BANDWIDTH IMPROVEMENT AND SIZE REDUCTION OF MICROSTRIP PATCH ANTENNA USING HFFS A thesis Submitted to the Council of Faculty of Science and Science Education School of Science at the University of Sulaimani in partial fulfillment of the requirements for the degree of Master of Science in Physics
By
Dana Saeed Muhammad B.Sc. in physics (2007), University of Sulaimani
Supervised by
Dr. Asaad Mubdir Jasim Assistant Professor
Pushpar, 2714
June, 2014
حتسني عرض احلزمة الرتددية وتقليل احلجم هلوائي الرقعة الدقيقة بأستخدامHFSS رسالة مقدمة اىل جملس فاكليت العلوم و تربية العلوم سكول العلوم يف جامعة السليمانية كجزء من متطلبات نيل شهادة ماجستري علوم يف الفيزياء
من قبل
دانا سعيد حممد بكالوريوس فيزياء ) ، ( 2007جامعة السليمانية ِباشراف
د.اسعد مبدر جاسم استاذ مساعد
حزيران4102 ,
0241
رمضان,
باشكردنى فراوانى باندةكةى و بضوككردنةوةى قةبارةى ئاريَلى ضةسثيَنةرى تويَذالَ تةنك بة بةكارهيَنانى HFSS نامةيةكة ثيَشكةش كراوة بة ئةجنومةنى فاكةلَتى زانست و ثةروةردة زانستةكان سكولَى زانست لة زانكؤي سليمانى وةك بةشيَك لة ثيَداويستيةكانى بةدةستهيَنانى برِوانامةى ماستةرى زانست لة فيزيا
لة اليةن
دانا سعيد حممد
بةكالريؤس لة فيزيا ( ,)7002زانكؤى سليمانى
بةسةرثةرشتى
د.أسعد مبدر جاسم
ثرؤفيسؤري ياريدةدةر
حوزيران7002 , 7202
ثوشثةرِ,
ثوختة لةم ماستةر نامةيةدا ,زؤر رِيَطا بةكارهيَنراوة بؤ طةورةكرنى فراوانى باندى لةرينةوةى ئاريَلى ضةسثيَنةرى تويَذالَ تةنك .نارِيَكى لة ثيَكهاتةى زةمينى ) (DGSئاريَلى ضةسثيَنةرى تويَذالَ تةنكى ضوارطؤشة ,سيَطؤشة/الكيَشة و بازنةى ثيَشنياركران بؤ فراوانكردنى بةرطرى باندى لةرينةوةةكةى. ) (DGSثيَكهاتووة لة كةمكردنةوةى دريَذي زةمينيةكةى وة دروستطرنى ضةندقلَشيَكى شيَوة جياواز لة ليَواري رِووتةختى زةمينيةكةدا .واماندانبو لةم كارةدا كاريطةريةكانى ئةو ) (DGSكة ثشكنني و ضاكسازى بوَ ئاريالةكة كرا بة بةكارهيَنانى بةرنامةى .HFSS ئةو ئةجنام انةى كة دةستمانكةوت ثيشانياندا بةكةمكردنةوةى دريَذى زةمينيةكة ) (DGSو دروستكردنى سىَ ,يةك و سىَ قلَش لة ضةند شويَنيَكى جياوازى زةمينيةكة ,دةركةوت فراوانى لةرينةوةى زؤر بةهيَزمان ئةداتيَ(بة نسبةت لةرةلةرى ناوةرِاست) بؤ )44411-3413( %431طيَطا هيَرتز )41443-3433( %411 ,طيَطا هيَرتز وة )44443-3434( %434طيَطا هيَرتز بوَ هةريةكة لة ضةسثيَنةرى ضوارطؤشة ,سيَطؤشة/الكيَشة و بازنةى يةك لة دوايةك .وة هةروةها كةمكردنةوةى قةبارةى ئاريَلى تويَذالَ تةنكى ضوارطؤشة ,سيَطؤشة/الكيَشة و بازنةى بة رِيَذةى %8321 ,%83,1و %8321لة لةرةلةرى زرنطانةوةى 12.4طيَطا هيَرتز 1214 ,طيَطا هيَرتز و 12.1طيَطا هيَرتز يةك لةدواى يةك .بة بةراورد كردن بةو ئاريَالنةى هةمان ثيَكهاتةى ئةندازةييان هةية وة هةمان لةرةلةر زرنطانةوةى ئيشطردنيان هةية بةبيَ ).(DGS لة بةشى كؤتاى ئةم كارةدا زياتر وردبونةوة لة كاريطةرى خويَندنةوةى مادة نةطةيةنةرى كارةباى ناواخنةكة لةسةر فراوانى باندى لةرينةوةى ئاريَلةكة .واماندانا سيَ جؤرى جياواز لة مادةى
نةطةيةنةرى كارةباى بة ناوةكانى (Duroid) :كة نةطؤرِى نةطةياندنةكةى ( FR-epoxy , )323كة نةطؤرِى نةطةياندنةكةى ( )121و Rogers TMM10كة نةطؤرِى نةطةياندنةكةى ( .)423لة ئةجنامدا ثيشاندرا كة لةرةلةرى زرنطانةوةكة اليداوة بةرةو نرخيَكى كةم بة زيادبونى نةكةياندنى كارةباى وة لة هةمان كاتدا فراوانى لةرينةوةى باندةكةش كةمى كردووةز
ACKNOWLEDGMENTS
I would like to start by thanking ALLAH, without His graciousness the completion of this work would not have been possible. Allah the Almighty has entrusted me with the abilities and provided me with the courage to complete a long journey. I would like to thank my supervisor, Dr. Asaad M. Jasim, for his continuous encouragement, invaluable supervision, timely suggestions and inspired guidance throughout the completion of this thesis. Special mention must be made of my mother A. Xder. I would also like to acknowledge the financial support received through a studentship award by the Faculty of Science and Science Education for two years that enabled me to undertake this research project.
I would like also to thank the Department of Physics at the Faculty of Science and Science Education, especially science committee and head of the department, Asst. Prof. Dr. D. Abdulla. My great appreciation and gratefulness are to my friends Mr.H. Abdulla, Mr.R. Taib., Mr.F. Arif, Mr.R. Muhammad, Mr.S. Muhammad., Mr.A. Ahmed and Mr.P. Abdulkareem, they sent to me some special papers. In particular, I would like to thank the dean of Erbil Technology Institute, Asst. Prof. Dr.S. Osman. I cannot forget Miss.C. Hussien for her moral support and availability during the thesis. I also thank my friends Dr.S. Abubakr and Mr.S. Hussien for guidance during the writing.
Finally, I must express my sincere gratitude to my wife, Sara. She knows more than anyone else about the sacrifices that had to be made, and I extend my gratitude to one and all who are directly or indirectly involved in the successful completion of this thesis.
Dana vi
ABSTRACT
In this thesis, many techniques of bandwidth enhancement for microstrip antennas are reviewed. The defected ground structure DGS for square, triangular/rectangular and circular microstrip patch antennas are suggested to broaden the impedance bandwidth. The DGS includes reduction in ground length, and making different notch shapes at the edge of the ground plane. The effects of the proposed DGS in the present thesis on antenna performance are investigated using high frequency structure simulator HFSS.
The obtained results indicate that the DGS of length reduction with three, one and three notches at difference location of the ground gives an enhancement of bandwidth percentage (relative to center frequency) of 134% (3.42-17.45)GHz, 145% (2.33-14.63)GHz and 131% (3.31-16.13)GHz for square, triangular/rectangular and circular patches respectively. Also a size reduction of 83.5%, 82.5% and 83.5% achieved for square, triangular/rectangular and circular patches at resonance frequency of 4.06GHz, 4.49GHz and 4.05GHz, respectively, compared with the antennas having the same geometrical structure and operating at the same resonance frequencies but without DGS.
The final part of this work has concentrated on studying the effect relative dielectric permittivity of substrate on the antenna bandwidth. Three different dielectric substrates namely: Duroid of with
, FR-epoxy with
and Rogers TMM10 with
are considered. The results indicate that the resonance frequency is shifted towards the lower values with increasing the relative permittivity and the antenna bandwidth reduces.
vii
CONTENTS Acknowledgements………………….….…….………………………………..
VI
Abstract…………………………………………...…………………..….…….
VII
Table of Contents……..…………………………………..……………...…….
VIII
List of Figures………………………………………………………………….
XI
List of Tables……………………………...……..……..…..…….....................
XV
Glossary…………...…………………………….….……………...…………..
XVII
List of Abbreviations …………...………...………………………..……….…
XX
Chapter 1: Introduction 1.1 Significance and Structure of Microstrip Antenna.
1
1.2 Thesis Organization……………………....…………...………………...……….. 3 1.3 Characteristics and Application of Microstrip Antennas………………………...
3
1.3.1 Advantages of Microstrip Antennas………….……………………………. 4 1.3.2 Disadvantages……………………………………………………………… 4 1.3.3 Applications of Microstrip Antenna...………….……………...…………... 5 1.4 Feeding Method ……………………………...……...…………………...……… 6 1.5 Analysis Techniques for Microstrip Patch Antenna………………………...…...
10
1.5.1 Transmission Line Model…………........…...…………………….……..… 10 1.5.2 The Finite-Element Method……...………………….………………….….
13
1.6 Thesis Objectives………………………………………………………………...
16
1.7 Literature survey…………………………………………………………………
17
Chapter 2: Designs and Analysis OF BROADBAND MICROSTRIP ANTENNA. 2.1 Introduction to Patch Antenna………….………………………………..………. 23 2.2 Defected Ground Structure (DGS)………………………………………………. 24 viii
2.3Antenna Substrate Material……………..…………………………………..……. 27 2.4 Antenna Analysis and Performance…...…………………………………...…….
28
2.4.1 Return Loss………………………………………………………………...
28
2.4.2 Voltage Standing Wave Ratio (VSWR) ……………………………...…… 29 2.4.3 Bandwidth………………………………………………………………….
30
2.4.4 Directivity and Gain………………………………………………………..
32
2.4.5 Radiation Pattern……………………………………………………………...…… 33
2.5 High Frequency Structure Simulator (HFSS) ………………………………...…
35
2.6 Antenna Test by HFSS Software………………………………………………...
38
Chapter 3: Results and Discussion 3.1 Introduction………………………..…….…………………………………….....
43
3.2 Design and Performance of Square Microstrip Patch Antenna……….…………. 43 3.2.1 Design and Performance of SMSP Antenna with DGS………………...….
46
3.2.2 SMSP Antenna with DGS and Notches……………………………………
51
3.3 Triangular/Rectangular Microstrip Patch Antenna………………………………
58
3.3.1 Design and Performance of T/RMSP Antenna with DGS..………………..
60
3.3.2 T/RMSP antenna design and performance with DGS and Notches……….. 61 3.4 Design and Performance of Circular Patch Without DG……..…………………
65
3.4.1 Optimization of Patch Radius……………………………………………...
66
3.4.2 Design and Performance of circular patch with DGS……………………...
68
3.4.3 Design and Performance of CMSP Antenna with DGS and Notches…...… 69 3.5 Effect of Substrate Relative Permittivity on Antenna Bandwidth……………….
74
3.6 General Results and Discussion………………………………………………….
76
3.6.1 Bandwidth Comparisons for Different Patch Shapes………………………….. 76 3.6.2 Antenna Size Reduction………………………………………………………..
77
3.6.3 Relationship of Resonance Frequencies with and Without DGS……………… 79
ix
Chapter 4: Conclusions and Future Suggestions 41 Conclusions…………………………………………………………………....…
81
4.2Future Work………...………………………………………………………..…...
82
References ……...…………………………………………………………………… 83
x
List of Figures Figure No.
Figure Title
Page no.
1.1
Microstrip patch antenna structure ………………..........…... 2
1.2
Shapes of microstrip patch antennas ……………...…....…… 2
1.3
Microstrip line feed ………..………………………….…...... 7
1.4
Coax cable (probe) feeding of microstrip patch antenna …… 8
1.5
Aperture feeding of microstrip patch antenna ………….…...
8
1.6
Proximity-coupling feed ……………..………………….......
9
1.7
Patch structure according to TL model ……………………..
11
1.8 1.9 2.1
Physical and Effective Length of Rectangular Microstrip Antenna……………………………………………………… 12 Full-Wave EM Analysis in the FEM ………………………..
14
Geometry of studied antenna patches (a) Square (b) Triangular / Rectangular (c) Circular patches……………………...
24
2.2
Reducing the length of the ground plane ……..………….....
25
2.3
Reducing the width of the ground plane………....…..….......
25
2.4
Making a notch at the center of the ground plane edge…......
26
2.5
Making a notch at the right of the ground plane edge……....
26
2.7
Making a combination of a above notches………….……....
27
2.6
Making a notch at the left of the ground plane edge………
27
2.8
Bandwidth of MSPA ……………………………………….. 31
2.9
Radiation pattern of dipole antenna…………………………
34
2.10
HFSS windows displays…………………………………….
35
2.11
Create the dimensions of the MSPA by HFSS……………...
36
2.12
Check the validation of the MSPA for errors……………….
36
2.13
The output windows of HFSS software……………………..
36
2.14
Finite element mesh of MSPA………………………………
37
xi
2.15
(a) The actual MSP antenna, (b) The designed MSP antenna by HFSS software…………………………………………...
38
2.16
Return loss of actual antenna by HFSS……………………... 39
2.17
Gain of actual antenna by HFSS……………………………. 39
2.18
Fabricated MSPA with partially ground plane……………...
40
3.1
Structure of square microstrip patch antenna (MSPA)……...
42
3.2
Variation of S11 versus frequency of normal SMSPA………
43
3.3
3.3 3D Polar plot of SMSP antenna: (a)Gain (b)Directivity without DGS at 14.26 GHz…………………………………. 44
3.4
2D Radiation pattern of SMSP antenna at 14.26GHz…….… 44
3.5
Defect ground structure (DGS) of SMSP antenna………….. 45
3.6
3.7
3.8
Variation of SMSP antenna Return loss versus frequency operation with DGS of (Lg=20mm.)………………………... Variation of SMSP antenna Return loss versus frequency operation with DGS of (Lg=12mm.)………………………...
45 46
Variation of SMSP antenna Return loss versus frequency operation with DGS of (Lg=10.5mm.)………………………
47
3.9
Variation of SMSP antenna Return loss versus frequency operation with DGS of (Lg=8mm.)………………………….
48
3.10
Variation of SMSP antenna Return loss versus frequency operation without DGS and with various DGS cases……...
48
3.11
3.12
3.13
3.14
3.15
Square patch (a) Defect ground plane (DGS) with center notch, (b) Patch with DGS and center notch………………. 50 Characteristics of SMSP antenna return loss at center notch with Difference Dimensions………………………………. Characteristics of
50
versus Frequency for SMSP antenna
with DGS and with different notches cases…………………
52
Current distrbution on the DGS at one, two and three notches………………………………………………………
53
Polar plot (a) Gain and, (b) Directivity of SMSP antenna with DGS ant 3notches……………………………………... xii
54
3.16
E & H Plane pattern at resonance frequency 4.06GHz……... 54
3.17
VSWR versus frequency of the proposed antenna structure..
3.18
3.19
3.20
3.21
3.22
3.23
3.24
3.25
55
Surface current distributions on SMSP antenna with DGS and 3notches………………………………………………… 55 Triangular/Rectangular patch shape, (a) Current distribution, (b) Normal patch………………………………. 56 Characteristics of Return Loss versus frequency for TMSP antenna accommodated with rectangular Patch…………….. 57 Characteristics of Return Loss versus frequency of T/RMSP antenna at Lp=9mm Without DGS…………………………
58
Return losses versus frequencies curves at difference ground plane length…………………………………………………. 59 Characteristics of
versus Frequency for T/RMSP
antenna with DGS and with different notches cases………... 60 VSWR of T/RMSP antennas with DGS and 1notch at 4.49 GHz………………………………………………………….
61
2D Radiation pattern of T/RMSP antenna with DGS and 1notch at 4.49 GHz………………………………………….
62
3D plot, (a) Gain, (b) Directivity of T/RMSP antenna 3.26
3.27 3.28
3.29
without DGS. (c) Gain and (d) Directivity of T/RMSP antenna with DGS and 1 notch at resonance frequency 4.49 GHz………………………………………………………….
63
Structure of circular microstrip patch CMSP antenna………
64
Characteristics of return loss versus frequency CMSP antenna without modifications………………………………
64
Characteristics of return loss versus frequency for CMSP antennas with various radiuses and with DGS (Lg=10.5mm). 65
3.30
Variations of CMSP antenna return loss versus frequency without DGS and with various DGS cases………………….
3.31
Structure of CMSP antennas with DGS and notches……….. 68
3.32
Characteristics of
versus Frequency for CMSP antenna xiii
66
with DGS and with different notches cases………………… 3.33 3.34 3.35 3.36 3.37 3.38
69
Surface current distributions on CMSP antenna……………. 70 3D Polar plot of CMSP for Antenna Gain at resonance frequency 4.05 GHz…………………………………………
70
3D Polar plot of CMSP for antenna directivity at resonance 71 frequency 4.05 GHz………………………………………… 2D Radiation pattern of CMSP antenna for E-plane and Hplane at resonance frequency 4.05 GHz…………………….
71
VSWR of CMSP antennas with DGS and 3notches………... 72 Characteristics of S11 versus frequency for SMSP antenna and with various substrate material relative permittivities….
73
3.39
Comparision between the variation of S11 versus frequency for optimum results of square, triangular/rectangular and circular patches……………………………………………...
3.40
S11of SMSP antennas without DGS (Length Reduction) for antenna No.1,No.2 and No.3………………………………... 76
3.41
74
S11 versus frequency of SMSP antennas with DGS (Length Reduction) for antenna No.1, No.2 and No.3……………….
xiv
76
LIST OF TABLES Table No.
Table Title
1.1
Characteristics of difference feeding techniques……………………
9
2.1
Characteristics of proposed materials.….............…...……………… ….............................
28
3.1
Dimensions of proposed square patch antenna……………………...
42 112-114
3.2
Parameters of proposed SMSPA…………………………………….
43
3.3
SMSP antenna parameters with DGS of Lg=20mm…………………
45
3.4
SMSP antenna parameters with DGS of Lg=12mm…………………
3.5
SMSP antenna parameters with DGS of Lg=10.5mm……………….
46 116-118 47
3.6
SMSP antenna parameters with DGS of Lg=8mm………………….. 48
3.7
Page No.
Comparisons between the SMSP antenna parameters for different DGS cases and without DGS………………………………………..
49
3.8
SMSP Antenna parameters with GDS and center notch…………….
51
3.9
Dimensions of notches in defect ground structure of SMSP………..
52
3.10
Parameters of SMSP antenna antennas. DGS cases and without DGS. with DGS and with different notch cases…………………………………………………………………
52
3.11
Dimensions of proposed triangular/rectangular microstrip patch (T/RMSP) Antenna………………………………………………….
3.12
57
Comparisons between the T/RMSP antenna parameters for different patch lengths………………………………………………………… 57
3.13
Characteristics of T/RMSP antenna at Lp=9mm Without DGS…….. 58
3.14
Parameters of T/RMSP antenna at different ground plane length…..
59
3.15
DGS with Notch Dimensions of T/RMSP Antennas………………..
60
3.16
Parameters of T/RMSP antenna with DGS and with different notch.
61
3.17
Parameters of CMSP antennas with various radius and with DGS cases. (Lg=10.5mm)………………………………………………………..
3.18
65
Comparisons between the CMSP antenna parameters for different DGS cases…………………………………………………………...
67
3.19
CMSP antennas with different notch cases…………………………..
68
3.20
Parameters of CMSP antenna with DGS and with different notch….
69
cases.
xv
3.21
Resonance frequencies, substrate permittivity, BW and S11 of SMSP antenna with different materials……………………………... 73
3.22
Comparisons between the square, triangular/rectangular and circular MSPA Parameters with DGS and notches for optimum…… 75
3.23 3.24
Size reduction of MSP antennas at difference patch shapes………... results. Frequency shift in
77
for different patch shapes with and without
DGS…………………………………………………………………. 78
xvi
Glossary Q
Quality Factor
Wp
Patch Width
Lp
Patch Length
εreff
Effective Dielectric Constant
ΔL
Frings factor
Leff
Effective Length
S-parameters
Scattering Parameters
Wg
Width of Ground
Lg
Length of Ground
H
High of Substrate
Wf
Width of Feed Line
Lf
Length of Feed Line
3D
Three Dimensions
D
Directivity
G
Gain
fr
Resonance Frequency
fc
Center Frequency
GHz
Giga Hertz
C
Speed of Light High Level Frequency Low Level Frequency Width of Notch Length of Notch Width of Right Notch Length of Right Notch Width of Left Notch Length of Left Notch
xvii
1N
One Notch
2N
Two Notches
3N
Three Notches Width of Feed Line Length of Feed Line Free-Space Wavelength Relative Permittivity Permittivity of Free space Relative Permeability Permeability of Free space
T
Patch thickness Guided Wavelength Is the Wave Vector in Vacuum
m, n, p
Integer Number of Modes Permittivity of Free space Permeability of Free space Reflection Coefficient Antenna Impedance Characteristic Impedance of the Transmission Line
Vmax
Amplitude of Maximum Voltage
Vmin
Amplitude of Minimum Voltage Is the Incident Voltage Is the Reflection Voltage
Γ
Reflection Coefficient Omnidirectional Radiation Average Intensity Overall Direction
U
Radiation Intensity in a given Direction Maximum Radiation Intensity Total Power Radiation by Antenna Radiation Efficiency xviii
Reflect Power Total Power Total Input Power RL
Return Loss Angular Frequency
G
Antenna Gain
D
Antenna Directivity
EV
Vertical Electric Component
EH
Horizontal Electric Component
RL
Return Loss
xix
ABBREVIATIONS
BW
Bandwidth Bandwidth with Respect to Center Frequency Bandwidth with Respect to Resonance Frequency
CMSP
Circular Microstrip Patch
CP
Circular Polarization
CST
Microwave Studio
dB
Decibel
dBi
Decibel-isotropic
DGS
Defect Ground Structure
EM
Electromagnetic waves
FDTD
Finite Difference Time Domain
FEM
Finite Element Method
GHz
Giga Hertz
GSM
Global System for Mobil
HFSS
High Frequency Structure Simulator
IEEE
Institute of Electrical and Electronics Engineers
MOM
Methods of Moments
MHz
Mega Hertz
MSPA
Microstrip Patch Antenna
MSP
Microstrip Patch
PDF
Partial Differential Equation
Radar
Radio Detection and Ranging
RF
Radio Frequency
RL
Return Loss
RMPA
Rectangular Microstrip Patch Antenna
SMSP
Square Microstrip Patch
xx
TEM
Transverse Electromagnetic waves
T/RMSP
Triangular/Rectangular Microstrip Patch Transfers Magnetic Modes
tanδ
Loss Tangent of Dielectric
UWB
Ultra Wide Band
VSWR
Voltage Standing Wave Ratio
WiFi
Wireless Fidelity
WIMAX
Worldwide Interoperability for Microwave Access
WLAN
Wireless Local Area Network The dominant mode of circular microstrip patch antenna.
3G
Three Generator
2D
Two Dimensions
3D
Three Dimensions
xxi
الخالصة
تحسين عرض الحزمة الترددية وتقليل الحجم لهوائي الرقعة الدقيقة بأستخدامHFSS في هذه األطروحة تتم دراسة التقنيا ت الخاصة بتعريض الحزمة الترددية لهوائيات الرقعة الدقيقة. وتقترح األطروحة ان يكون لهوائي الرقعة الدقيقة ذو الشكل المربع،المثلث والدائري ارضيا مشوه التركيب Defected Ground Structure DGSلغرض تعريض الحزمة الترددية الممانعية.
يتضمن أألرضي المشوه التركيب تقليل في طوله وعرضه وكذلك عمل حزوز مختلفة األشكال على حافة مستواه .ويتم في األطروحة ايضا بحث تأثيرات أألرضي المشوه التركيب على أداء الهوائي ومحاكاتها بأستخدام محاكي ذو التركيب التردد العالي. HFSS تشير النتائج المستحصلة بأن هوائي الرقعة الدقيقة ذات الشكل المربع ،المثلث/المستطيل والدائري والذي له ارضي مشوه التركيب(تقليل في طوله مع وجود ثالثة حزوز ،وجود حز واحد ووجود ثالثة حزوز على التوالي) يعطي نسبة تعريض بالحزمة الترددية وقدرها (3.42- 134% ) (2.33-14.63GHz) 145% ، 17.45GHzو (3.31-16.13GHz) 131%وعلى التوالي ايضا .كما تحقق تقليل في حجم الهوائي بنسبة 83.5%للشكل المربع وبنسبة 94.6%للشكل المثلث/المستطيل وبنسبة 83.5%للشكل الدائري وعند التردد الرنيني 4.49GHz ، 4.06GHz و 4.05GHzعلى التوالي مقارنة بحجوم هوائيات لها نفس الشكل وتعمل بنفس الترددات الرنينية ولكن بدون استخدام تركيب األرضي المشوه.
ويتركزالجزء األخير من هذا البحث دراسة تأثير سماحية القاعدة العازلة للهوائي على عرض الحزمة الترددية .تفترض الدراسة ثالث مواد عازلة وهي Duroid :ذات ثابت عزل FR- ، 2.2 epoxyذات ثابت عزل 4.4و Rogers TMM10ذات ثابت عزل . 2.2تشير النتائج المستحصلة بأن زيادة ثابت عزل قاعدة الهوائي تؤدي الى ازاحة تردد الرنين الى قيمة اقل من األولى وكما تؤدي الى تقليل في عرض الحزمة الترددية.
CHAPTER ONE
INTRODUCTION
CHAPTER ONE
INTRODUCTION
1.1 Significance and Structure of Microstrip Antenna Nowadays, mobile communication plays an important role in our civilization and becomes part of our daily life, and new wireless communication methods and services have been enthusiastically adopted by people throughout the world. The evolution of modern wireless communication systems has increased dramatically the demand for antennas, capable to be embedded in portable, or not, devices which serve a wireless land mobile or terrestrial-satellite network. In the modern wireless world, the need for smaller, broadband and reliable antennas has been fully demonstrated in current advancements in communication industry and significant growth in wireless communication market and consumer demand [1-2].
Microstrip patch antennas are widely used in wireless communications due to their inherent advantages of low profile, less weight, and low cost, together with the ease of integration with microstrip circuits. Moreover, they are easily integrated into arrays or into microwave printed circuits. So, they are attractive choices for the above mentioned types of applications. Therefore, microstrip antennas are the most rapidly developing field in the last twenty years [3].
Microstrip patch antennas were first introduced by Munson in early 1970s and became popular primarily for space-borne applications. Microstrip antenna is widely considered to be suitable for many wireless applications, even though it usually has a narrow bandwidth. Microstrip patch antenna consists of a radiating patch on one side of a dielectric substrate, which has a ground plane on other side, as shown in (Fig. 1.1). The patch is generally
1
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INTRODUCTION
made of conducting material such as copper or gold and can take any possible shape. The radiating patch and the feed lines are usually photo etched on the dielectric substrate [4-5].
Figure 1.1: Microstrip patch antenna structure [5].
The microstrip patch antenna is usually designed as a broadside radiator (its pattern maximum is normal to the patch). This can be achieved by choosing the proper way to excitation under the patch. The radiating patch shape may be square, rectangular, thin strip (dipole), circular, elliptical, or any other configuration as shown in (Figs. 1.2). However, rectangular patches are more common. Other configurations are complex to analyze and require heavy numerical computations [6].
Figures 1.2: Shapes of microstrip patch antennas.
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The basic design considerations for rectangular patch, the length (L) of the patch is usually
, where
is the operating free-space wavelength. The
patch is selected to be very thin such that
(where t is the patch thickness). The high
(h) of dielectric substrate is usually is typically in the range
. The dielectric constant [4-5].
1.2 Thesis Organization The thesis is organized as follows:
chapter one presents introduction to microstrip patch antenna with advantages and disadvantages, feeding techniques, simulation methods and literature survey relate to broadband antenna.
chapter two includes the methodology and description of the proposed antennas that verify the aims of the thesis.
chapter three presents the obtained results and discussion.
chapter four includes the conclusion and future works.
1.3 Characteristics and Application of Microstrip Antennas
The microstrip antenna has proved to be an excellent radiator for many applications because of its several advantages, but it also has some disadvantages. The advantages, disadvantages and applications of the Microstrip Antenna MSA are given in the following sections:
3
CHAPTER ONE
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1.3.1 Advantages of Microstrip Antennas
Microstrip antennas have several advantages compared to conventional microwave antennas, and therefore many applications cover the broad frequency range from ~100 MHz to ~ 100GHz[1]. The advantage are:
Light weight, low volume, thin profile configuration which easily conforms to the surface of the product or vehicle.
Low cost, easy amenability to mass production, easy integration with microwave integrated circuits.
Capability to produce linear and circular polarization with broadside radiation patterns.
They can be made compact for use in personal mobile communication devices.
They allow for dual and triple frequency operations.
1.3.2 Disadvantages On the other side, there are also some limitations compared to the conventional antennas as follows [7]:
Low efficiency.
Low power.
Poor polarization purity, poor scan performance.
Very narrow frequency bandwidth, which is typically only a fraction of a percent or at most a few percent.
Low gain about (~6dB.). 4
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Excitation of surface waves.
Microstrip patch antennas have a very high antenna quality factor (Q). Q represents the losses associated with the antenna and large Q leads to narrow bandwidth and low efficiency. However Q can be reduced by increasing the thickness of the dielectric substrate. But as the thickness increases, an increasing fraction of the power is absorbed in the substrate and leads to lower radiation efficiency and evolution of surface wave which degrades the radiation. This surface wave contribution can be counted as an unwanted power loss since it is ultimately scattered at the dielectric bends which causes degradation of the characteristics. However, surface waves can be minimized by the use of photonic band gap structures. Other problems such as lower gain and lower power handling capacity can be overcome by using an array configuration for the elements [8-9].
1.3.3 Applications of Microstrip Antenna
Microstrip patch antennas represent a superior selection for standard mobile services and satellite communication systems due to attractive characteristics of small size, low cost and weight, conformability, and ease of manufacturing; that is why these antennas have been developed in the last decades increasingly. The practical applications for mobile systems are in portable or pocket-size equipment and in vehicles [10].
Laptop wireless communication systems have developed rapidly in the recent years. In addition to having omnidirectional radiation and internal fabrication, the antennas designed for these portable products must be small and have a low profile to fit in with a limited space, especially, laptop computers usually retain a small space at their edge for an antenna . The printed-circuit antennas use technology simply because they are considered to be made simple and cheap [11].
Low bandwidth and slow data transmission speed of Global Position System GSM technology is sufficient for normal calls, whereas 3G technology is used in cases where high data transmission rates and bandwidth are required such as video calling, video messaging (video sending and sharing applications). Thus, the frequency bands are used 5
CHAPTER ONE
INTRODUCTION
more efficiently. In some applications where an increased bandwidth is needed, dual frequency patch antenna is one of the alternative solutions. When modern communication systems, such as satellite, radar and GSM require operation at wide bandwidth, wide bandwidth patch antennas may avoid the use of two different antennas [12-13].
Some notable system applications for which microstrip antennas have been developed include the following fields:
Satellite communication;
Doppler and other radars;
Radio altimeter;
Command and control systems;
Missiles and telemetry (stick-on sensor and weapon fusing);
Remote sensing and environmental instrumentation;
Feed elements in complex antennas;
Satellite navigation receivers;
Biomedical radiator;
Mobile radio;
Integrated antennas;
Global Position Systems (GPS).
1.4 Feeding Methods There are several basic methods for microstrip antenna feeding. These methods can be classified in two categories- contacting and non contacting. In the contacting method the RF power is fed directly to the radiating patch using a connecter, they are microstrip feed (Fig. 1.3) and coax feed (Fig. 1.4). In Non-contacting method, electromagnetic coupling is done to transfer the power between the feed line and the radiating patch, they are Aperture coupling feed (Fig. 1.5) and proximity coupling feed (Fig. 1.6) [14].
The feeding techniques are required in order to match the characteristic impedance of the feed line to that of the patch antenna. When the characteristic impedance of the antenna 6
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is the same as the feed line, the antenna is said to be matched to the line. If the antenna is not matched, maximum power transfer will not take place. In general, however, the impedance of the antenna is not the same as that of the feed line. The antenna can be matched depending on the design impedance. Here in this work, a the patch is selected because the standard characteristic impedance is
input impedance of .
In the present work, the microstrip line feed is chosen for the proposed antenna designs because it is considered the simplest way to feed a microstrip patch and to connect a microstrip line directly to the edge of the patch. Thus, the feed line can be etched on the same substrate to provide a planar structure. The (Tab 1.1) below summarizes the characteristics of the different feed techniques for patch antennas [14-15].
Figure 1.3: Microstrip line feed [14].
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Figure 1.4: Coaxial cable (probe) feeding of microstrip patch antenna [14].
Figure 1.5: Aperture feeding of microstrip patch antenna [14].
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Figure 1.6: Proximity-coupling feed [14].
Table 1.1: Characteristics of difference feeding techniques[15]. characteristics
Microstrip
Coax Feed
Line Feed Spurious feed
Aperture
Proximity
Coupling
Coupling
Feed
Feed
More
More
Less
Minimum
Better
Poor due
Good
Good
Alignment
Alignment
required
required
radiation Reliability
to soldering Ease of
Easy
fabrication
Soldering and drilling needed
Impedance
Easy
Easy
Easy
Easy
2-5%
2-5%
2-5%
13%
Matching Bandwidth(achiev ed with impedance matching)
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1.5 Analysis Techniques for Microstrip Patch Antenna
There are a number of methods that can be used to analyze patch antennas. Most of these methods fall into one of two broad categories: approximate methods and full wave methods.
The approximate methods are based on simplifying assumptions and therefore they have a number of limitations and are usually less accurate but the computation time is usually very small. These groups consist of transmission line model and cavity model, which are based on equivalent magnetic current distribution around the patch edges [16].
The second groups (full-wave methods) consist of method of moment's (MoM), finiteelement method (FEM) and finite-difference time domain (FDTD), which are based on the electric current distribution on the patch conductor and the ground plane [17]. These methods include all relevant wave mechanisms and rely heavily upon the use of efficient numerical techniques. Therefore, they tend to be much more complex than the approximate methods and also provide less physical insight. Very often they also require vast computational recourses and extensive solution times. In the followings sections, transmission line model (approximate method) is presented to simply understand the mechanism of patch radiation, and the finite-element method (FEM) (full-wave models) is also introduced because the analysis of the present work based on this method [16].
1.5.1 Transmission Line Model
The transmission line model is the simplest model used for analyzing rectangular microstrip antennas. It was indicated earlier that the transmission-line model is the easiest of all but it yields the least accurate results and it lacks versatility. The transmission line model represents the microstrip antenna by two slots of width (W) and height (h), separated by a low-impedance
transmission line of length (L).
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The microstrip is essentially a non-homogeneous line of two dielectrics, typically the substrate and air. Hence, as seen in (Fig. 1.7), most of the electric field lines reside in the substrate and parts of some lines in air. As a result, this transmission line cannot support pure transverse-electromagnetic (TEM) mode of transmission, since the phase velocities would be different in the air and the substrate. Instead, the dominant mode of propagation would be the quasi-TEM mode [18-19].
Fields at the edge of the patch, both for the length and the width, undergo fringing as a result of the finite dimension of the patch. Besides the dimensions, height and dielectric constant of the substrate also affect the amount of fringing. Because of fringing, patch looks wider than its physical dimensions. In order to take into account this effect, an effective dielectric constant
is calculated. To study the theory of microstrip
transmission line, we have two different cases:
(Narrow strip line) and this is not what we are interested in.
The second case
and
(wider transmission line). (1.1)
Where W is the patch width (slot length), h is the height of substrate (slot width) and is the dielectric constant of substrate. The value of
is slightly less than
because
the fringing fields around the periphery of the patch are not confined in the dielectric substrate but are also spread in the air.
Patch
Radiating slot Substrate Figure 1.7: Patch structure according to TL model [19].
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INTRODUCTION
The amount of fringing is the function of the dimensions of the patch and the high of the substrate. However transmission line models are limited to rectangular geometries and cannot predict cross polarization radiation and surface wave effects. The electric field radiated from a microstrip antenna provides a boundary between two different dielectrics: air and the substrate material. Due to the slight distortion of the field at the boundary, the patch may appear longer in an electrical sense. This is illustrated in (Fig. 1.8) [15].
(a)Top view of antenna.
(b) Side view of antenna.
Figure 1.8: Physical and effective length of rectangular microstrip antenna [15].
The patch is viewed as a transmission line resonator with no transverse field variation, i.e., the field only varies along the length, and the radiation occurs from the fringing fields, which are viewed as open circuits at the ends of the transmission line.
The fringing fields are accounted for by the distance
, which is a function of the
effective dielectric constant. The electric length of the patch is given by:
(1.2)
is the effective length and,
is extension length of the patch. The extension in
length maybe calculated by:
(1.3)
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INTRODUCTION
It is already known that the effective length of the patch is equal to (
, so for a given resonance frequency
, the effective length
can be calculated by [18]:
(1.4) Where, c=velocity of light in free space=
Along the width of the patch, the voltage is maximum and the current is minimum due to the open ends. The field at the edges can be resolved in to normal and tangential components with respect to the ground plane. It is seen in (Fig. 1.8) that the normal components of the electric field at the two edges along the width are in opposite directions, thus out of phase since the patch is
long and hence they cancel each other in the
broadside direction. The tangential component in (Fig. 1.8b), which are in phase, means that the resulting fields combine to give maximum radiation field normal to the surface of the structure. Hence the edges along the width can be represented as two radiating slots, which are
apart and excited in phase and radiating in the half space above the ground
plane [15].
1.5.2 The Finite-Element Method
The Finite Element Method (FEM) is a very versatile technique because it allows the analysis of complex structures. It has been used in a wide variety of problems like modeling waveguides and transmission lines, cavities, etc. It is also computationally efficient because it yields sparse matrices [20].
The Finite Element Method (FEM) frequency domain based on full-wave computational technique is used for antenna structure optimal design and performance simulation. A fullwave computational technique provides a complete solution to Maxwell's equations within the computational space for all conductors and materials. In contrast, the FEM allows for arbitrary specification of the material within the volume, which is an inherent advantage of FEM over numerical methods. FEM is a very powerful tool for solving complex 13
CHAPTER ONE
INTRODUCTION
engineering problems, the mathematical formulation of which is not only challenging but also tedious [21].
It was introduced to the electromagnetic community towards the end of the 1960's. Since then, a great progress has been made in terms of its application to electromagnetic problems. In addition, the FEM is a well-known frequency-domain technique which is highly capable of modeling 3D complex structures within homogeneities. Typical fullwave EM analyzes in the FEM is shown in (Fig. 1.9) [20,22].
Figure 1.9: Full-wave EM analysis in the FEM [20].
When using the FEM for electromagnetic problems, the electric field is the unknown variable that has to be solved for, the method is implemented by discrediting the entire volume over which the electric field exists, together with its bounding surface, into small elements. In which triangular elements are used for surface meshes and tetrahedron elements for volumetric meshes. Simple linear or higher-order functions on the nodes, along the edge or on faces of the elements, are to model the electric field. For antenna problems, the volume over which the electric field exists will have one boundary on the antenna and another boundary some distance away from the antenna [22].
The latter boundary is an absorbing boundary, which is needed to truncate the volume. One view point from which the FEM can be derived is that of variation analyze. The method starts with the partial differential equation (PDE) from Maxwell's equations and finds a variation functional from which the minimum (or external point) corresponds with the solution of the PDE, subject to the boundary conditions. An example of such a functional is the energy functional, which is an expression describing all the energy associated with the configuration being analysis, in terms of the electric field. After the 14
CHAPTER ONE
INTRODUCTION
boundary conditions have been enforced, a matrix equation is obtained. This equation can then be solved to yield the amplitudes that are associated with the functions on the elements used to model the electric field. The matrix associated with the FEM is a sparse matrix due to the fact that every element only interacts with the elements in its own neighborhood. Other parameters, such as the magnetic field, induced currents and power loss, can be obtained from the electric field. The major advantage of the FEM is that the electrical and geometrical properties of each element can be defined independently. Therefore, very complicated geometries and in homogenous materials can be treated with relative ease. This implies that the analysis of microstrip antennas with finite ground plane and layers is also possible [22].
In this work, the MSPA have been simulated by using the software Ansoft-HFSS based on Finite Element Method (FEM). The simulation technique was used to calculate the three dimensional electromagnetic fields inside a structure. The principle of this method is to divide the study area into many small regions (tetrahedrons), then calculating the local electromagnetic field in each element. The local fields
are calculated in each
tetrahedron elements from the following equations [23].
(1.5)
(1.6)
and
are respectively the permittivity and permeability of materials.
is the wave vector in vacuum.
is the pulsation angular
frequency [57].
To validate the proposed structure, Ansoft High Frequency Structure Simulator (HFSS) was used to simulate the performance of the antenna. The commercial EM software version HFSS 13 is used for simulation and optimization. HFSS automatically generates field solutions, port characteristics, and s-parameters. It is able to quickly calculate antenna metrics such as gain, directivity, far-field pattern cuts, far field 3D plots, and 3dB
15
CHAPTER ONE
INTRODUCTION
beamwidth. The main advantage of the FEM is that, because the volume is discredited in tetrahedral, the shape of the antenna can be more accurately represented [24-25].
1.6 Thesis Objectives
The thesis is aims to:
1- To improve the impedance bandwidth by using difference patch shapes( Square, Triangular/Rectangular and Circular) antenna and chose suitable material has lower a dielectric constant. By increasing the Bandwidth more data can be carried out, on the other side high Q-factor gives better directivity hence more gain for that here a trade off is required between Bandwidth and Q-factor (quality factor).
2- Several factors affecting the bandwidth of the microstrip antenna such as the thickness of the substrate, the dielectric constant of the substrate, the shape of the patch and Defect Ground Structure (DGS) would be studied in this work. Propose broadband antenna structures with
changing the following parameters:
a) Microstrip patch shapes (square, triangular/rectangular and circular) b) Ground plane shape (different length, with notches) c) Substrate material.
3) analysis the proposed structures using HFSS simulator and study the effects of above parameters on antenna performance including : impedance-bandwidth, VSWR, directivity, gain and radiation pattern of the studied antennas.
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CHAPTER ONE
INTRODUCTION
1.7 Literature survey
One limiting factor in the performance of microstrip patch antennas is the narrow impedance bandwidth (a few percent). Enhancement of the impedance bandwidth of microstrip elements is a challenge to the researchers. Various techniques have been developed during the last three decades. Still a significant fraction of researchers is involved in this area resulting in new techniques which are almost in their infancy. Several designs for small-size wide-bandwidth microstrip antennas are examined through simulation and experiments.
It is interesting to note that one of the first attempts to enhance the impedance bandwidth, stacking patches was proposed in the late 1970s, however, the method was unsuccessful in the feeding procedures (which are often referred to as direct contact feeding techniques) [26]. The broader operating bandwidth (BW) has been proposed by I. J. Bahl, in 1980 and realized by cutting the slots of either half wave or quarter wave in length [27] to improve the bandwidth.
In a 1983, symposium paper, Dean Paschen [28] showed how filter theory could be used to expand the impedance bandwidth of microstrip antennas up to 35%. Lo and his group attacked the problem of extending the bandwidth of circularly polarized radiation from a patch antenna at the 1984 Symposium.
Girisi with partner ,1985,[29] proposed a new technique to increase BW. Three new configurations for increasing the impedance bandwidth of the microstrip patch antennas are described. In these configurations, additional resonators are directly coupled through short sections of microstrip line to the radiating edges, non radiating edges, and all the four edges of the rectangular patch antennas, respectively. Green’s function approach and segmentation method are used for the analysis. The experimental results are in reasonable agreement with the analysis and impedance bandwidths of 548 MHz (18%), 605 MHz (19%), and 810 MHz (24%) are obtained for these three configurations, respectively in Sband (substrate thickness = 0.318 cm and
, = 2.55).
17
CHAPTER ONE
INTRODUCTION
In 1986 Aanandan et al. [30] proposed a new designing consist of some layers of substrate and some patches to improve bandwidth. This antenna has a resonant frequency of 844 MHz and a 2:1 VSWR bandwidth of 6%. Thus the parasitic microstrip antenna gives a bandwidth eight times more than that of the corresponding planar antenna.
In 1987, Robert with partner [31] proposed more than a new design. A broadband, contiguous stacked, two-layer, square microstrip patch antenna element design is described which can be used for linear or circular polarization. Experimental investigations resulted in bandwidths up to 26% of the center frequency
.
In 1989, Sorbello et al. suggested a number of novel circularly polarized slot radiating elements have been developed and incorporated into high efficiency broadband arrays they are built and tested at Ku-band. In all cases, efficiencies of greater than 50% have been a new technique to increase bandwidth; broad-band impedance matching was proposed as a natural solution to increase the bandwidth. The maximum obtainable bandwidth was calculated using Fano’s broadband matching theory. By this technique,
they could
increase the the bandwidth (BW) to 275MHz (9.1%).
In 1990, Japanese researchers [32] have proposed another method to increase BW of microstrip patch antenna, the method was the microstrip antenna composed of three elements: the radiating element, first parasitic element (matching element) to widen the BW of impedance (10% at resonance frequency 7.5 GHz.) and second parasitic element (director) to increase the gain.
In 1991, David et al. [33] has investigated a wideband patch antenna composed of two triangular patches using an EM simulation program. The antenna bandwidth is twice as large as that of an ordinary rectangular patch of the same size (before splitting).
In 1993, Yang et al. [34] has used another technique to increase the BW; a method for increasing its bandwidth is to change the single tuned resonance into a double tuned resonance. This may be achieved by using a larger coupling aperture. The factors which affect the bandwidth of the aperture coupled microstrip antenna and then present two other means for increasing its bandwidth: using a slotted patch and multi-slot coupling.
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CHAPTER ONE
INTRODUCTION
In 1995, Sunil's paper [35] proposed a new patch shape of confocal annular elliptic patch has been. It is printed on a substrate having permittivity of 2.5 and hight of 1.524mm. The design has given good response of bandwidth 15%.
In 1996, Tugonski et al.[36] published a paper that presented a technique which extends the operating bandwidth (defined as having a return loss of less than -10 dB) of the aperture coupled microstrip antenna to over 50%. On the antenna side of the ground plane, a thick slab of Rogers 5880 Duroid is used for the lower substrate, while foam is used for the top substrate. The top patch was etched on a 5 mil thick 5880 Duroid cover layer.
In 1997, Chow and Shiu [37] designed two microstrip antennas, one U-slot on the patch and other H-slot on the ground plane, each antenna fed by probe feed. They have observed that a wide frequency band of operation, 40% bandwidth
experimentally has been
obtained.
In 1999, Rowe with partner [38] has designed a broadband CPW fed stacked patch antenna on a high dielectric constant feed substrate with a bandwidth of 40%, and the antenna was fabricated and tested.
In 2002, Yong et al. [39] has proposed a new design, that is L-probe fed thick-substrate patch antenna mounted on a finite ground plane. This antenna is designed and analyzed by full wave method that is Finite Difference Time Domain (FDTD). The measured and computed values for the bandwidth are 30% and 35%, respectively.
In 2004, another paper was published entitled "A Wideband Circularly Polarized Microstrip Patch Antenna For (5–6)Ghz Wireless LAN Applications", this paper is proposed by Yang et. al. [40] in which a 11% impedance bandwidth was obtained.
In 2005, another published paper about broadband microstrip antenna was presented by Saed [41]. A two-layer microstrip antenna fed by a coplanar waveguide through a slot/loop combination was investigated in this paper. The two layers consist of a highcontaining the feed network and a low-
substrate
substrate containing two patches, one on either
19
CHAPTER ONE
INTRODUCTION
side. The two substrates are not separated by a ground plane. This arrangement produced impedance bandwidth of about 23%.
During the recent years, many efforts have gone into bandwidth enhancement techniques for microstrip antennas. In 2006, the British researcher, Gao and partners [42], have presented simple broadband antenna using only one patch, the designed antenna achieves a bandwidth of 26%. This paper presents a simple broadband proximity coupled microstrip patch antenna. A circular patch is used as the main radiator, and an H-shaped slot is cut in the ground plane below the feed line. A stepped-width microstrip line is used to feed the patch through proximity coupling. In 2007, a new design has been fabricated by Hazdra et al. [43]. This design of the wideband patch antenna is operating with the L-probe feeding mechanism. Such kind of design could provide relative bandwidth more than 30%.
In 2008, another design of microstrip antenna was prepared by Kiran et al. [44]. This antenna is compact broadband stacked dual wide slit loaded rectangular microstrip antenna, designed and fabricated and studied experimentally. The design consist of stacking (h=3.2 mm) of two wide slit load rectangular microstrip patches of the same size. This antenna gave a broad bandwidth 27%.
In 2009, Indian researchers published a new paper about the improvement of BW [45]. In this paper, they propose a circularly polarized (CP) microstrip antenna on a suspended substrate with a coplanar capacitive feed and a slot within the rectangular patch. The antenna has an axial ratio bandwidth (< 3 dB) of 7.1%. The proposed antenna exhibits a much higher impedance bandwidth of about 49%. Another technique to increase BW was published by N. Prombutr with partners [46]. This article presents a bandwidth enhancing technique using a modified ground plane with diagonal edges, rectangular slot, and Tshape cut for the design of compact antennas, they designed a circular patch antenna with 120% impedance bandwidth.
In 2010, Lin proposed a new technique to increase BW [11], a very-wideband microstrip antenna is proposed and studied. The antenna has a simple structure comprising a rectangular patch embedded into a notch cut in the finite ground plane edge. The novel
20
CHAPTER ONE
INTRODUCTION
structure is bent to reduce antenna height and is divided into two resonators: an open loop and a planar monopole. The former simultaneously excites half- and one-wavelength modes to form a wide bandwidth for lower band operation of the design. In addition, the planar monopole with its inherent broadband property provides the upper-band operation. With a small volume of
, the impedance bandwidth of the proposed
antenna is up to 128% impedance bandwidth from 1.80 to 8.23 GHz verified that the design is suitable for wireless laptop.
In 2011, Wang with partner proposed a new design of microstrip antenna, made of a microstrip monopole slot Antenna with unidirectional radiation characteristics. By modifing the width of the ground plane, connecting one metallic finger at the upper right corner, and etching two asymmetrical slits in the ground plane as reflectors, the radiation directivity of the monopole slot antenna can be enhanced. The proposed antenna achieves a measured 97.4% bandwidth at the center frequency of 2.31 GHz.
In this study,
commercial software, the high frequency structure simulator (HFSS) based on the finite element method (FEM) is used [47].
A new design technique for bandwidth enhancement of concentric microstrip annular ring slot antennas was proposed by Rahmani in 2012 [48]. Using this technique, an UltraWide-Band antenna was designed with simulated bandwidth of 111.29%. Using this technique, they obtained an Ultra-wide bandwidth with small size antenna. It may find proper applications in wideband mobile communication system. In 2013, another paper was published entitled "Optimization of Geometry of Microstrip Patch Antenna for Broadband Applications" [49] proposed by Koyya et al. The purpose of the paper is to design wideband rectangular patch antenna printed on FR-4 substrate. Higher bandwidth can be achieved by unsymmetrical feed and a reduction in ground plane with proper gap distance. The rectangular patch antenna worked from 1.4-4GHz at 95% bandwidth with a 2.1 mm wide microstrip line feed.
In 2013, another paper was published by Chattopadhyay et al. [50], in which a wideband microstrip-line-fed hexagonal wide-slot antenna is proposed and experimentally investigated. The hexagonal slot excited by a simple 50 Ω microstrip line with a rotation angle of 0° having 470 MHz bandwidth is considered as a reference antenna. The proposed
21
CHAPTER ONE
INTRODUCTION
hexagonal slot is rotated by 30° and excited by a 50 Ω line loaded by a hexagonal tuning stub. The experimental results exhibit matching impedance below a 2:1 VSWR bandwidth of 5165 MHz (2.117–7.282 GHz) covering all the WiMAX and wireless local area network band applications, the percentage impedance bandwidth was 110% at centre frequency of 4699.5 MHz.
The last antenna presented in this thesis is [51] "A Compact Novel Tapered U Slot Ultra Wideband Antenna". A new small UWB antenna has been designed, simulated, measured and fabricated. The simulation results obtained by Ansoft HFSS software show good agreement with the measured results. The antenna provides excellent performance in the entire operational bandwidth. The antennas are fabricated and the measured impedance bandwidths defined by VSWR<2 are 100% for 10.34GHz (3.66-14GHz) and 10.60GHz (3.4-14GHz) on FR4 substrate.
22
CHAPTER TWO
DESIGN AND ANALYSIS
CHAPTER TWO
DESIGN AND ANALYSIS OF BROADBAND MICROSTRIP ANTENNA
2.1 Introduction to Patch Antenna Various shapes of microstrip antenna patches (square, triangular/rectangular and circular) etched on a dielectric substrate are proposed and investigated. The ground plane dimensions of the proposed antenna are changed or its shape is defected (it is called defected ground structure) by making notches at the surface or/and reducing its length or width. Also the effect of variation in the dielectric constant of the substrate on antenna performance is investigated. The antenna is assumed to be fed by microstrip line. This proposed antenna is analyzed using High Frequency Structure Simulator (HFSS) and the performance (return loss, VSWR, bandwidth, gain, directivity, radiation patterns, and current distribution on the patch) of the designed antenna is studied.
The antenna patch is chosen as assumed perfect conductor. The shapes of antenna patch to be investigated are square, triangular/rectangular and circular. This geometry of the studied patches are shown in (Figs. 2.1) that illustrates the geometry with specifications of these patches.
23
CHAPTER TWO
DESIGN AND ANALYSIS
Wg=Ws a
Wp Wf
Lp
h
Wp Lp
Lf Lg=Ls
(b)
(a)
a
(c) Figure 2.1: Geometry of studied Antenna patches (a) Square (b) Triangular / Rectangular (c) Circular patches.
2.2 Defected Ground Structure (DGS)
The ground plane of the designed antenna is assumed to be a perfect conductor. In this thesis, the defected ground structure is designed as follows.
(a) Reducing the length of the ground plane (Fig. 2.2). (b) Reducing the width of the ground plane (Fig. 2.3). (c) Making a notch at the center of the ground plane edge.(Fig. 2.4) center notch. (d) Making a notch at the right of the ground plane edge.(Fig. 2.5) right notch).
24
CHAPTER TWO
DESIGN AND ANALYSIS
(e) Making a notch at the left of the ground plane edge.(Fig. 2.6) left notch). (f) Making a combination of above notches (Fig. 2.7).
Patch
Ground
Lg=10.5mm m
Wg=30mm
Figure 2.2: Reducing the length of the ground plane (DGS)
Ws =30mm.
Lg=Ls=28mm
Wg=25mm.
Figure 2.3: Reducing the width of the ground plane.
25
CHAPTER TWO
DESIGN AND ANALYSIS
Lnc Wnc
Figure 2.4: Making a notch at the center of the ground plane edge.
Lnr
Wnr
Figure 2.5: Making a notch at the right of the ground plane edge.
26
CHAPTER TWO
DESIGN AND ANALYSIS
Lnl
Wnl
Figure 2.6: Making a notch at the left of the ground plane edge.
Lnr
Lnl Lnc
Wnl
Wnr
Wnc
Figure 2.7: Making a combination of above notches.
2.3Antenna Substrate Material
In this thesis, three types of antenna substrate materials are chosen to be investigated. They are Duroid, FR-epoxy and RogrersTMM10 and have relative permittivities of 2.2, 4.4 and 9.2, respectively. The thickness of these materials is assumed to be h=1.5748 mm. The
27
CHAPTER TWO
DESIGN AND ANALYSIS
effects of these materials on the antenna performance are studied. (Table 2.1) illustrate the characteristics of materials.
Tab. 2.1: Characteristics of proposed materials. Materials
tanδ
h (mm)
Duroid
2.2
0.0009
1.5748
FR-epoxy
4.4
0.02
1.5748
RogrersTMM10
9.2
0.0022
1.5748
2.4 Antenna Analysis and Performance
The designed antennas with different configurations mentioned above are analyzed using HFSS simulator. Each patch shape is supposed to be etched or printed on the studied substrate materials for different proposed defected ground structure DGS (a to f item in section 2.3) and the performance of these antennas design are presented and discussed in chapter 3 in details. The antenna performance can be characterized by the following parameters.
2.4.1 Return Loss
It is the difference between forwarded and reflected power, in dB, generally measured at the input to the coaxial cable connected to the antenna. When an electromagnetic wave travels down a transmission line and encounters a mismatched load or a discontinuity in the line, part of the incident power is reflected back down the line. If the power transmitted by the source is Pt and the power reflected back is Pr, then the return loss is given by P r divided by Pt. For maximum power transfer the return loss should be as small as possible. This means that the ratio Pr/Pt should be as small as possible, or expressed in dB, the return loss should be as large a negative number as possible. Return loss is expressed mathematically by the following equation [52]:
28
CHAPTER TWO
DESIGN AND ANALYSIS
(2.1)
Here
where incident voltage,
(2.2)
=is the reflection coefficient,
= is the reflected voltage,
= is the
are respectively the antenna impedance and characteristic
impedance of the transmission line.
2.4.2 Voltage Standing Wave Ratio (VSWR)
Voltage standing wave ratio is usually noted as VSWR. It gives information about how much of a wave is reflected. VSWR is the ratio between the maximum voltage value of the standing wave and the minimum voltage value along the transmission line. The VSWR is given by: (eq.2.3) [53]:
(2.3)
Where
represents the reflection coefficient ,
and
maximum and
minimum voltage, respectively Such that (2.4)
The VSWR indicates how closely or efficiently an antenna's terminal input impedance is matched to the characteristic impedance of the transmission line. The larger the number of VSWR provides, the greater the mismatch between the antenna and the transmission line.
29
CHAPTER TWO
DESIGN AND ANALYSIS
As it can be seen from the definition, the VSWR will be equal to infinity for total reflection and to 1 for zero reflection. With one meaning that the two transmission lines are perfectly matched. With regards to antenna design, a VSWR that is as low as possible is desired because any reflections between the load and the antenna will reduce the effectiveness of the antenna. A partial standing wave is partially travelling and thereby making a net transport of power. A VSWR of 2:1 will be used as a design guide line and is approximately equal to a return loss of -9.5 dB [54].
2.4.3 Bandwidth
Another important parameter of any antenna is the bandwidth it covers. Only impedance bandwidth is specified most of the time. However, it is important to realize that several definitions of bandwidth exist: impedance bandwidth, directivity bandwidth, polarization bandwidth, and efficiency bandwidth. Directivity and efficiency are often combined as gain bandwidth [55]. The bandwidth of an antenna is defined as “the range of frequencies within which the performance of the antenna, with respect to some characteristics, conforms to a specified standard.” The bandwidth can be considered to be the range of frequencies, on either side of a center frequency (usually the resonance frequency for a dipole), where the antenna characteristics (such as input impedance, pattern, beamwidth, polarization, side lobe level, gain, beam direction, radiation efficiency) are within an acceptable value of those at the center frequency. The percentage bandwidth of a microstrip antenna can be written with respect to resonance frequency as [56]: (2.5) And with respect to center frequency: (2.6) Where
is the upper frequency where the impedance match is S = 1 voltage
standing wave ratio (VSWR) and
is the lower frequency where the impedance match is 30
CHAPTER TWO
DESIGN AND ANALYSIS
also S : 1 VSWR. The VSWR is less than S : 1 over (
−
).
are the resonant
frequency and center frequency of the patch respectively. Generally, S = 2 for most practical applications. The BW is usually specified as frequency range over which VSWR is less than 2 (which corresponds to the return loss of -9.5dB or 11% reflected power) [57].
For broadband antennas, the bandwidth is usually expressed as the ratio of the upperto-lower frequencies of acceptable operation. For example, a 10:1 bandwidth indicates the upper frequency is 10 times greater than the lower. For narrowband antennas, the bandwidth is expressed as a percentage of the frequency difference (upper minus lower) over the resonant frequency. For example, a 5 percent bandwidth indicates that the frequency difference of acceptable operation is 5 percent of the resonant frequency. The plot (Fig. 2.8) shows the return loss of a patch antenna and indicates the return loss bandwidth at the desired S11/VSWR (S11wanted/VSWR wanted). The bandwidth is typically limited to a few percent [55,58].
S11=-10 dB
fr-Δfr
fr
fr+Δfr
Figure 2.8: Bandwidth of MSPA [55].
31
CHAPTER TWO
DESIGN AND ANALYSIS
2.4.4 Directivity and Gain
Directivity D is defined as the ratio of the radiation intensity U in a given direction from the antenna to the radiation averaged over all direction. The average radiation intensity is equal to the total power radiated by the antenna
divided by
. So the directivity can
be calculated by [59]:
(2.7)
If not specified, antenna directivity implies its maximum value, i.e.,
.
(2.8)
(2.9)
To normalization factor
is the total radiated power divided by
(power per unit
solid angle):
(2.10)
To better understand the role of the normalization factor, let us consider an isotropic antenna, which radiates an equal amount of power in all directions. Then
(2.11)
1 < D < infinity, for isotropic antenna D=1, usually this ratio is expressed in
decibels, and these units are referred to as "decibels-isotropic" (dBi). And D=0dB in any direction. Any other directional antenna must therefore have directivity above 0dB (in the direction of maximum radiation) and below 0dB (in the direction of minimum radiation). The gain of the antenna is related to the 32
CHAPTER TWO
DESIGN AND ANALYSIS
directivity of the antenna. Gain takes into account the directional capabilities as well as the efficiency of the antenna [60]. The gain of an antenna (in a given direction) is defined as “the ratio of the radiation intensity in a given direction to the radiation intensity that would be obtained if the power fed to the antenna input were radiated isotropically”. The radiation intensity corresponding to the isotropically radiated power is equal to the power from the generator to the antenna input divided by 4π. Mathematically this can be expressed as
(2.12)
Antenna gain G is closely relates to the directivity, but it takes into account the radiation efficiency
of the antenna as well as its directional properties, as given by:
(3.13)
3.4.5 Radiation Pattern
Radiation pattern is defined as a mathematical function or a graphical representation of the radiation properties of the antenna as a function of the spatial coordinates. It is determined in the far-field region and is represented as a function of the directional coordinates. It is measured by moving the test antenna around the probe antenna at a constant distance from it, or vice versa. The radiation patterns are normally taken in to two orthogonal planes, often named the E and H-planes [61-62].
A graph of the spatial variation of the power density along a constant radius is called an amplitude power pattern. Antenna radiation patterns usually take two forms, the elevation pattern and the azimuth pattern. The elevation pattern is a graph of the energy radiated from the antenna looking at it from the side (E-Plane). The azimuth pattern is a graph of the energy radiated from the antenna as if you were looking at it from directly above the
33
CHAPTER TWO
DESIGN AND ANALYSIS
antenna (H-Plane). The basic radiation pattern of a dipole antenna is shown in (Fig. 2.9) [63]. An antenna's radiation pattern is the characteristic that most affect system coverage and performance. All antennas do not radiate more total energy than is delivered to their input connector. Antenna radiation patterns are typically presented in the form of a polar plot for a 360° angular pattern in one of two sweep planes and it is presented on a relative power dB scale.
Figure 2.9: Radiation pattern of dipole antenna [63].
Main lobe is the radiation lobe containing the direction of the maximum radiation. For side lobe, it is a radiation lobe in any direction other than the intended lob direction. It is usually adjacent to the main lobe and occupies the hemisphere in the direction of the main beam. A radiation lobe is another type of dipole antenna in which axis is at 180° with respect to the main beam. It usually refers to a small lobe that occupies the hemisphere in a direction opposite to a main lobe that is known as back lobe [53].
34
CHAPTER TWO
DESIGN AND ANALYSIS
2.5 High Frequency Structure Simulator (HFSS)
The antenna analyzes is performed using the High Frequency Structure Simulator (HFSS), commercial computer software package from Ansoft Technologies, which is based on the finite element method (FEM) technique for arbitrary 3D volumetric passive devices. It helps the user to observe and analyze various electromagnetic properties of the structure such as radiation patterns and scattering parameters. The windows of HFSS software are as shown in (Fig. 2.10) [64].
Figure 2.10: HFSS windows displays.
Finite element method, or commonly called finite element analyze is a method of solving differential equation inside geometry to obtain solution of electromagnetic fields where it is governed by boundary conditions and system of differential equations. HFSS is 3D EM simulation software which is produced for RF and wireless design by Ansoft Company. At the first time, it was introduced as first commercial software simulating complex 3D geometrics in 1990. The software allows the design engineers to use the finite element method. Analyzing antennas, waveguide components, RF filters and many other structures are as simple as drawing the structure, specifying material characteristics, and identifying ports and special surface characteristics. HFSS automatically generates field solutions, port characteristics, and s-parameters. It is quickly able to calculate antenna metrics such as gain, directivity, far-field pattern cuts, far-field 3D plots, and 3dB
35
CHAPTER TWO
DESIGN AND ANALYSIS
beamwidth [24]. (Figures 2.11-2.13) illustrates the input data, validation with running the software and the output of the HFSS software.
Figure 2.11: Create the dimensions of the MSPA by HFSS.
Figure 2.12: Check the validation of the MSPA for errors.
Figure 2.13: The output windows of HFSS software.
36
CHAPTER TWO
DESIGN AND ANALYSIS
HFSS divides the geometric model into a large number of tetrahedral elements. Each tetrahedron is composed of four equilateral triangles and the collection of tetrahedral forms what is known as the finite element mesh [65], as shown in (Fig. 2.14).
Patch mesh
Substrate mesh
Figure 2.14: Finite element mesh of MSPA.
At each vertex of the tetrahedron, components of the field tangential to the three edges meeting at that vertex are stored. The other stored component is the vector field at the midpoint of selected edges, which is also tangential to a face and normal to the edge. Using these stored values, the vector field quantity such as the H-field or the E-field inside each tetrahedron is estimated. A first-order tangential element basis function is used for performing the interpolation. Maxwell’s equations are then formulated from the field quantities and are later transformed into matrix equations that can be solved using traditional numerical techniques. By using HFSS, one can compute the following parameters [66-67]:
Basic electromagnetic field quantities and, for open boundary problems, radiated near and far fields.
Characteristic port impedances and propagation constants.
Generalized S-parameters and S-parameters renormalized to specific port impedances.
37
CHAPTER TWO
DESIGN AND ANALYSIS
The eigenmodes, or resonances, of a structure.
2.6 Antenna Test by HFSS Software To make sure that the results, carried out by the HFSS software, are right the following steps have been performed:
1- We brought an actual microstrip patch antenna with resonance frequency of (9.5 GHz).
2- All dimensions of actual microstrip patch antenna were measured.
3- Then we have designed by HFSS software the actual antenna, in order to make a comparison between the actual antenna and the software designed.
We have concluded that the frequency of designed microstrip patch antenna by HFSS software was close to the actual antenna, which was (9.42GHz) and it was the close to actual one (9.5GHz). The following (Figs. 2.15) represents the actual microstrip and simulated (or designed) antennas.
(a)
(b)
Figure 2.15: (a) The actual MSP antenna, (b) The designed MSP antenna by HFSS software.
38
CHAPTER TWO
DESIGN AND ANALYSIS
( Figures 2.16 and 2.17) represent the impedance bandwidth and gain of actual antenna were designed by HFSS software. Return Loss of proposed antenna 9.42GHz.
Patch_Antenna_ADKv1
ANSOFT
0.00 -5.00 Name X Y Curve Info m1 9.4259 -30.2404
-10.00
S11 dB
-15.00 -20.00 -25.00 m1
-30.00 -35.00
4.00
6.00
8.00
10.00 Freq [GHz]
Figure 2.16: Return loss of actual antenna by HFSS.
Figure 2.17: Gain of actual antenna by HFSS.
39
12.00
14.00
16.00
CHAPTER TWO
DESIGN AND ANALYSIS
Baskaran with partners have been observed the partial ground plane of microstrip patch antenna by CST software and practically, and they got agreement very well result between simulated and practical results. (Fig. 3.18) represent the manufactured partial ground plane MSPA. This is to support my work (MSPA with DGS) [68].
Patch
Lg
Figure 2.18: Fabricated MSPA with partially ground plane [68].
40
CHAPTER THREE
RESULTS AND DISCUSSION
CHAPTER THREE
RESULTS AND DISCUSSION
3.1 Introduction
After studying the concept of a microstrip antenna and its characteristics in the first chapter, and in this chapter will discuss the procedures used to design the configurations of the
proposed microstrip patch antennas. Also, in this chapter, a broad overview will be given in terms of the various techniques that are currently available to enhance the bandwidth of patch antennas and the radiation characteristics for each of the designs will be discussed . Since the
basic
configurations
for
standard
microstrip antennas are
square,
rectangular/triangular and circular patches printed on an inexpensive Duroid substrate a low dielectric constant (
) and high (h=1.5748mm), the work presented here is
based on those simple geometries. The idea was to develop new configurations by modifying Defect Ground Structure (DGS) with notches. The performance of the antennas was analyses by HFSS software.
3.2 Design and Performance of Square Microstrip Patch Antenna
The radiating element is selected to be a square patch
and printed on
an inexpensive Duroid substrate. This material is light weight, and possesses a low dielectric constant (
). It also has uniform electrical properties over a wide
frequency range. In order to achieve a high radiation power without increasing the antenna weight and the dielectric loss, a 1.5748 mm thick substrate is selected from the available
41
CHAPTER THREE
RESULTS AND DISCUSSION
commercial Duroid substrate as shown in (Fig. 3.1). A 50Ω microstrip line is used to feed the MSP antenna, and is printed on the same substrate. On the other side of the substrate, there is a ground plane below the microstrip feed line. This ground plane is chosen to be (
on the other sides of substrate. The patch dimensions are
selected to be
on the top of the substrate and the width and length
of the feed line are
. The geometry and dimensions of this antenna
design are illustrated in (Fig. 3.1) and (Tab. 3.1)
Wp S=2mm h
Lp
Wf Lf
Lg=Ls Wg=Ws
Figure 3.1: Structure of square microstrip patch antenna (MSPA).
Table 3.1: Dimensions of proposed square patch antenna.
Name and dimensions Substrate material
Duroid
Thickness of substrate (h)
1.5748 mm.
Length of ground plane
28 mm
Width of ground plane
30mm.
Length and width of patch
14 mm. 14 mm.
Feed width and length Loss tangent (tanδ)
0.0009
42
CHAPTER THREE
RESULTS AND DISCUSSION
Using HFSS simulator¸ the above antenna design is analysed. The result of return loss characteristics are shown in (Fig. 3.2). Return loss is a parameter which explains amount of power from feed point to radiating element is supplied effectively.
Square microstrip patch antenna without modifications.
Patch_Antenna_ADKv1
ANSOFT
5.00 -0.00 -5.00
S11 dB
Name X Y Curve Info Normal_Ground 14.2613 -20.2053
-10.00 -15.00 Normal_Ground
-20.00 -25.00
0.00
5.00
10.00
15.00 Freq [GHz]
20.00
25.00
30.00
Figure 3.2: Variation of S11 versus frequency of normal SMSPA.
The bandwidth percentage of the square patch antenna can be found by referring to resonant frequency or center frequency. The bandwidth percentage of the patch antenna can be calculated when its return loss becomes -10dB [69]. The resulting antenna bandwidth is summarized in (Tab. 3.2). Table 3.2: Parameters of proposed SMSPA.
Parameters
Value 15.12 GHz. 13.62 GHz. 14.26 GHz. 1.5 GHz. 10.5 %
43
CHAPTER THREE
RESULTS AND DISCUSSION
The bandwidth percentage of square microstrip patch antenna without modifications is 10.5%. The 3D view for the gain and directivity of
the antenna without DGS is also
shown in (Fig. 3.3), the maximum gain is 6.9dB. The 2D radiation pattern of antenna is also shown in (Fig. 3.4) in which the fields are presented. In this radiation pattern both E and H planes are also presented.
(a)
(b)
Figure 3.3: 3D Polar plot of SMSP antenna: (a)Gain (b)Directivity without DGS at 14.26 GHz.
E-plane
Patch_Antenna_ADKv1
ANSOFT
Curve Info
0
3.00
dB(GainTotal) Setup1 : LastAdaptive Freq='14GHz' Phi='90deg'
-4.00
dB(GainTotal)_1 Imported Freq='14GHz' Phi='0deg'
-30
30
-60
60 -11.00 -18.00
-90
90
-120
120
-150
----- E-Plane ----- H-Plane
150 -180
Figure 3.4: 2D Radiation pattern of SMSP antenna at 14.26GHz
3.2.1 Design and Performance of SMSP Antenna with DGS
(Fig. 3.5) represents the geometry of square patch with DGS. By reducing the length of ground plane from 28mm to 20mm, 12mm, 10.5mm and 8mm as shown in (Figs. 3.6, 44
CHAPTER THREE
RESULTS AND DISCUSSION
3.7, 3.8 and 3.9) respectively and summarized in (Tables 3.3, 3.4, 3.5 and 3.6) respectively. It is noticeable that the antenna design with Lg=20mm gives three resonant frequencies (13.53GHZ, 17.32GHZ and 23.87GHz) for three bands and illustrate in (Tab. 3.3). It is observed that the antenna bandwidth increases for all bands.
Ls
Wg=Ws Wp
Lp
Lf
Wf
Figure 3.5: Defect ground structure (DGS) of SMSP antenna. .
Patch_Antenna_ADKv1 Curve Info
ANSOFT
0.00
-12.50
S11 dB
Name
X
Y
m1
13.5327 -27.5932
m2
17.3216 -26.1651
m3
23.8794 -36.3107
m2
-25.00
m1
m3
-37.50
0.00
5.00
10.00
15.00 Freq [GHz]
20.00
25.00
30.00
Figure 3.6: Variation of SMSP antenna Return loss versus frequency operation with DGS of (Lg=20mm.)
Table 3.3: SMSP antenna parameters with DGS of Lg=20mm. Length of the ground Lg=20mm.
S11 dB.
BWr%
BWc%
First band
12.5
15.5
13.53
-27
22%
21%
Second band
15.6
18.3
17.32
-26
15.6%
15%
20.22
28.85
23.87
-36
34%
33%
Third band
45
CHAPTER THREE
RESULTS AND DISCUSSION
When the ground plane is reduced to12mm, two resonant frequencies (4.64 GHz and 12.07GHz) for two bands of operation are obtained as shown in (Fig. 3.7) and (Tab. 3.4). Also the bandwidth of the antenna increases for each band. .
Curve Info Patch_Antenna_ADKv1
ANSOFT
0.00 -2.50
Name
-5.00
X
Y
m1
4.6432 -17.6655
m2
12.0754 -19.9810
S11 dB
-7.50 -10.00 -12.50 -15.00 m1
-17.50
m2
-20.00
0.00
5.00
10.00
15.00 Freq [GHz]
20.00
25.00
30.00
Figure 3.7: Variation of SMSP antenna Return loss versus frequency operation with DGS of (Lg=12mm.)
Table 3.4: SMSP antenna parameters with DGS of Lg=12mm. Length of the ground Lg=12mm.
S11 dB.
BWr%
BWc%
First band
3.87
6.07
4.64
-17.66
47%
44%
Second band
10
14.5
12.07
-19.98
37%
36%
The reduction in the length of ground plane to 10.5mm results in a return loss values described in (Fig. 3.8) and in (Tab. 3.5). In this case the designed antenna resonates at 4.2 GHz with return loss of -26.5dB. It is noticed that the bandwidth with respect to resonance frequency was increases to 185% compared with 12% bandwidth of the antenna design without DGS.
46
CHAPTER THREE
RESULTS AND DISCUSSION
Lg=10.5mm.
Patch_Antenna_ADKv1
ANSOFT
0.00 Name X Y Curve Info Lg_105m m 4.2060 -26.5561
-5.00
S11 dB
-10.00 -15.00 -20.00 -25.00 -30.00
Lg_105m m
0.00
5.00
10.00
15.00 Freq [GHz]
20.00
25.00
30.00
Figure 3.8: Variation of SMSP antenna Return loss versus frequency operation with DGS of (Lg=10.5mm.)
Table 3.5: SMSP antenna parameters with DGS of Lg=10.5mm. Length of the ground Lg=10.5mm. Lg=10.5mm.
3.52
11.3
4.2, 11
S11 dB.
BWr%
BWc%
-26.5
185%
104%
The final case of length reduction is Lg=8mm and the behavior of return loss is shown in (Fig. 3.9) and summarizes in (Tab. 3.6). Also the resonant frequency is shifted to 3.71GHz and the antenna bandwidth decreased with respect to the other previews DGSs.
47
CHAPTER THREE
RESULTS AND DISCUSSION
Lg=8mm.
Patch_Antenna_ADKv1
ANSOFT
0.00 Name X Y Curve Info Lg_8mm 3.7136 -15.1505
-5.00
S11 dB
-10.00 Lg_8mm
-15.00
-20.00
-25.00
0.00
5.00
10.00
15.00 Freq [GHz]
20.00
25.00
30.00
Figure 3.9: Variation of SMSP antenna Return loss versus frequency operation with DGS of (Lg=8mm.)
Table 3.6: SMSP antenna parameters with DGS of Lg=8mm. Length
of
the
ground Lg=12mm. Lg=8mm.
3.21
4.23
3.71
S11 dB.
BWr%
BWc%
-15.15
27%
27%
The comparison between the performance of the studied antenna designs are shown in (Fig. 3.10) and (Tab. 3.7).
--- Lg=28mm. --- Lg=20mm. --- Lg=12mm. --- Lg=10.5mm. --- Lg=8mm.
Figure 3.10: Variation of SMSP antenna Return loss versus frequency operation without DGS and with various DGS cases.
48
CHAPTER THREE
RESULTS AND DISCUSSION
Table 3.7: Comparisons between the SMSP antenna parameters for different DGS cases and without DGS. Length of the ground (Lg mm.)
S11 dB.
BWr%
BWc%
13.62
15.12
14.26
-20
10.5%
10.4%
12.5
18.26
13.53
-27
42%
37%
15.6
18.3
17.32
-26
15.6%
15%
20.22
28.35
23.87
-36
34%
33%
3.87
6.07
4.64
-17.66
47%
44%
10
14.5
12.07
-19.98
37%
36%
Lg =10.5mm.
3.52
11.3
4.2
-26.5
185%
104%
Lg =8mm.
3.21
4.23
3.71
-15.15
27%
27%
Lg=28mm.
Lg =20mm.
Lg =12mm.
It is clear that the antenna design with DGS (Lg=10.5mm) displays the best performance compared with the others. Since the resonant frequency of this design is 4.2GHz which is less than 14.26GHz of the antenna design without DGS, therefore, the miniaturization in antenna size is achieved.
3.2.2 SMSP Antenna with DGS and Notches With fixing the ground plane at a length of 10.5mm, different notch shapes at different locations are made at the edge of the selected ground plane and investigated. The use of DGS notch leads to disturb the shield current distribution in the ground plane which influences the input impedance and current flow to the antenna [70]. Different notches including, center, right, left and combination of them with variation dimensions are studied as describe below.
49
CHAPTER THREE
RESULTS AND DISCUSSION
1-At first, we choose only one notch at the edge center of ground plane with different dimensions to get the best performance.
A center notch of dimension
is
supposed as plotted in (Fig. 3.11) and different dimensions are tested. (Figs. 3.12) and (Tab. 3.8) show the return loss characteristics of the square patch antenna for different dimensions of center notch.
Ln W
c
nc
(b)
(a)
Figure 3.11: Square patch (a) Defect ground plane (DGS) with center notch, Patch with DGS and center notch.
---------
(b)
Wn× Ln 2.7 × 8 5×6 2×6 2.7 × 5
Figure 3.12: Characteristics of SMSP antenna return loss at center notch with Difference Dimensions.
50
CHAPTER THREE
RESULTS AND DISCUSSION
Table 3.8: SMSP Antenna parameters with GDS and center notch. DGS with notch
Notch1
Notch2 . Notch3 . Notch4
BWr%
BWc%
3.56
11.25
4.49
-20.64
171%
103%
3.65
7.8
6.24
-41.99
66%
72%
3.56
13
4.2060
-22.21
224%
107%
3.56
13.76
4.2060
-2083
242%
117%
.
Now, it is clear that the antenna with
center notch or with
center notch gives a good performance of 224% or 242% bandwidth respectively compared with 185% bandwidth of the antenna without center notch.
2-Different combinations of center, right and left notches are also supposed and three types of antenna are assumed to be investigated. Antenna No.1 represents a square patch with DGS of center notch center notch
only, and the antenna No.2 is a square patch with DGS of and right notch
, while the third antenna No.3 consists of
a square patch with DGS of center notch
, right notch
and left notch
. The dimensions of studied notches for three antennas are illustrated in (Tab. 3.9). The return loss properties of the three antennas are shown in (Fig. 3.13) and (Tab. 3.10). It is noted that the increasing of notches (two notches or three notches) leads to increase percentage bandwidth (264% and 345% respectively) compared with 242% bandwidth of antenna No.1 with DGS of one notch. To improve the bandwidth of the proposed antennas, the defect ground structure is modified by cutting three notches, and we chose the optimum result of three notches. These result like Bhavanam result (practical and simulated) [71], he had observed partial ground plane is modified by cutting semi-elliptical shaped notches on its top edge. In antenna 3 due to insertion of three notches in DGS, bandwidth further increased.
51
CHAPTER THREE
RESULTS AND DISCUSSION
Table 3.9: Dimensions of notches in defect ground structure of SMSP antennas. Antennas Antenna1
2.7 × 5
Antenna2
3×4
3 × 0.5
Antenna3
4×4
5×1
4×2
--- DGS+1Notch. --- DGS+2Notches. --- DGS+3Notches.
Figure 3.13: Characteristics of
versus Frequency for SMSP antenna with DGS
and with different notches cases.
Table 3.10: Parameters of SMSP antenna with DGS and with different notch cases.
S11 dB. BWr%
DGS with notch
Antenna1
3.5
13.7
BWc%
4.206
-20.83
242%
118%
4.351
-19.11
264%
124%
4.06
-19.35
345%
134%
0 Antenna2
3.5
15 8
Antenna3
3.42
17.45
In order to understand the radiation behavior, the current distribution of square patch design is simulated at the resonate frequency (4.06GHz) and the results are illustrated in Fig. (3.14). It was a reasonably strong distribution of currents at the bottom and side edges 52
CHAPTER THREE
RESULTS AND DISCUSSION
of the ground plane or the current distributions were denser at the bottom and side edge (center notch) of the ground plane. This observation, incidentally, provides support to the fact that the ground plane affects the antenna performance.
Figure 3.14: Current distrbution on the DGS at one, two and three notches.
The radiation characteristics of antenna No.3 (SMSP antenna with DGS and 3notches) are presented. The maximum gain at frequency of 4.06 GHz is 2.8966dB, this approaches omnidirectional radiation pattern, shown in (Figs. 3.15a). An omnidirectional antenna is a class of antenna which radiates radio wave power uniformly in all directions in one plane, with the radiated power decreasing with elevation angle above or below the plane, dropping to zero on the antenna's axis. While the directivity is 2.8982 dB as shown in (Figs. 3.15b).
53
CHAPTER THREE
RESULTS AND DISCUSSION
(a)
(b)
Figure 3.15: 3D Polar plot (a) Gain and, (b) Directivity of SMSP antenna with DGS and 3 notches.
(Fig. 3.16) shows the (2D) radiation patterns of the SMSP antenna with DGS and 3notches, in both principal planes of E-plane and H-plane, are obtained at the corresponding simulated resonant frequencies (4.06GHz). Radiation Pattern of DGS with three notches SMSP antenna at resonance frequency. 0 -30
Curve Info dB(GainTotal) Setup1 : LastAdaptive Freq='4.06GHz' Phi='90deg'
30 1.00
dB(GainTotal)_1 Imported Freq='4.06GHz' Phi='0deg'
-3.00 -60
60 -7.00 -11.00
-90
90
-120
120
----- E-Plane ----- H-Plane
-150
150 -180
Figure 3.16: E & H Plane pattern at resonance frequency 4.06GHz.
54
ANSOFT
CHAPTER THREE
RESULTS AND DISCUSSION
(Fig. 3.17) shows the VSWR values for antenna No. 3. The results show a satisfactory outcome that is less than 2. And surface current distributions on the patch shown in (Fig. 3.18).
VSWR of DGS with three notches SMSP antenna.
Patch_Antenna_ADKv1
ANSOFT
5.00 Name X Y Curve Info VSWR 4.0603 1.2414
4.50 4.00
VSWR
3.50 3.00 2.50 2.00 1.50 1.00
VSWR 0.00
5.00
10.00
15.00 Freq [GHz]
20.00
25.00
Figure 3.17: VSWR versus frequency of the proposed antenna structure.
( Figure 3.18: Surface current distributions on SMSP antenna with DGS and 3notches.
55
30.00
CHAPTER THREE
RESULTS AND DISCUSSION
3.3 Triangular/Rectangular Microstrip Patch Antenna
The geometry of a triangular patch combined with rectangular patch is shown in (Fig. 3.19). The antenna dimensions are illustrated in (Tab. 3.11). The triangular patch at the center of the substrate, and step by step accommodated with rectangular patch and shift the triangular patch to the upper side of substrate. The current distribution of triangular/rectangular patch is shown in (Fig. 319b). For these parameters are clear that the triangular patch combined with rectangular patch at difference patch lengths has the best performance of resonance frequency and return loss when the patch length L p=9mm as shown in (Figs. 3.20).
a Wp
Lp
Wf
(b)
(a) Figure 3.19: Triangular/Rectangular patch shape, (a) Current distribution, (b) Normal patch.
56
Lf
CHAPTER THREE
RESULTS AND DISCUSSION
Table 3.11: Dimensions of proposed triangular/rectangular microstrip patch (T/RMSP) Antenna. Parameters
Dimensions
a is sides of triangular
10 mm.
High of substrate (h)
1.5748 mm.
Width and Length of ground
(30×28) mm2
width and Length of the patch
(14×9) mm2.
Feed width and length Relative permittivity of dielectric(Duroid)
2.2
Figure 3.20: Characteristics of Return Loss versus frequency for TMSP antenna accommodated with rectangular Patch.
Table 3.12: Comparisons between the T/RMSP antenna parameters for different patch lengths. Patch length Lp mm.
S11 dB.
BWr%
BWc%
Lp= 0
18.8
30
29.7
-21.7
-
-
Lp= 5
24.3
30
30.21
-18.75
-
-
Lp= 9
24.7
30
25.94
-39.5
-
-
Wp=14mm. a=10mm.
57
CHAPTER THREE
RESULTS AND DISCUSSION
The return loss characteristics of this antenna design at Lp=9mm without DGS are plotted in (Fig. 3.21), and the (Tab. 3.13) illustrate the best performance of T/RMSP antenna at (Lp=9mm). Triangular microstrip patch antenna with normal patch and ground.
Patch_Antenna_ADKv1
ANSOFT
0.00 Name m1
-5.00
X Y Curve Info 25.9447 -39.5013
-10.00
S11 dB
-15.00 -20.00 -25.00 -30.00 -35.00 m1
-40.00
0.00
5.00
10.00
15.00 Freq [GHz]
20.00
25.00
30.00
Figure 3.21: Characteristics of Return Loss versus frequency of T/RMSP antenna at Lp=9mm Without DGS.
Table 3.13: Characteristics of T/RMSP antenna at Lp=9mm Without DGS. Length of the ground(mm.) Lg =28mm.
23.5
30
25.94
S11 dB.
BWr%
BWc%
-39.5
-
-
3.3.1 Design and Performance of T/RMSP Antenna with DGS The dimensions of the ground plane of the proposed antenna is
28
.2. Reducing the length of the ground plane from 28mm to 8mm leads to enhance
the bandwidth like what happens in square patch as shown in (Fig. 3.22).
It is observed that the bandwidth enhancement is performed by reducing the ground length especially at Lg= 10.5mm in which BWr%= 214% and a return loss =-26.67dB, in addition to size miniaturization for the antenna patch is achieved by this method since the resonant frequency 25.94GHz decreases to a lower value up to 3.76GHz as the ground length is reduced. The simulated results are tabulated in (Tab. 3.14) along with the corresponding reduction length of the ground plane for the investigated antennas. 58
CHAPTER THREE
RESULTS AND DISCUSSION
----- Lg=28mm. ----- Lg=20mm. ----- Lg=12mm. ----- Lg=10.5mm ----- Lg=8mm.
Figure 3.22: Return losses versus frequencies curves at difference ground plane length.
Table 3.14: Parameters of T/RMSP antenna at different ground plane length. Length of the ground(mm.)
S11 dB.
BWr%
BWc%
23.5
<30
25.94
-39.5
-
-
16.7
18.7
17.75
-32.16
11%
11%
10.51
13.85
12.94
-30.15
25%
27%
19.8
<30
21.98
-32.37
-
-
Lg =12mm.
9.63
14.7
11.78
-42.23
43%
41%
Lg =10.5mm.
3.76
13.3
4.49
-26.67
214%
111%
Lg =8mm.
3.24
5
3.76
15.24
47%
42%
Lg =28mm. Lg =20mm.
3.3.2 T/RMSP antenna design and performance with DGS and Notches
Three antenna designs with DGS and notches are supposed. Antenna No.1 is DGS of with one center notch and antenna NO.2 is DGS with two notches (center and right notches while antenna No.3 represents patch with DGS of three notches (center, right and left notches) the dimensions of the proposed notches are shown in the (Tab. 3.15). The results of the antenna analysis for return loss properties are introduced in (Fig. 3.23). After
59
CHAPTER THREE
RESULTS AND DISCUSSION
changed more than ten times of the position and area of the notches, we choose the optimum result of position and dimensions notches. It is noted that a bandwidth of 12.3 GHz (2.33-14.63) GHz for (DGS with one notch) is achieved and the percentage impedance bandwidth is 276% at minimum return loss -29.61dB is obtained while the percentage bandwidth of 323% with return loss of -23dB is obtained for antenna NO.3 with three notches.
Table 3.15: DGS with Notch Dimensions of T/RMSP Antennas. DGS+Notches Antenna No.1 DGS+1Notch
Antenna No.2 DGS+2Notches
Antenna No.3 DGS+3Notches
-----DGS+1Notch -----DGS+2Notches -----DGS+3Notches
Figure 3.23: Characteristics of
versus Frequency for T/RMSP antenna with DGS and
with different notches cases.
60
CHAPTER THREE
RESULTS AND DISCUSSION
Table 3.16: Parameters of T/RMSP antenna with DGS and with different notch cases. DGS with notch S11 dB.
BWr%
BWc%
Antenna No.1 DGS+One
2.33
14.63
4.49
-29.61
276%
145%
3
13.8
4.206
-31
256%
128%
3.52
17.14
4.206
-23
323%
132%
Notch Antenna No.2 DGS+Two Notches Antenna No.3 DGS+Three Notches
Fig.(3.24) shows the Voltage Standing wave Ratio (VSWR) of performance T/RMSP antenna DGS with 1notch characteristics and the results show that the antenna has an acceptable performance with VSWR ≤ 2, at resonance frequency (4.49GHz) VSWR=1.06.
VSWR of DGS with one notch of TMSP antenna.
Patch_Antenna_ADKv1
ANSOFT
2.75 2.50
Name CurveXInfo Y 4.4975 1.0684
VSWR
2.25
VSWR
2.00 1.75 1.50 1.25 VSWR
1.00
0.00
5.00
10.00
15.00 Freq [GHz]
20.00
25.00
Figure 3.24: VSWR of T/RMSP antennas with DGS and 1notch at 4.49 GHz.
61
30.00
CHAPTER THREE
RESULTS AND DISCUSSION
In addition, the 2D radiation pattern illustrates that field focusing have been achieved at 4.49 GHz as in (Fig. 3-25) allowing a visualization 2D radiation pattern for phi = 90°(Eplane) and phi = 0° (H-plane) at the resonance frequency of 4.49 GHz.
2D radiation pattern of DGS with one notch TMSP antenna at 4.5GHz.
Patch_Antenna_ADKv1
ANSOFT
0 -30
30 1.50 -2.00
-60
60 -5.50 -9.00
-90
90
-120
120
----- E-plane ----- H-plane -150
150 -180
Figure 3.25: 2D Radiation pattern of T/RMSP antenna with DGS and 1notch at 4.49 GHz.
Moreover, (Figs. 3.26a and 3.26b) represent the gain and directivity of T/RMSP antenna without modifications. The 3D plot of the final design T/RMSP antenna radiation pattern illustrates a field focusing and gain enhancement in the broadside direction as shown in (Fig. 3.26c). The maximum gain of T/RMSP antenna with DGS and 1notch is achieved at resonance frequency 4.49 GHz with 3.0756 dB in the broadside direction. The directivity of the antenna radiation is observed and resulted as 3.0792dB as shown in (Fig. 3.26d).
62
CHAPTER THREE
RESULTS AND DISCUSSION
(
(
a)
b)
(c)
(d)
Figure 3.26: 3D plot, (a) Gain, (b) Directivity of T/RMSP antenna without DGS. (c) Gain and (d) Directivity of T/RMSP antenna with DGS and 1notch at resonance frequency 4.49 GHz.
3.4 Design and Performance of Circular Patch Without DGS A circular microstrip antenna has been designed using the HFSS software based on FEM, which consists of a circular patch of radius (a=9mm) printed on a dielectric substrate of thickness (h=1.5748mm) and relative permittivity (εr=2.2). The antenna is fed by strip line of dimensions
, the antenna ground plane is in rectangular
shape with dimension of
. (Fig. 3.27) shows the geometry of a
proposed circular patch antenna.
63
CHAPTER THREE
RESULTS AND DISCUSSION
a
Lf Lg
Wf
Wg
Figure 3.27: Structure of circular microstrip patch CMSP antenna.
The characteristics of the return loss for this antenna design are illustrated in (Fig. 3.28). The resonant frequency of this patch is 13.38GHz and gives – 33.97dB return loss. Return Loss of Circular Patch without modifications.
Patch_Antenna_ADKv1
ANSOFT
0.00 -5.00 Name X Y Curve Info Cir cular _Patch 13.3869 -33.9724
-10.00
S11 dB
-15.00 -20.00 -25.00 -30.00 Cir cular _Patch
-35.00
0.00
5.00
10.00
15.00 Freq [GHz]
20.00
25.00
30.00
Figure 3.28: Characteristics of return loss versus frequency CMSP antenna without modifications.
3.4.1 Optimization of Patch Radius In the previous results, the radius of the circular patch was 9mm; therefore, the patch radius is changed from 7mm to 9mm for this optimization. The ground plane dimensions are fixed at
. The results of return loss are given in (Fig. 3.29)
and (Tab. 3.17).
64
CHAPTER THREE
RESULTS AND DISCUSSION
----- r= 7mm. ----- r= 7.5mm. ----- r= 8mm. ----- r= 8.5mm ----- r= 9mm.
Figure 3.29: Characteristics of return loss versus frequency for CMSP antennas with various radius and with DGS (Lg=10.5mm).
Table 3.17: Parameters of CMSP antennas with various radius and with DGS (Lg=10.5mm). Radius of patch(mm.)
S11 dB.
BWr%
BWc%
r=7mm.
3.7
6
4.35
-29.57
52%
47%
r=7.5mm.
3.63
5.72
4.35
-26.36
48%
44%
r=8mm.
3.56
5.6
4.20
-25.53
48%
44%
r=8.5mm.
3.50
5.5
4.06
-23.96
49%
44%
r=9mm.
2.47
6
3.91
-34.68
90%
83%
It is noted that circular patch of radius 9mm gives good performance (BWr=90% and S11=-34.68dB).
65
CHAPTER THREE
RESULTS AND DISCUSSION
3.4.2 Design and Performance of circular patch with DGS
In this section, the characteristics of the circular patch with DGS are presented. The ground plane is partially removed in such a way that the length of the ground plane
is
reduced from 28 mm (perfect ground) to 8 mm (partially ground).
The
properties
of
the
patch
return
loss
are
obtained
for
as plotted in (Fig. 3.30). From the graphs, it is also observed that the resonant frequency of the patch decreases (from 13.38GHz to 3.62GHz) as the ground length decreases (from Lg=28mm to Lg=8mm), but
increases from -
33.97dB to -19.8dB. The maximum bandwidth 48% is obtained when Lg=10.5mm for resonant frequency of 4.2GHZ, it is clear in (Tab. 3.18).
----- Lg=28mm. ----- Lg=20mm. ----- Lg=12mm. ----- Lg=10.5mm ----- Lg=8mm.
Figure 3.30: Variation of CMSP antenna return loss versus frequency without DGS and with various DGS cases.
66
CHAPTER THREE
RESULTS AND DISCUSSION
Table 3.18: Comparisons between the CMSP antenna parameters for different DGS cases. Length of the ground(mm.)
S11 dB.
BWr%
BWc%
Lg=28mm.
12.04
14.2
13.38
-33.97
16%
16%
Lg =20mm.
17.77
30
18.83
-18.77
-
-
4
7
5.08
-16.07
59%
54%
8.95
12.15
10.76
-17.69
29%
30%
13
17
14.84
-16.85
26%
26%
Lg =10.5mm.
3.56
5.6
4.20
-25.53
48%
44%
Lg =8mm.
3.15
4.2
3.62
-19.80
29%
28%
Lg =12mm.
3.4.3 Design and Performance of CMSP Antenna with DGS and Notches In this case, we make some modifications to improve the bandwidth by using notches at different locations (center, right and left notch) when the patch radius is 9mm, but we noted that the center notch shifted (2mm) to the right side of the antenna, these structures are illustrate in (Figs. 3.31) and modifications are described in (Tab. 3.19) for antennas No.1, No.2 and No.3.
67
CHAPTER THREE
RESULTS AND DISCUSSION
(a) CMSPA with 1notches.
(b) CMSPA with 2notches.
Antenna No.1
Antenna No.2
(c) CMSPA with 3notches. Antenna No.3
Figures 3.31: Structure of CMSP antennas with DGS and notches.
Table 3.19: CMSP antennas with different notch cases. Antennas Antenna No.1 DGS+1Notch Antenna No.2 DGS+2Notches Antenna No.3 DGS+3Notches
The return loss versus frequency of these antennas are given in (Fig. 3.32) and (Tab. 3.20).
68
CHAPTER THREE
RESULTS AND DISCUSSION
-----DGS+1Notch -----DGS+2Notches -----DGS+3Notches
Figure 3.32: Characteristics of
versus Frequency for CMSP antenna with DGS and with
different notches cases.
Table 3.20: Parameters of CMSP antenna with DGS and with different notch cases. DGS with notch
S11 dB.
BWr %
BWc%
Antenna No.1 DGS+1 Notch
3.42
15.12
4.2060
-22.91
278%
126%
Antenna No.2 DGS+2 Notches
3.4
15.5
4.06
-23.35
298%
128%
Antenna No.3 DGS+3 Notches
3.31
16.13
4.05
-25.22
315%
131%
It is clear that the performance of the antenna No.3 (CMSP antenna with DGS and 3notches) is better than the others in term of impedance bandwidth and S11. The surface current distribution on the circular patch at the resonance frequency (4.05 GHz) is plotted in (Figs. 3.33).
69
CHAPTER THREE
RESULTS AND DISCUSSION
Figure 3.33: Surface current distributions on CMSP antenna.
(Fig. 3.34) and (Fig. 3.35) shows the simulated 3D gain and directivity at resonant frequency 4.05GHz of CMSP antenna with perfect ground plane (before modifications) and with CMSP antenna with DGS and 3notches. It is noted that this antenna gives omnidirectional properties.
(a) CMSPA without modifications
(b) CMSPA with DGS and 3notches.
Figure 3.34: 3D Polar plot of CMSP for Antenna Gain at resonance frequency 4.05 GHz.
70
CHAPTER THREE
RESULTS AND DISCUSSION
(a) CMSPA without modifications
(b) CMSPA with
DGS and 3notches.
Figure 3.35: 3D Polar plot of CMSP for antenna directivity at resonance frequency 4.05 GHz.
From (Fig. 3.36), we can see that the 2D radiation pattern of E – plane (phi = 0 deg) and H-plane (phi = 90 deg). 2D Radiation Pattern of DGS with three notch CMSP antenna.
Patch_Antenna_ADKv1
ANSOFT
0 -30
30 1.20 -1.60
-60
60 -4.40 -7.20
-90
90
----- E-Plane -120
120
-150
----- H-Plane
150 -180
Figure 3.36: 2D Radiation pattern of CMSP antenna for E-plane and H-plane at resonance frequency 4.05 GHz.
Meanwhile, VSWR characteristics are shown in (Fig. 3.37). It shows a satisfying outcome at frequency of 4.05 GHz (VSWR=1.11).
71
CHAPTER THREE
RESULTS AND DISCUSSION VSWR of DGS with three notch CMSP antenna.
Patch_Antenna_ADKv1
ANSOFT
5.00 4.50 Name CurveXInfo Y VSWR 4.0526 1.1159
4.00
VSWR
3.50 3.00 2.50 2.00 1.50 VSWR
1.00
0.00
5.00
10.00
15.00 Freq [GHz]
20.00
25.00
30.00
Figure 3.37: VSWR of CMSP antennas with DGS and 3notches.
3.5 Effect of Substrate Relative Permittivity on Antenna Bandwidth
Dielectric substrate plays a vital role in antenna design, primarily for giving mechanical strength to antenna. The energy storage effect of substrate is also responsible for degraded electrical properties of antenna. There are numerous substrates that can be used for the design of microstrip antennas with their dielectric constants usually in the range of [5]. The surface of the substrate has to be smooth to reduce losses and adhere well to the metal used.
In this investigation, three types of material: Duroid ( =2.2), FR-epoxy( =4.4), Rogers TMM10 ( =9.2) are used, the properties of these materials illustrated in (Tab. 2.1) (Fig. 3.38) shows the return loss characteristics of square patch antenna for different substrate materials (Duroid, FR-epoxy and RogrersTMM10). The resonant frequency decreases when the relative permittivity is increased as illustrated in (Tab. 3.21). In addition to that, the bandwidth of microstrip patch antenna decreases as a result of increasing relative permittivity
. The percentage impedance bandwidths of square patch
with respect to center frequency are 134%, 27% and 22%, when increasing relative permittivity from 2.2, 4.4 and 9.2, respectively
72
CHAPTER THREE
RESULTS AND DISCUSSION
----- Duroid ----- Epoxy ----- Rogers TMM10
Figure 3.38: Characteristics of S11 versus frequency for SMSP antenna and with various substrate material relative permittivities.
Table 3.21: Resonance frequencies, substrate permittivity, BW and S11 of SMSP antenna with different materials. Materials
BWr%
BWc%
Duroid
2.2
4.06
-19.35
345%
134%
FR-epoxy
4.4
3.47
-40.69
28%
27%
RogersTM10
9.2
2.89
-27
20%
22%
73
CHAPTER THREE
RESULTS AND DISCUSSION
3.6 General Results and Discussion I had design three different patch shapes square, triangular/rectangular and circular, for wideband applications. In this section we chose the optimum results of patch shapes (SMSPA with DGS and 3notches, T/RMSPA with DGS and one notch and CMSPA with DGS and 3notches) printed on a substrate (Duroid) have relative permittivity (2.2), thickness of (h=1.5748mm) and dimensions
. The radiating patch on the
top side of the substrate, the ground plane was placed partially (DGS) on the opposite side of the substrate has the dimensions
. All microstrip patch simulated by
software name HFSS which basis on finite element method. A series of parameters of the microstrip patch antenna should be carefully selected. In this section, the effects of several key parameters on the proposed antennas were discussed and simulated using the Ansoft HFSS In the process of analysis, it is also found that in comparison with the DGS and the substrate relative permittivity effects on the bandwidth and resonant frequency. The resonant frequency slightly decreases and bandwidth increase with decreasing ground plane length Lg. To meet these improvements, we go to the following points.
3.6.1 Bandwidth Comparisons for Different Patch Shapes
An extensive-simulation study has been carried out to determine the optimal dimensions of the square, triangular/rectangular and circular patch shapes, by maximizing the bandwidth and results are shown in (Fig. 3.39). The improvement of bandwidth, resonance frequency, returns loss, gain, directivity, efficiency and VSWR are illustrated in (Tab. 3.22). The largest improvement is provided by the DGS with 3notches, 1noatch and 3notches for square, triangular/rectangular and circular patches respectively.
74
CHAPTER THREE
RESULTS AND DISCUSSION
----- Square ----- Triangular/Rectangular ----- Circular
Figure 4.39: Comparision between the variation of S 11 versus frequency for optimum results of square, triangular/rectangular and circular patches.
Table 3.22: Comparisons between the square, triangular/rectangular and circular MSPA Parameters with DGS and notches for optimum results. S11
Patch shapes Square Triangular/ Rectangular
Circular
G
D
(dB)
(dB)
VSWR
efficie
BWr
BWc
ncy
%
%
4.06
-19.35
2.8966
2.8982
1.24
99%
345%
134%
4.49
-29.61
3.0756
3.0792
1.06
99%
276%
145%
4.05
-25.22
2.8507
2.8577
1.11
99%
315%
131%
, Total size=
3.6.2 Antenna Size Reduction (Fig. 3.40) shows the simulated return loss versus frequency for the proposed square patch antennas without DGS. As it can be seen in this figures, the first antenna (antenna No.1) operates at resonant frequency of 14.26 GHz (is the same SMSPA without modifications), but when the all dimensions of antenna No.1 are divided by 2 making antenna No.2, for examlpe the patch dimentions
75
after divided by
CHAPTER THREE
RESULTS AND DISCUSSION
2, then the dimentions equal to
and so on, the antenna No.2 can
operate at 28.27 GHz or the resonant frequency of antenna No.2 becomes the double of that of antenna No.1. While if all the dimensions of antenna No.1 are divided by a factor 4 making antenna No.3, then
its resonannt
frequency is 57.21 GHz or the resonant
frequency of antenna No.3 becomes four times that of antenna No.1 . uare patch antennas without DGS (normal, divide by 2 and divide
----- No.1 ----- No.2 ----- No.3
Figure 3.40: S11of SMSP antennas without DGS (Length Reduction) for antenna No.1,No.2 and No.3.
The use of DGS in the design of antennas No.1 , No.2 and No.3 leads to frequency shift in resonant frequency from 14.26 GHz, 28.27 GHz and 57.21 GHz to 4.2 GHz, 8.7 GHz and 17.7 GHz respectively as illustrated in (Fig. 3.41).
Lg = 10.5mm. (No.1)+DGS Lg = 5.25mm. (No.2)+DGS Lg = 2.625mm.(No.3)+DGS
Figure 3.41: S11 versus frequency of SMSP antennas with DGS (Length Reduction) for antenna No.1, No.2 and No.3.
76
CHAPTER THREE
RESULTS AND DISCUSSION
Now, it is clear that the antenna No.1 with DGS largest dimensions (substrate dimensions) are 30x28 mm2 can operate at resonant frequency of 4.2 GHz while the largest dimensions of the normal design of a square patch antenna with normal ground (without DGS) operating at the same resonant frequency of 4.2 GHz are 103x50 mm2, therefore, a size reduction of 83.5% is obtained. For the other antenna types, also a size reduction is achieved as shown in (Tab. 3.23).
Table 3.23: Size reduction of MSP antennas at difference patch shapes. Antennas
Size Ground
Square
Tria./Rect.
Circular
4.20
-
98 × 52
14.26
4.2
30 × 10.5
4.49
-
25.94
4.49
4.20
-
13.38
4.2
94.75
30
30 × 28
83.5% 0%
30× 28
82.5% 0%
52 10.5
reductions
0%
50.3
30× 10.5 98
Substrate
30 28
83.5%
3.6.3 Relationship of Resonance Frequencies with and Without DGS It is observed that the use of DGS in antennas design led to broadens the antenna bandwidth and also shifts the resonant frequency to a lower value as indicated in (Tab. 3.24) for different patch shapes.
77
CHAPTER THREE
RESULTS AND DISCUSSION
Table 3.24: Frequency shift in
for different patch shapes with and without DGS.
Antennas
BWc% before DGS
BWc% after DGS
Square : No.1
14.26
4.20
3.39
10.5%
104%
No.2
28.27
8.7
3.24
25%
112%
No.3
58.21
17.74
3.28
25%
106%
Tri./Rec.
25.94
4.49
5.96
-
111%
Circular
13.38
4.2
3.18
16%
44%
From the simulated results, the relationship of resonant frequencies with and without DGS can be expressed as:
For square and circular patches
(3.1)
While for triangular/rectangular patch
(3.2)
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CHAPTER FIVE
CONCLUSIONS AND FUTURE WORK
CHAPTER FOUR
CONCLUSIONS AND FUTURE SUGGESTIONS
4.1 Conclusions From the thesis results, it can be concluded that:
(a) the use of DGS leads to broaden the bandwidth BWc (with respect to center frequency) from 10.5% to 134%(3.42-17.45)GHz for square patch, to 145%(2.3314.63)GHz for triangular/rectangular patch and from 16% to 131%(3.3116.13)GHz for circular patch (equation 2.6).
(b) the resonant frequency is shifted by a ratio of 3.3 to a lower value for square and circular patch shapes ( equation 3.1) and about 6 for triangular-rectangular patch shape(equation 3.2).
(c) the size reduction is achieved of about 83.5% for square and circular patches and 82.5% for triangular/rectangular patches. (d) the antenna gain decreases from (6.93dB, 7.31dB and 6.24dB) to (2.8966dB, 3.0756dB and 2.8507) for square, triangular/rectangular and circular patches, respectively.
(e) the antenna directivity also falls from (6.93dB, 7.32 and 6.27) to (2.8982dB, 3.0792dB and 2.8577dB) for square, triangular/rectangular and circular patches, respectively.
79
CHAPTER FIVE
CONCLUSIONS AND FUTURE WORK
(f) the antenna efficiency reaches 99% for square, triangular/rectangular and circular patches.
(g) the VSWR of the optimum patch antennas values are 1.24, 1.06 and 1.11 for square, triangular/rectangular and circular patches respectively; this is due to good matching between transmission line and antenna.
(h) the effect of dielectric substrate permittivity is also studied in this thesis. The increment of substrate dielectric constant in antenna design results in the degradation of antenna performance such as decreasing in bandwidth with increasing dielectric permittivity frequencies with increasing
and falls to lower values of the resonance
.
4.2 Future Suggestions
Based on the previous conclusions and the limitations of the presented work, future suggestions can be carried out in the following areas:
at present facility for fabrication of patch antennas is not available in our university; the same work will be performed later. The simulated, optimized and experimental results will be compared.
as has been shown for all antennas, the work was concentrated on how to improve the impedance bandwidth. So, the future work may have its gain improved; when using DGS and array, in order to enhance the quality of the communication link and improve channel capacity and range, additional work will
need to be executed increase the antenna gain when using DGS and array.
another area for future work is to extend this concept to a multiband design. It is envisioned in the future.
80
CHAPTER FIVE
CONCLUSIONS AND FUTURE WORK
microstrip transmission line was used as feed line, other feeding techniques like, coaxial cable, Aperture-coupled feed and, Proximity Coupled Feed may be used.
81
Dedication
I would like to dedicate my thesis to: my beloved parents, my wonderful wife, and my son Nza.
Examining Committee Certification We certify that we have read this thesis entitled "Bandwidth Improvement and Size Reduction of Microstrip Patch Antenna Using HFSS" prepared by (Dana Saeed Muhammad), and as Examining Committee, examined the student in its contents and in what is connected with it, and in our opinion it meets the basic requirements toward the degree of Master of Science in Physics "Electromagnetics".
Signature: Name: Dr. Aras Saeed Mahmood Address: University of Sulaimani Title: Assistant Professor (Chairman) Date:
Signature: Name: Dr. Star Osman Hassan Address: Arbil Technology Institude Title: Assistant Professor (Member) Date: 29 / 6 / 2014
29 / 6 / 2014
Signature: Name:Dr. Asaad Mubdir Jasim Address: Sulaimani Technical College Title: Assistant Professor (Supervisor)
Signature: Name: Dr. Mati Naji Saeed Address: University of Sulaimani Title: Lecture (Member) Date:
Date: 29 / 6 / 2014
29 / 6 / 2014
Approved by the dean of the Faculty of Science and Science Education.
Signature: Name: Dr. Bakhtiar Qader Aziz Title: Professor Date: / / 2014 ii
Supervisor Certification I certify that the preparation of thesis title "Bandwidth Improvement and Size Reduction of Microstrip Patch Antenna Using HFSS" accomplished by (Dana Saeed Muhammad), was prepared under my supervisor in the School of Science, Faculty of Science and Science Education at the University of Sulaimani, as a partial fulfillment of the requirements for the degree of Master of Science in (Physics).
Signature: …………………. Name: Dr. Asaad Mubdir Jasim Title: Assistance Professor Date:
/
/2014
In view of the available recommendation, I forward this thesis for debate by the examining committee.
Signature: …………………. Name: Dr.Dana Abdulla Tahir Title: Assistance Professor Date:
/
/2014
iii
Linguistic Evaluation Certification I hereby certify that this thesis titled "Bandwidth Improvement and Size Reduction of Microstrip Patch Antenna Using HFSS" prepared by (Dana Saeed Muhammad), has been read and checked and after indicating all the grammatical and spelling mistakes, the thesis was given again to the candidate to make the adequate corrections. After the second reading, I found that the candidate corrected the indicated mistakes. Therefore, I certify that this thesis is free from mistakes.
Signature: Name: Dr. Zanyar Fa'iq Sa'eed Position: English Department. School of Languages, University of Sulaimani Date:
iv
20 / 4 /2014
Dedication I would like to dedicate my thesis to: my beloved parents, my wonderful wife, and my son, Nza.
v
Linguistic Evaluation Certification I hereby certify that this thesis titled "Bandwidth Improvement and Size Reduction of Microstrip Patch Antenna Using HFSS" prepared by (Dana Saeed Muhammad), has been read and checked and after indicating all the grammatical and spelling mistakes, the thesis was given again to the candidate to make the adequate corrections. After the second reading, I found that the candidate corrected the indicated mistakes. Therefore, I certify that this thesis is free from mistakes.
Signature: Name: Dr. Zanyar Fa'iq Sa'eed Position: English Department. School of Languages, University of Sulaimani Date:
20 / 4 /2014
