RECONFIGURABLE ELECTROMAGNETIC

BANDGAP STRUCTURES

LALITHENDRA KURRA

CENTRE FOR APPLIED RESEARCH IN ELECTRONICS

INDIAN INSTITUTE OF TECHNOLOGY DELHI

OCTOBER 2015

© Indian Institute of Technology Delhi (IITD), New Delhi, 2015

RECONFIGURABLE ELECTROMAGNETIC

BANDGAP STRUCTURES

by

LALITHENDRA KURRA

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

OCTOBER 2015

Dedicated

to

My Family

i

CERTIFICATE

This is to certify that the thesis entitled, “RECONFIGURABLE ELECTROMAGNETIC

BANDGAP STRUCTURES”, being submitted by Mr. Lalithendra Kurra 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, is a record of bonafide research work

carried out by him under our guidance and supervision.

Mr. Lalithendra Kurra has fulfilled the requirements for the submission of this thesis,

which to our knowledge has reached the requisite standard. The results contained in this

thesis have not been submitted in part or in full to any other university or institute for the

award of any degree or diploma.

(Dr. Shiban. K. Koul)

Professor

Centre for Applied Research in

Electronics

Indian Institute of Technology Delhi

Hauz Khas, New Delhi-110016, India

(Dr. Mahesh P. Abegaonkar)

Associate Professor

Centre for Applied Research in

Electronics

Indian Institute of Technology Delhi

Hauz Khas, New Delhi-110016, India

iii

ACKNOWLEDGEMENTS

I would like to take this opportunity to thank all those who have assisted me during my

research work in terms of technical support, moral support and friendship.

First, I am deeply indebted to Prof. Shiban. K. Koul and Dr. Mahesh P. Abegaonkar

for giving me an opportunity to work in this esteemed institution and agreeing to advise

me in the area of electromagnetic bandgap structures.

I would like to express my sincere gratitude to Prof. Shiban. K. Koul for his motivation

and support given to me throughout my research work. I also want to thank him for his

inspirational words related not only to the academics but also to philosophy of life.

I want to sincerely thank Dr. Mahesh P. Abegaonkar for his continuous encouragement,

discussions, support, suggestions and critical evaluation of the work at every stage of my

research work. Without his guidance, this thesis would not have taken this shape. His

vision laid a roadmap for my research work.

I want to give special thanks to Prof. Ananjan Basu for his support, inspiration and

critical advice given during my research work. I also thank Dr. Karun Rawat for his

advice and motivation towards my research goals. I thank Prof. Devi Chadda and Prof.

Sudhir Chandra, members of my research committee, for giving time and suggestions.

Their profound knowledge, professional ethics and generous attitude will surely benefit

rest of my career and my personal life.

I would like to thank Department of Science and Technology (DST) and National

Programme on Smart Materials and Systems (NPMASS) for providing some financial

support during my stay at IIT Delhi as a research scholar.

I would also like to thank my colleagues Mithlesh Kumar, Manoj Singh Parihar, Sandeep

Chaturvedi, Madhur Deo Upadhyay, Ritabrata Bhattacharya, Sukomal Dey, Sanjeev

Kumar, Srujana Kagita, Saurabh Pegwal, Ankita Katyal, Pooja Prakash, Rajesh Kumar

iv

Singh, Robin Kalyan, Deepika Sipal, Anushruti Jaiswal and Ayushi Barthwal for their

suggestions, moral support and friendly company. I also thank colleagues from other

laboratories, Monika, Lalat Indu Giri, Pradeep Rathod, and other research scholars of

CARE and M.Tech students of microwave group for their company during my research

work. Mr. Phaneendra Babu Bobba and Satish Babu Bhogineni, Ph. D. students from

electrical department also deserve thanks for their suggestion and company during my

stay in IIT Delhi. I would like to thank Mr. S. P. Chakraborty for his support and help

rendered during my research work. I would also like to thank Ashok Pramanik and

Pradeep Saxena for sharing their experience that helped me in my research work.

I would like to thank all the faculty and staff members of CARE who helped me in

various ways during my research work in CARE.

I thank IIT Delhi for providing accommodation for me and my family at IIT Delhi

campus. I would like to thank Phaneendra Babu's family for their support and

companionship to my family during their stay in IIT Delhi campus.

I would like to thank my parents, in-laws and other relatives for their continuous

encouragement, support and unconditional love. I am grateful to my father,

Satyanarayana, for his motivation which brought me to this level. I am also grateful to

my wife, Mrs. Harika for her patience, support, understanding, responsibilities she has

taken and for the sacrifices she has made during my course of research are priceless. I

would also like to value the presence of my 5 year son, Revanth Kumar, whose smiles

made me happy and the time I spend with him helped me in relaxation.

Finally, I thank Lord Venkateswara, for his blessings which has given me opportunity,

provided me strength, intellect and help through all the above mentioned persons that led

to successful completion of the thesis.

Lalithendra Kurra

v

ABSTRACT

The research work in this thesis is focussed on planar electromagnetic band gap

(EBG) structures, their characterization, applications and re-configurability. A planar

EBG structure is proposed using meander line inductors and interdigital capacitors. The

computed band gap of the proposed EBG structure is from 5.48-7.9 GHz, whereas the

band gap of the conventional EBG structure is from 9.41 to 12.41 GHz. Nearly 38%

reduction in the band gap centre frequency is achieved. Surface wave measurements

performed on 7 × 7 array of proposed EBG unit cells also confirms the band gap from

5.74-8 GHz band.

One dimensional array (1 × 7) of proposed EBG structure when loaded on either

side of a transmission line resulted in band stop/notch filter. The measured 3-dB

bandwidth of the band stop filter is from 4.95-5.37 GHz. The notch filter utilizing the

proposed EBG structure is cascaded to multiple-mode resonator (MMR) ultra-wideband

(UWB) filter to achieve a band-notched UWB filter. Single band-notched UWB filter

with notch centred around 5.16 GHz and dual band-notched UWB filter with notches

centred around 5.16 GHz and 8.24 GHz are achieved. Along with the filter, a band-

notched UWB antenna is also developed. Equivalent circuit of unit cell coupled to a

transmission line is developed and it is observed that the circuit simulated results

matched well with EM simulated results.

Re-configurability is achieved by connecting an additional section made of

interdigital lines (capacitor) to the unit cell using switches, which changes the effective

capacitance and hence the resonance frequency. Switchable filter is developed with 16

PIN diodes (MA4SPS402) connected in parallel and biased at 160 mA of total current in

the ON-state. In the ON-state, the measured 10-dB notch bandwidth is 0.344 GHz

centred around 5.095 GHz, and in the OFF-state, it is 0.316 GHz centred around 5.545

vi

GHz. A 450 MHz shift in frequency is observed by switching the diodes. By using

MA46H120 varactor diodes in the same circuit instead of PIN diodes, tunable notch filter

is achieved with notch band centre frequency tuned from 5.09 GHz to 5.43 GHz.

Equivalent circuit is developed for reconfigurable cell in the ON- and OFF-state.

Bandwidth reconfigurable band stop filter is developed using another

configuration of the unit EBG cell with a single meander line in parallel with a

interdigital capacitor. Using PIN diodes (MA4SPS402), the bandwidth of the notch is

varied. In the OFF-state, the 10-dB stop band is from 6.84 GHz to 7.47 GHz and in the

ON-state it is from 6.41 GHz to 7.33 GHz. 290 MHz increase in the bandwidth is seen in

the ON-state compared to the OFF-state.

By coupling EBG structure in broadside to the transmission line, a better band

stop filter is designed compared to the earlier edge coupled case. A multi-layered band-

pass filter (BPF) with suppressed harmonics is developed by broadside coupling three

unit cells in transverse direction to two open ended microstrip lines. The measured centre

frequency of the BPF is 2.56 GHz with 3-dB bandwidth of 0.38 GHz and harmonics are

below 20 dB up to 11 GHz. Diplexer is developed using the proposed BPF to mix 2.5

GHz signal from port 2 and 3.7 GHz signal from port 3 into port 1. The measured

isolation is better than 18 dB in the first pass band and in the second pass band it is better

than 26 dB. The harmonics are suppressed well below 10 dB up to 10 GHz.

Frequency selective surface property of the proposed structure (3.51 × 3.51 mm2)

is studied using CST Microwave Studio software which shows pass band characteristics

at 10.8 GHz. FSS screen formed by printing 13 × 13 array of unit is used as a superstrate

to a patch antenna operating at 10.8 GHz. The gain of the antenna is improved by 7 dB

with the FSS superstrate.

vii

TABLE OF CONTENTS

CERTIFICATE .................................................................................................................. i

ACKNOWLEDGEMENTs ............................................................................................ iii

ABSTRACT ....................................................................................................................... v

TABLE OF CONTENTS ................................................................................................ vii

LIST OF FIGURES ......................................................................................................... xi

LIST OF TABLES ......................................................................................................... xxi

1. INTRODUCTION ......................................................................................................... 1

1.1. Scope and Objective of the Work ............................................................................ 1

1.2. Organization of the Thesis ...................................................................................... 2

1.3. Electromagnetic Bandgap Structures ...................................................................... 4

1.3.1. Mushroom EBG Structure ............................................................................. 5

1.3.2. Uni-planar EBG Structure ............................................................................. 6

1.3.3. Properties of EBG Structures ........................................................................ 7

1.3.4. Compact EBG Structures .............................................................................. 8

1.3.5. Application of EBG Structures .................................................................... 12

1.3.6. Characterization of EBG Structures ............................................................ 19

1.3.6.1. Dispersion Diagram ..................................................................... 19

1.3.6.2. Surface Wave Measurement ........................................................ 22

1.3.6.3. Suspended Microstrip Method ..................................................... 24

1.3.6.4. Truncated Microstrip Line ........................................................... 24

viii

1.3.6.5. Reflection Phase Characteristics .................................................. 25

1.3.6.6. EBG Coupled Microstrip Line ..................................................... 26

1.3.7. Reconfigurable EBG Structures .................................................................. 27

1.3.8. Resonant-like EBG Structures .................................................................... 30

2. PROPOSED PLANAR EBG STRUCTURE ............................................................. 33

2.1. Introduction ........................................................................................................... 33

2.2. Proposed EBG Structure ....................................................................................... 33

2.3. Dispersion Diagram .............................................................................................. 35

2.4. Measurement Technique for Characterizing EBG Structure ................................ 37

2.5. EBG Loaded Transmission Line ........................................................................... 39

2.6. Equivalent Circuit Model ...................................................................................... 44

2.7. Conclusion ............................................................................................................ 61

3. APPLICATION OF EBG BAND STOP FILTER ................................................... 63

3.1. Introduction ........................................................................................................... 63

3.2. MMR UWB Filter ................................................................................................. 64

3.3. Band-Notched UWB Filter ................................................................................... 66

3.3.1. Single Band-Notched UWB Filter .............................................................. 66

3.3.2. Dual Band-Notched UWB Filter ................................................................. 72

3.4. Band-Notched UWB Antenna .............................................................................. 74

3.5. Conclusion ............................................................................................................ 80

ix

4. RECONFIGURABLE AND TUNABLE EBG STRUCTURES ............................. 81

4.1. Introduction ........................................................................................................... 81

4.2. Switchable Band-Notched UWB Filter ................................................................. 82

4.3. Tunable Notch Filter ............................................................................................. 89

4.4. Equivalent Circuit of Frequency Reconfigurable Unit Cell .................................. 91

4.5. Bandwidth Reconfigurable Band Stop Filter ........................................................ 93

4.6. Conclusion ............................................................................................................. 98

5. BAND PASS FILTER AND DIPLEXER ................................................................. 99

5.1. Introduction ........................................................................................................... 99

5.2. Band Stop Filter with Broadside Coupled EBG Cell ............................................ 99

5.3. Band Pass Filter (BPF) ........................................................................................ 105

5.4. Diplexer ............................................................................................................... 110

5.5. Conclusion ........................................................................................................... 116

6. FREQUENCY SELECTIVE SURFACE (FSS) APPLICATION ........................ 117

6.1. Introduction ......................................................................................................... 117

6.2. FSS Properties of the Proposed EBG Structure .................................................. 117

6.3. Application of FSS for Directivity Enhancement of the Patch Antenna ............. 121

6.3.1. Inset Feed Patch Antenna .......................................................................... 121

6.3.2. Patch Antenna with FSS as a Superstrate .................................................. 125

6.4. Conclusion ........................................................................................................... 134

x

7. CONCLUSION AND FUTURE SCOPE ................................................................ 135

7.1. Summary of the Thesis........................................................................................ 135

7.2. Future Scope of the Work ................................................................................... 137

REFERENCES .............................................................................................................. 139

APPENDIX - A .............................................................................................................. 155

APPENDIX - B .............................................................................................................. 163

PUBLICATIONS .......................................................................................................... 167

BRIEF BIO-DATA OF THE AUTHOR ..................................................................... 169

xi

LIST OF FIGURES

Fig. 1.1. Mushroom EBG structure (a) array and (b) cross-sectional view (origin of

capacitancce and inductance) [11], [12]. ..................................................................... 6

Fig. 1.2. 3×3 array of UC-PBG unit cells. .......................................................................... 7

Fig. 1.3. Spiral mushroom EBG structure [23]. ................................................................. 8

Fig. 1.4. Polar mushroom EBG structure [25]. ................................................................... 8

Fig. 1.5. Stacked mushroom EBG structure [12]. ............................................................... 9

Fig. 1.6. Mushroom EBG structure with intedigital lines [26]. .......................................... 9

Fig. 1.7. Fork-like EBG structure [27]. ............................................................................... 9

Fig. 1.8. Compact mushroom EBG structure with CSRR etched on the top metal plate

[29]. ........................................................................................................................... 10

Fig. 1.9. Compact planar EBG unit cell formed by distorting conventinal UC-EBG [30].

................................................................................................................................... 11

Fig. 1.10. Compact planar EBG cell with triangular plates and peripheral traces [31]. ... 11

Fig. 1.11. Schematic of two unit cells of compact planar EBG structure [32]. ................ 11

Fig. 1.12. Compact EBG unit cell [33]. ............................................................................ 11

Fig. 1.13. EBG unit cell with meander lines and inter-digital capacitors [34].................. 12

Fig. 1.14. Spiral capacitor and meander inductor (SC-ML) planar EBG structure [35]. .. 12

Fig. 1.15. Rabbet spiral dual-band EBG structure [40]. .................................................... 12

Fig. 1.16. Cross-sectional view of patch antenna surrounded by mushroom EBG structure

[11]. ........................................................................................................................... 13

Fig. 1.17. Top view of patch antenna surrounded by conventional UC-EBG structure

[14]. ........................................................................................................................... 13

Fig. 1.18. Array antenna with mushroom EBG for mutual coupling reduction [43]. ....... 14

Fig. 1.19. Array antenna with UC-EBG for mutual coupling reduction[45]. ................... 14

xii

Fig. 1.20. TEM-waveguide with UC-PBG structure [50]. ................................................ 15

Fig. 1.21. LPF on UC-PBG ground plane. (a) Schematic diagram. (b) Results [51]. ...... 15

Fig. 1.22. Parallel coupled microstrip BPF with UC-PBG ground plane. (a) Schematic

diagram. (b) Results compared with the conventional BPF [13]. ............................. 16

Fig. 1.23. Comparison of transmission in CB-CPW, CB-CPW with PBG ground plane

and CPW [54]. .......................................................................................................... 16

Fig. 1.24. Horizontal wire antenna over (a) conducting flat metal plate, (b) high

impedance ground plane (c) and return loss versus frequency characteristics [11]. 17

Fig. 1.25. Schematic diagram of slot antenna backed with UC-PBG [57], [58]. ............. 18

Fig. 1.26. Unit cell of UC-EBG structure showing irreducible Brillouin zone [14]......... 20

Fig. 1.27. Simulation set up for dispersion diagram. ........................................................ 20

Fig. 1.28. Dispersion diagram of UC-PBG structure with 25 mil substrate. (a) Computed.

(b) Reported [14]....................................................................................................... 22

Fig. 1.29. Dispersion diagram of UC-PBG structure with 50 mil substrate. (a) Computed

(b) Reported [14]....................................................................................................... 22

Fig. 1.30. TM surface wave measurement set up [12]. ..................................................... 23

Fig. 1.31. TE surface wave measurement set up [12]. ...................................................... 23

Fig. 1.32. Method of suspended microstrip [27]. .............................................................. 24

Fig. 1.33. Transmission through UC-PBG lattice by truncated microstrip line. (a) Top

view. (b) Transmission characteristics. [14]. ............................................................ 24

Fig. 1.34. Reflection phase measurement set up [11], [12]. ............................................. 25

Fig. 1.35. Reflection phase of a two-layer high-impedance surface [11], [12]. ............... 25

Fig. 1.36. Mushroom EBG structure coupled to microstrip transmsision line [69].......... 26

Fig. 1.37. Band-notched UWB filter using IDCLLR structure [77]. ................................ 26

Fig. 1.38. Reconfigurable fork-like EBG unit cell [27]. ................................................... 28

xiii

Fig. 1.39. Short-circuited hairpin resonator. (a) Schematic diagram of unit cell. (b) Cells

loaded to a transmission line. (c) Result of reconfiguraable filter [88], [89]. ........... 29

Fig. 1.40. UWB filter with tunable notch based on folded SIR [75]. ............................... 30

Fig. 1.41. Reconfigurable frequency band-notched ultra-wideband (UWB) antenna using

SRR [90]. ................................................................................................................... 30

Fig. 1.42. Anisotropic UC-PBG etched on ground plane of microstrip line [93]. ............ 32

Fig. 2.1. Proposed planar EBG unit cell. ........................................................................... 34

Fig. 2.2. Conventional planar EBG unit cell. .................................................................... 34

Fig. 2.3. Dispersion diagram of the proposed EBG structure. .......................................... 35

Fig. 2.4. Dispersion diagram of the conventional planar EBG structure. ......................... 36

Fig. 2.5. Dispersion diagram of the proposed EBG strcucture along Γ-X-M-Y-Γ

irreducible brillouin square. ...................................................................................... 36

Fig. 2.6. Dispersion diagram of the proposed EBG structure drawn for the entire

structure. .................................................................................................................... 37

Fig. 2.7. Photogragh of fabricated array of 77 proposed EBG cells. .............................. 38

Fig. 2.8. Measured results of TE and TM surface waves in the proposed EBG structure.

................................................................................................................................... 39

Fig. 2.9. EBG structure coupled to a microstrip line. (a) Schematic diagram. (b)

Photograph of fabricated circuit. (c) Simulated and measured results. ..................... 40

Fig. 2.10. Surface current plot of EBG loaded transmission line (a) at 6.1 GHz in

passband and (b) at 5.25 GHz in stopband. ............................................................... 41

Fig. 2.11. Unit cell of structure 'B'. (All dimensions are in mm.) ..................................... 42

Fig. 2.12. Simulated results of various proposed structures loading a transmsion line. ... 42

Fig. 2.13. Simulated results of the proposed EBG structure loading a tranmision line for

various values of d. ................................................................................................... 43

xiv

Fig. 2.14. Simulated results comparing the proposed structure (Fig. 2.1) and conventional

structure (Fig. 2.2) loading a transmission line......................................................... 44

Fig. 2.15. Single unit cell coupled to a microstrip transmission line. ............................... 45

Fig. 2.16. Meander line inductor. (a) Metal pattern. (b) Equivalent circuit model. .......... 46

Fig. 2.17. Magnetic flux lines. (a) Positive mutual inductance. (b) Negative mutual

inductance. ................................................................................................................ 47

Fig. 2.18. Parallel strips with complete overlap................................................................ 47

Fig. 2.19. Parallel strips overlapped with unequal strip lengths. ...................................... 48

Fig. 2.20. Parallel strips partially overlapped with unequal strip lengths. ........................ 48

Fig. 2.21. Parallel strips without overlap. ......................................................................... 49

Fig. 2.22. Symmetrical coupled microstrip lines. (a) Odd-mode capacitance. (b) Even

mode capacitance. ..................................................................................................... 50

Fig. 2.23. Intedigital capacitor. (a) Metal pattern. (b) Equivalent circuit. ........................ 54

Fig. 2.24. Asymmetric coupled microstrip transmission line. ......................................... 55

Fig. 2.25. Coupling capacitance between transmission line and the unit cell. ................. 58

Fig. 2.26. Equivalent circuit of a single unit cell coupled to a transmission line. ............ 58

Fig. 2.27. Comparison of circuit and EM simulated results of a single cell coupled to a

transmission line. ...................................................................................................... 59

Fig. 2.28. Band stop filter. (a) Equivalent circuit. (b) Comparison of circuit and EM

simulated results........................................................................................................ 60

Fig. 3.1. MMR weakly coupled to 50 Ω transmission lines. (All dimensions are in mm.)

................................................................................................................................... 64

Fig. 3.2. Resonant frequencies of MMR. .......................................................................... 64

Fig. 3.3. MMR UWB filter. (a) Schematic diagram. (b) Photograph. (c) Measured and

simulated results........................................................................................................ 66

xv

Fig. 3.4. Band-notched UWB filter with EBG coupled to output line (Filter A). (a)

Photograph. (b) Measured results. (c) Comparison of measured and simulated

results. ....................................................................................................................... 68

Fig. 3.5. Simulated results of band-notched UWB filter with electric and open add space

boundary conditions. ................................................................................................. 69

Fig. 3.6. Band-notched UWB filter with EBG structure coupled to input and output lines

(Filter B). (a) Photograph. (b) Measured and simulated results. ............................... 70

Fig. 3.7. Band-notched UWB filter with EBG structure coupled to input line, output line

and low impedance line of the filter (Filter C). (a) Photograph. (b) Measured and

simulated results. ....................................................................................................... 71

Fig. 3.8. Unit cell sized to 3.65 mm × 3.65 mm................................................................ 72

Fig. 3.9. Dual band-notched UWB filter (Filter D). (a) Photograph. (b) Measured results.

................................................................................................................................... 73

Fig. 3.10. Schematic diagram of the band-notched UWB antenna. (a) Front View. (b)

Back View. (a=44.45, b=20.55, s=0.1, d=1, g=0.06, L=4.95, r=7.86 and all

dimensions are in mm). ............................................................................................. 75

Fig. 3.11. Photograph of the band-notched UWB antenna. (a) Front view. (b) Back view.

................................................................................................................................... 75

Fig. 3.12. Measured and simulated |S11| of the band-notched UWB antenna. .................. 76

Fig. 3.13. E-plane pattern (y-z plane - φ=90) of the band-notched UWB antenna. (a)

Simulated. (b) Measured. .......................................................................................... 77

Fig. 3.14. H-plane pattern (x-z plane - φ=0) of the band-notched UWB antenna. (a)

Simulated. (b) Measured. .......................................................................................... 78

Fig. 3.15. Gain of the UWB antenna and the band-notched UWB antenna. .................... 79

xvi

Fig. 3.16. Surface current in the band-notched UWB antenna at (a) 5.2 GHz and (b) 8

GHz. .......................................................................................................................... 80

Fig. 4.1. Schematic diagram of metal pattern of the reconfigurable EBG. (All dimensions

in mm.) ...................................................................................................................... 82

Fig. 4.2. Switchable band-notched UWB filter implemented with diodes. (a) Photograph.

(b) Zoomed view showing band stop filter with various elements. .......................... 83

Fig. 4.3. Photograph of the switchable band-notched UWB filter. (a) Ideal ON-state. (b)

Ideal OFF-state.......................................................................................................... 84

Fig. 4.4. Simulated and measured results of the switchable band-notched UWB filter. (a)

Ideal ON-state. (b) Ideal OFF-state. ......................................................................... 86

Fig. 4.5. Simulated results with over-etching, without over-etching and measured results

of the switchable band-notched UWB filter in the ideal ON-state. .......................... 86

Fig. 4.6. Simulated results of switchable band-notched UWB filter in CST and ADS. (a)

ON-state. (b) OFF-state. ........................................................................................... 88

Fig. 4.7. Measured results of the switchable band-notched UWB filter with diodes in the

ON-state and OFF-states. .......................................................................................... 89

Fig. 4.8. Comparison of measured and ADS simulated results of the switchable band-

notched UWB filter implemented with diodes. ........................................................ 89

Fig. 4.9. Measured results of the tunable notch filter with varactor diode in reverse bias.

................................................................................................................................... 90

Fig. 4.10. Variation of frequency and bandwidth of the tunable filter with bias voltage of

varactor diode............................................................................................................ 90

Fig. 4.11. Reconfigurable EBG unit cell coupled to a transmission line. ......................... 91

Fig. 4.12. Equivalent circuit of the reconfigurable EBG unit cell coupled to a

transmission line. ...................................................................................................... 92

xvii

Fig. 4.13. Comparison of circuit simulated and EM simulated results of the

reconfigurable unit cell coupled to a transmission line. ............................................ 93

Fig. 4.14. Two unit cells connected by a switch ............................................................... 94

Fig. 4.15. Photograph of the fabricated bandwidth reconfigurable band stop filter and its

zoomed view showing various elements. .................................................................. 95

Fig. 4.16. Photograph of the ground plane of the bandwidth reconfigurable band stop

filter (Fig. 4.15). ........................................................................................................ 95

Fig. 4.17. ADS simulated results of the bandwidth reconfigurable filter with diode in the

ON- and OFF-states. ................................................................................................. 96

Fig. 4.18. Measured results of the bandwidth reconfigurable filter with diode in the ON-

state, diode OFF-states and simple microstrip line. .................................................. 97

Fig. 5.1. Electric field diagram of a microstrip transmission line. .................................. 100

Fig. 5.2. Electric field diagram of a broadside and edge coupling of the EBG to a

microstrip transmission line. ................................................................................... 100

Fig. 5.3. Cross-sectional view of multilayer broadside coupled EBG band stop filter. .. 101

Fig. 5.4. Broadside coupled EBG band stop filter with 3 EBG cells placed longitudinally.

................................................................................................................................. 101

Fig. 5.5. Simulated results of the broadside coupled EBG band stop filter with variations

in number of cells in the longitudinal direction. ..................................................... 102

Fig. 5.6. Broadside coupled EBG band stop filter with 3 EBG cells placed transverse to

the line. .................................................................................................................... 103

Fig. 5.7. Simulated results of the broadside coupled EBG band stop filter with variations

in number of cells in the transverse direction. ........................................................ 103

Fig. 5.8. Surface current plots of a broadside-coupled EBG bandstop filter with 3-EBG

cells in transverse-direction at (a) 2.832 GHz (b) 4.94 GHz and (c) 5.76 GHz. ..... 104

xviii

Fig. 5.9. Comparision of edge coupled and broadside coupled EBG band stop filter. ... 105

Fig. 5.10. (a) Cross sectional view of the BPF. (b) Photograph of fabricated top and

middle layer of the BPF, printed on either sides of 0.127 mm thick substrate. (All

dimensions are in mm.) ........................................................................................... 106

Fig. 5.11. Transmission characteristics of the BPF with variations in J values. ............ 107

Fig. 5.12. Simulated S11 of the BPF with J=11 mm. ...................................................... 108

Fig. 5.13. Measured and simulated results of the proposed BPF and the reference filter.

................................................................................................................................. 109

Fig. 5.14. BPF with five cells. (a) Photograph of top and middle layers. (b) Measured and

simuated results. ...................................................................................................... 110

Fig. 5.15. Photograph of fabricated top layer and middle layer of the diplexer, printed on

either sides of 0.127 mm substrate. (All dimensions are in mm.) .......................... 111

Fig. 5.16. Surface current in diplexer at (a) 2.5 GHz and (b) 3.7 GHz. .......................... 113

Fig. 5.17. Measured and simulated results of the diplexer. ............................................ 113

Fig. 5.18. Diplexer measurement setup. ......................................................................... 114

Fig. 5.19. Measured results of the diplexer on spectrum analyzer. (a) Insertion loss. (b)

Isolation................................................................................................................... 115

Fig. 6.1. Unit cell (structure 'A'). (All dimensions are in mm.) ...................................... 118

Fig. 6.2. Simulation set up using CST Microwave Studio.............................................. 118

Fig. 6.3. Simulated results of unit cell (Fig. 6.1) with the simulation setup of Fig. 6.2. 119

Fig. 6.4 FSS measured results. ........................................................................................ 119

Fig. 6.5. Unit cell. (a) Structure 'B'. (b) Structure 'C'. (All dimensions are in mm.) ...... 120

Fig. 6.6. FSS characteristics of different unit cells. ........................................................ 121

Fig. 6.7. Schematic diagram of patch antenna. ............................................................... 124

Fig. 6.8. Simulated and measured |S11| of the patch antenna. ......................................... 124

xix

Fig. 6.9. Simulated and measured radiation pattern at 10.8 GHz of the patch antenna. (a)

E-plane (y-z plane - φ=90). (b) H-plane (x-z plane - φ=0). ................................. 125

Fig. 6.10. Patch antenna with FSS screen as superstrate. ............................................... 126

Fig. 6.11. Reflection coefficient of the patch antenna with and without FSS superstrate.

................................................................................................................................. 127

Fig. 6.12. Simulated radiation pattern at 10.8 GHz of the patch antenna with FSS

superstrate with variations in d. (a) E-plane pattern (y-z plane - φ=90). (b) H-plane

pattern (x-z plane - φ=0). ....................................................................................... 128

Fig. 6.13. Measured and simulated radiation pattern at 10.8 GHz of the patch antenna

with FSS superstrate. (a) E-plane pattern (y-z plane - φ=90). (b) H-plane pattern (x-z

plane - φ=0). .......................................................................................................... 129

Fig. 6.14. Measured radiation pattern at 10.8 GHz of the patch antenna with and without

FSS superstrate. (a) E-plane pattern (y-z plane - φ=90). (b) H-plane pattern (x-z

plane - φ=0). .......................................................................................................... 130

Fig. 6.15. Simulated radiation pattern of the patch antenna, patch antenna with dielctric

superstrate and patch antenna with FSS superstrate operating at 10.8 GHz. (a) E-

plane pattern (y-z plane - φ=90). (b) H-plane pattern (x-z plane - φ=0).............. 131

Fig. 6.16. Power flow top view of (a) patch antenna (b) patch antenna with dielectric

superstrae and (c) patch antenna with FSS superstrate. .......................................... 132

Fig. 6.17. Measured radiation pattern of the patch antenna, with and without FSS

superstrate operating at 6.7 GHz. (a) E-plane pattern (y-z plane - φ=90). (b) H-

plane pattern (x-z plane - φ=0). ............................................................................. 133

xxi

LIST OF TABLES

Table 2.1. Summary of results of various proposed structures loading a transmsion line.

................................................................................................................................... 43

Table 3.1. Summary of characteristics of band-notched UWB filters. ............................. 74

Table 6.1. Comparison table of FSS showing improvement in the antenna directivity. . 134