.18. (a) Group delay of UWB antenna; (b) Calculated ECC and CCL... 111 Fig. 4.19. Fabricated eight element UWB MIMO antenna array configuration (a) top view and bottom view, (b) measured return loss, (c) measured coupling between orthogonal axis polarized elements and (d) measured coupling between same axis polarized elements. ... 113 Fig. 5.1. Geometry of the proposed 3.5/5.5 GHz dual-band MIMO antenna (a) front view and (b) back view. ... 121 Fig. 5.2. MIMO antenna design in five stages. ... 121

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Fig. 5.3. Comparison of simulated S-parameter of the MIMO antenna in all the stages (a) S₁₁ and (b) S21. ... 123 Fig. 5.4. Comparison of simulated surface current distribution of the MIMO antenna without decoupling circuit (stage-II) and with decoupling circuit (stage-V). ... 125 Fig. 5.5. Fabricated structure of the 3.5/5.5 GHz dual-band MIMO antenna (a) front view and (b) back view. ... 126 Fig. 5.6. Comparison of simulated and measured S-parameters of the 3.5/5.5 GHz dual-band MIMO antenna. ... 126 Fig. 5.7. 2-D radiation pattern of the 3.5/5.5 GHz dual-band MIMO antenna in (a) XOZ-plane, (b) YOZ-plane and (c) XOY-plane. ... 127 Fig. 5.8. Geometry of the proposed dual-band MIMO antenna (All dimensions are in mm). ... 129 Fig. 5.9. Dual-band MIMO antenna configuration with front view and back view for all the states. ... 132 Fig. 5.10. Comparison of simulated S-parameter of dual-band MIMO antenna in all the states (a) reflection coefficient and (b) coupling coefficient. ... 133 Fig. 5.11. Comparison of simulated surface current distribution of dual-band MIMO Ant-II and Ant-III (proposed structure) at 2.4 GHz and 5 GHz. ... 133 Fig. 5.12. Effect of variation of parameter PM1on (a) reflection coefficient and (b) coupling coefficient. ... 135 Fig. 5.13. Effect of variation of parameter PM2 on (a) reflection coefficient and (b) coupling coefficient. ... 135 Fig. 5.14. Proposed dual-band MIMO antenna (a) fabricated structure and (b) comparison of measured and simulated S-parameter. ... 136 Fig. 5.15. Measured and simulated 2-D radiation patterns of the proposed dual-band MIMO antenna. ... 137 Fig. 5.16. Simulated 3-D radiation pattern of the proposed dual-band MIMO antenna when port- 1 and port-2 is excited at 2.4 GHz and 5 GHz. ... 138 Fig. 5.17. Calculated ECC, simulated total efficiency and peak gain of the proposed dual-band MIMO antenna. ... 139

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Fig. 6.1. Proposed dual-element dual-band MIMO antenna structures (a) top view of both configurations, (b) bottom view of the configuration-1 and (b) bottom view of the configuration- 2 (All dimensions are in mm). ... 147 Fig. 6.2. Design evolution of the proposed MIMO antenna in configuration-1 and configuration- 2... 148 Fig. 6.3. Simulated S-parameters of the MIMO antenna in different steps (a) S₁₁ for configuration-1, (b) S₂₁ for configuration-1, (c) S₁₁ for configuration-2 and (d) S₂₁ for configuration-2. ... 152 Fig. 6.4. Simulated current density of the proposed MIMO antenna in configuration-1 (a) at 2.4 GHz and (b) at 5 GHz. ... 152 Fig. 6.5. Critical design parameters of the proposed MIMO antenna (All parameters are in mm).

... 153 Fig. 6.6. Parametric analysis of critical geometric parameters of the proposed MIMO antenna in simulation (a) Variation in width of the decoupling circuit; (b) Variation in position of the via- hole; (c) Variation in diameter of the via-hole; (d) Variation in length of the J-shaped line; (e) Variation in the ground plane length; (f) Shift in position of the small ground plane; (g) Variation in height of the small ground plane; (h) Variation in feeding position of the feed line. ... 158 Fig. 6.7. Surface current distribution of dual-element dual-band MIMO antenna without (step-4) and with (step-6) decoupling circuit (a) for configuration-1 at 2.4 GHz and (b) for configuration- 2 at 3.5 GHz. ... 159 Fig. 6.8. Fabricated MIMO antenna designs (a) top view of configurations-1, (b) bottom view of configuration-1, (c) top view of configurations-2 and (d) bottom view of configuration-2. ... 161 Fig. 6.9. Measured and simulated S-parameters of the MIMO antenna designs (a) in configuration-1 and (b) in configuration-2. ... 162 Fig. 6.10. Optimized geometry of proposed frequency reconfigurable dual band MIMO antenna design (a) top view and (b) bottom view ... 163 Fig. 6.11. Schematic of the biasing circuit of PIN diode in series configuration. ... 164 Fig. 6.12. Equivalent lumped circuit model of a PIN diode MA4SPS402 in ON and OFF states.

... 165 Fig. 6.13. Fabricated Prototype of the proposed frequency reconfigurable dual-band MIMO antenna design (a) top view and (b) bottom view. ... 167

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Fig. 6.14. Zoomed view of the diode and its biasing circuit in both antenna elements of MIMO antenna. ... 167 Fig. 6.15. S-parameter of frequency reconfigurable dual-band MIMO antenna when diode D1 and D2 are (a) in ON-state and (b) in OFF-state. ... 168 Fig. 6.16. 2-D radiation patterns of the MIMO antenna (when D1 and D2 are ON) in lower band (at 2.4 GHz). ... 170 Fig. 6.17. 2-D radiation patterns of the MIMO antenna (when D1 and D2 are ON) at upper band (at 4.6 GHz, 5 GHz, and 5.5 GHz)... 170 Fig. 6.18. 2-D radiation patterns of the MIMO antenna (when D1 and D2 are OFF) in lower band (at 3.5 GHz). ... 171 Fig. 6.19. 2-D radiation patterns of the MIMO antenna (when D1 and D2 are OFF) in upper band (at 4.6 GHz, 5 GHz, and 5.5 GHz)... 171 Fig. 6.20. (a) Gain, (b) ECC and total efficiency of the frequency reconfigurable dual-band MIMO antenna when the diode is ON and OFF-state. ... 173

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LIST OF TABLES

Table 1-1 Comparison between low frequency and high frequency wireless systems ... 10

Table 2-1 Comparison table for UWB MIMO Antenna designs ... 37

Table 2-2 Comparison table for UWB MIMO Antenna for dongle applications ... 44

Table 3-1 Comparison table for single band notched UWB MIMO antenna designs ... 59

Table 3-2 Comparison table for dual band-notched UWB MIMO antenna designs ... 72

Table 3-3 Comparison table for dual band-notched UWB MIMO antenna designs ... 84

Table 4-1 Comparison of 2-element UWB MIMO antenna array designs ... 100

Table 4-2 Comparison of 4-element UWB MIMO antenna array designs ... 101

Table 4-3 State-of-the-art comparison of 4-element UWB MIMO Antenna Array designs ... 114

Table 4-4 State-of-the-art comparison of 8-element UWB MIMO Antenna Array designs ... 114

Table 5-1 Parameter of the proposed dual-band MIMO antenna ... 121

Table 5-2 Envelope correlation coefficient, total efficiency and gain of the dual band MIMO antenna ... 128

Table 5-3 Comparison table for 3.5/5.5 GHz MIMO antenna designs ... 128

Table 5-4 Comparison table for the 2.4/5 GHz MIMO antenna designs ... 140

Table 6-1 MIMO antenna states with diode states... 165

Table 6-2 Comparison of proposed dual-element dual-band MIMO antenna design with state-of- the-art designs ... 174