two element printed mimo antennas for wireless...
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TWO ELEMENT PRINTED MIMO ANTENNAS FOR
WIRELESS APPLICATIONS
WAN NOOR NAJWA BINTI WAN MARZUDI
UNIVERSITI TUN HUSSEIN ONN MALAYSIA
TWO ELEMENT PRINTED MIMO ANTENNAS FOR WIRELESS
APPLICATIONS
WAN NOOR NAJWA BINTI WAN MARZUDI
A thesis submitted in fulfilment of the requirement for the award of the Degree of
Master of Electrical Engineering
Faculty of Electrical and Electronic Engineering
Universiti Tun Hussein Onn Malaysia
MARCH 2016
iv
To my beloved parents, Wan Marzudi Wan Omar and Azizah
Yunus and beloved siblings,
Wan Noor Marniza and Wan Mohd Azreen
for their motivation and inspiration.
To all those who believe in the richness of learning.
v
ACKNOWLEDGEMENT
First of all, Alhamdulillah. I am so grateful to Allah S.W.T for giving me the strength
and guidance throughout my studies. Again, thank you Allah for easing my path
towards understanding a part of Your vast knowledge.
I would like to express my deepest and sincere gratitude to my supervisor Dr.
Zuhairiah Zainal Abidin for her excellent guidance, supervision and support that
helped me a lot in completing this thesis.
Special thanks to Encik Mohd Rostam Anuar and Puan Miskiah Muhamad
Ihsan for their guidance and assistance during my measurement works conducted in
the EMCentre at Universiti Tun Hussein Onn Malaysia (UTHM). Thanks to all
Project Lab technicians who had contributed to the succesful completion of this
project.
I would like to express my sincere gratitude to Kementerian Pengajian
Malaysia (KPM) for funding this work through “Geran Insentif Penyelidik Siswazah
(GIPS)”.
Last but not least, I would like to give my big thanks to my parents, siblings
and friends for their support, love and patience. Without their encouragement,
motivation and understanding it would have been impossible for me to complete this
work.
vi
ABSTRACT
Multiple Input Multiple Output (MIMO) technology is a promising approach to fulfil
the demand of current wireless systems that requires higher data rate and larger
capacity in a compact size. The main challenge in designing a MIMO antenna in a
close packed space is to achieve high isolation between the antenna elements. This
research study concentrates on the design and analysis of several small sized two -
elements MIMO antennas that have a working frequency for the following
applications, such as Bluetooth (2.4 GHz), LTE2300 (2.3 – 2.4 GHz), LTE2600 (2.5-
2.69 GHz), Wi-Fi (2.4 – 2.485 GHz), WLAN (2.4/5.2/5.8 GHz) and WiMAX
(2.5/3.5/5.5 GHz). The proposed design were analysed with a different set of
parameters. The aforementioned antennas are design by means of different methods
that includes neutralization line technique, stub and defected ground plane to
suppress the mutual coupling. The MIMO parameters such as mutual coupling,
envelope correlation coefficient, total active reflection coefficient (TARC), capacity
loss and channel capacity were investigated and analysed. All the proposed MIMO
antenna design achieved satisfactory results with a reflection coefficient less than
-10 dB, mutual coupling less than -13 dB and envelope correlation coefficient less
than 0.5. Therefore, it could be concluded that all the proposed MIMO antenna
designs demonstrated a considerable good performance and met the required
prerequisite of a MIMO antenna.
vii
ABSTRAK
Teknologi berbilang masukan dan berbilang keluaran (MIMO) adalah pendekatan
yang menjanjikan kadar data yang lebih tinggi dan keupayaan yang lebih besar
dalam saiz yang kompak untuk memenuhi permintaan semasa sistem tanpa wayar.
Cabaran utama dalam merekabentuk antena berbilang masukan dan berbilang
keluaran di dalam satu ruang yang rapat adalah untuk mencapai pengasingan tinggi
diantara elemen antena. Kajian penyelidikan ini tertumpu kepada merekabentuk dan
menganalisis beberapa antenna dua elemen berbilang masukan dan berbilang
keluaran dengan saiz yang kecil yang mempunyai kekerapan kerja untuk aplikasi
Bluetooth (2.4 GHz), LTE2300 (2.3 - 2.4 GHz), LTE2600 (2.5-2.69 GHz), Wi-Fi
(2.4-2.485 GHz), WLAN (2.4 / 5.2 / 5.8 GHz) dan WiMAX (2.5 / 3.5 / 5.5 GHz.
Reka bentuk yang dicadangkan dianalisis dengan parameter yang berbeza. Beberapa
antenna berbilang masukan dan berbilang keluaran di rekabentuk dengan
menggunakan kaedah yang berbeza termasuk peneutralan teknik talian, punting dan
struktur gangguan satah pembumian untuk menindas gandingan bersama telah
dicadangkan. Parameter berbilang masukan dan berbilang keluaran adalah seperti
gandingan bersama, pekali korelasi sampul surat, jumlah pekali pantulan aktif
(TARC), kehilangan keupayaan dan kapasiti saluran telah disiasat dan dianalisis.
Semua reka bentuk antena berbilang masukan dan berbilang keluaran yang
dicadangkan mencapai prestasi yang baik dengan pekali pantulan kurang daripada -
10 dB, gandingan bersama kurang daripada -13 dB dan pekali korelasi sampul surat
kurang daripada 0.5. Oleh itu, semua reka bentuk antena MIMO dicadangkan
menunjukkan prestasi yang baik dan memenuhi kehendak antena MIMO.
viii
TABLE OF CONTENTS
ABSTRACT vi
ABSTRAK vii
TABLE OF CONTENTS vii
LIST OF PUBLICATIONS xii
LIST OF TABLES xiv
LIST OF FIGURES xv
LIST OF SYMBOLS AND ABBREVIATIONS xxi
LIST OF APPENDICES xxii
CHAPTER 1 INTRODUCTION 1
1.1 Project Background 1
1.2 Problem Statements 4
1.3 Aims and objectives 5
1.3.1 Aims 5
1.3.2 Objectives 5
1.4 Scope of Projects 6
1.5 Thesis Organizations 6
CHAPTER 2 THEORETICAL BACKGROUND OF MIMO AND
ITS APPLICATIONS 8
2.1 Introduction 8
2.2 MIMO Antenna System 8
2.3 MIMO Antenna Parameters 10
2.3.1 Total Active Reflection Coefficient (TARC) 10
2.3.2 Correlation Coefficient 11
ix
2.3.3 Capacity Loss 11
2.3.4 Channel Capacity 12
2.3.5 Mutual Coupling and Isolation 13
2.4 Techniques to Enhance Isolation and Its Applications 13
2.4.1 Neutralization Line (NL) 13
2.4.2 Stub on the Ground Plane 19
2.4.3 Defected Ground Plane 25
2.5 Channel capacity enhancement using MIMO
Technology 29
2.6 Summary of Previous Work 30
CHAPTER 3 ANTENNA DESIGN CONCEPT 33
3.1 Introduction 33
3.2 Flow Chart 33
3.3 Design Requirement 35
3.3.1 Frequency Band 35
3.3.2 Dielectric Substrate 35
3.4 Mathematical Method 36
3.5 Single Element Antenna 37
3.5.1 Wideband G-Shaped Slotted Printed Monopole
Antenna for WLAN/WiMAX Applications 37
3.6 MIMO/Diversity Antenna 38
3.6.1 Design 1: Two Elements Crescent Shaped
Antenna 38
3.6.2 Design 2: The Effect of Meander Line Slit on Lower
Band Printed MIMO Antenna 39
3.6.3 Design 3: Compact Orthogonal Wideband Printed
MIMO Antenna for Wi-Fi/WLAN/LTE
x
Applications 40
3.6.4 Design 4: Dual Band Printed G-Shaped Slotted
MIMO Antenna for WLAN/WiMAX Applications 41
3.7 Methods for Antenna Measurements 42
3.7.1 S-Parameters Measurement 42
3.7.2 Far-Field Measurement in Anechoic Chamber 43
3.7.3 Gain Determination Using Gain Transfer Method 46
3.7.3.1 Gain Transfer Method using VNA 46
3.7.3.2 Gain Transfer Method using Spectrum
Analyzer with Separate Signal Generator 48
3.8 Summary 50
CHAPTER 4 ANTENNA PROTOTYPING , RESULTS ANALYSIS 52
4.1 Introduction 52
4.2 Single Element Antenna 52
4.2.1 Wideband G-Shaped Slotted Printed Monopole
Antenna for WLAN/WiMAX Applications 52
4.2.2 Design Summary 60
4.3 MIMO/Diversity Antenna 60
4.3.1 Design 1: Two Elements Crescent Shaped
Antenna 60
4.3.1.1 Design Summary 68
4.3.2 Design 2: The Effect of Meander Line Slit
on Lower Band
Printed MIMO Antenna 69
4.3.2.1 Design Summary 76
xi
4.3.3 Design 3: Compact Orthogonal Wideband Printed
MIMO Antenna for Wi-Fi/WLAN/LTE
Applications 76
4.3.3.1 Design Summary 86
4.3.4 Design 4: Dual Band Printed G-Shaped Slotted MIMO
Antenna for WLAN/WiMAX Applications 86
4.3.4.1 Design Summary 94
4.4 Summary 94
CHAPTER 5 CONCLUSION AND RECOMMENDATION FOR FUTURE
WORK 95
5.1 Summary of Thesis 95
5.2 Achievements and Research Contributions 96
5.3 Recommendation of Future Work 98
REFERENCES 99
APPENDICES 106
xii
LIST OF PUBLICATIONS
1. Marzudi, W.N.W and Abidin Z.Z, “Dual Wideband G-Shaped Slotted
Printed Monopole Antenna for WLAN and WiMAX Application”, RF and
Microwave Conference (RFM), 2013 IEEE International: pp. 225-227, 2013.
2. W.N.N.W.Marzudi, Z.Z.Abidin, S.Z.Muji, Ma Yue, and R.A.A.Alhameed, “
Mutual Coupling Reduction of Two Elements Antenna for Wireless
Applications”, In The Second International Conference on Technological
Advance in Electrical, Electronics and Computer Engineering
(TAEECE2014), pp 131-136, The Society of Digital Information and
Wireless Communication, 2014.
3. W.N.N.W.Marzudi, Z.Z.Abidin, S.Z.Muji, Ma Yue, and R.A.A.Alhameed, “
Minimization of Mutual Coupling Using Neutralization Line Technique for
2.4 GHz Wireless Applications”, International Journal of Digital
Information and Wireless Communicatiob (IJDIWC), Vol 4(3), pp. 26-32,
2014.
4. W.N.N.W.Marzudi, Z.Z.Abidin, S.Z.M.Muji, M.Yue and R.A.A.Alhameed,
“ Wideband G-Shaped Slotted Printed Monopole Antenna for WLAN and
WiMAX Applications”, International Journal on Electrical and
Informatics,vol.6,no.3, September 2014.
5. Wan Noor Najwa Wan Marzudi, Zuhairiah Zainal Abidin, Mohd Zarar
Mohd Jenu, Ma Yue, “The Effect of Meander Line Slit on Lower Band
Printed MIMO Antenna”, IEEE Asia Pacific Conference on Applied
Electromagnetic (APACE), pp.135-138, 2014.
6. W.N.N.W.Marzudi, Z.Z.Abidin, Ma Yue, R.A.A.Alhameed, “ Two
Elements Crescent Shaped Printed Antenna for Wireless Applications”,
Advanced Computer and Communication Engineering Technology, Lecture
Notes In Electrical Engineering,Vol 315, pp.195-203, 2015.
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7. N.N.Othman, W.N.N.W.Marzudi, N.F.M.Yusof, Z.Z.Abidin, S.Z.M.Muji
and Ma Yue, “MIMO Antenna Performance on Microstrip Antenna with
EBG Structure for WLAN Applications”, Applied Mechanics and Materials,
vol.773-774, 2015, pp.756-760.
8. W.N.N.W.Marzudi, Z.Z.Abidin, S.H.Dahlan, Ma Yue, Raed A.Abd-
Alhameed, M.B.Child, “ A Compact Orthogonal Wideband Printed MIMO
Antenna for WiFi/WLAN/LTE Applications”, Microwave and Optical
Technology Letter, Vol.6, no.7, July 2015.
xiv
LIST OF TABLE
2.1 Summary: Performances Comparison of MIMO Antenna 30
3.1 Working Frequencies band of proposed antenna 35
3.2 The Dimension for Single Element G-Shaped Slotted Antenna 38
3.3 Design parameter of the proposed antenna 41
4.1 Comparison of Antenna Performances with and without Neutralization
Line 68
5.1 Comparison of Proposed Antennas and Previous Works 97
xv
LIST OF FIGURES
1.1 Wireless Technology [2] 1
1.2 Bluetooth Technology [3] 2
1.3 Home WLAN [4] 3
1.4 WiMAX [5] 3
1.5 MIMO System 4
1.6 MIMO antenna design summary using different techniques to reduce
mutual coupling 7
2.1 Basic model of SISO, SIMO, MISO and MIMO [11] 9
2.2 MIMO System Concept 10
2.3 MIMO Capacity 12
2.4 The structure of the proposed MIMO antenna (unit: mm) [21]. 14
2.5 The simulated isolation with and without neutralizing line [21]. 14
2.6 Detailed dimensions of the proposed antenna [22]. 15
2.7 Simulated reflection coefficient and isolation of the proposed antenna.
(a) Without neutralization line; (b) With neutralization line [22]. 15
2.8 Geometry of the proposed dual-antenna with dimensions in millimeters (the
front side is in black, and the back side is in grey); (a) Perspective view. (b)
Front view. (c) Bottom view (metal on the front is omitted) [23]. 16
2.9 Simulated S-parameters with and without three neutralization lines.
(a) S11; (b) S21 [23]. 16
2.10 Isolation level with and without neutralization line [24]. 17
2.11 Simulated and measured envelope correlation coefficient (ECC) [24]. 17
2.12 Geometry of the proposed antenna [25]. 18
2.13 Geometry of the proposed antenna [26]. 18
2.14 Simulated S11 and S21 for the proposed antenna (the proposed dual antenna)
the case with the F-like monopole (dual-ant 1), the dual-ant without NL
xvi
(dual-ant 2) and the dual-antenna without match branch (dual-ant 3) [27]. 19
2.15 Geometry of the proposed antenna [28]. 20
2.16 Geometry of the proposed antenna [29]. 21
2.17 Simulated S-Parameters for single element antenna with and without
Long ground stubs [29] 21
2.18 Geometry of the proposed antenna [30] 22
2.19 Simulated S-Parameters of proposed antenna with and without
Decoupling structure (a) S11; (b)S21 [30] 22
2.20 Geometry of the proposed antenna [33] 23
2.21 Simulated and measured S-Parameters. (a) S11 and (b) S21[33]. 23
2.22 Geometry of the proposed diversity antenna [34]. 24
2.23 Geometry of the proposed MIMO antenna array [35]. 24
2.24 S-parameter characteristic of the proposed antenna [35]. 24
2.25 Geometry of the proposed antenna [37]. 26
2.26 Simulated S-parameter [37]. 26
2.27 Configuration of the proposed antenna [38]. 27
2.28 Simulated scattering parameters [38]. 27
2.29 Antenna configurations [39]. 28
2.30 Simulated S-parameters characteristics [39]. 28
2.31 Simulated S-parameters with and without ground slits [41]. 29
3.1 Flowchart of Antenna Production 34
3.2 Configuration of the proposed Single Element Antenna 37
3.3 Configuration of the proposed MIMO Antenna Design. (a) Front View;
(b) Back View 38
3.4 Configuration of the proposed antenna; (a) Reference Antenna ( without
L-stub, semi-circular slot and meander line); (b) Proposed antenna (with
L-stub, semi-circle slot and meander line); (c) Meander slit
configuration (in mm) 40
3.5 Configuration of the proposed antenna. (a) Front view; (b) back view;
(c) patch view and (d) slot views 41
3.6 Configuration of the proposed antenna. (a) Front view; (b) Back view 42
3.7 Antenna Measurement for S11 result 43
3.8 Antenna measurement for S21 result 43
3.9 Far-filed anechoic chamber measurement 44
xvii
3.10 Linear position in vertical and horizontal direction 45
3.11 Antenna under test terminated with 50Ω load 45
3.12 Example of measured radiation pattern result. (a) Linear position in vertical.
(b) Linear position in horizontal. 46
3.13 Photograph of normalized S21 47
3.14 Replaced Reference antenna with AUT for relative gain measurement 48
3.15 Horn antenna as transmitting and receiving antenna 49
3.16 Measurement setup to obtain power receives of reference antenna 49
3.17 Power received, PR2 of AUT measured 50
4.1 Simulated Return Loss. (a) with various dimensions of Ws; (b) with
various dimensions of Ls 53
4.2 Simulated Surface Current Distribution of the Proposed G-Shaped
Slotted Antenna at; (a) 2.4 GHz; (b) 2.5 GHz; (c) 3.5 GHz; (d) 5.2 GHz;
(e) 5.5 GHz; and (f) 5.8 GHz 54
4.3 Simulated return loss. (a) with various dimensions of Wd; (b) with
various dimensions of Ld 55
4.4 Comparison of Return Loss, S11 with and without defected ground
Plane 56
4.5 Practical prototype of the proposed antenna design 57
4.6 Simulated and measured return loss of the proposed antenna 57
4.7 Simulated and measured VSWR of the proposed antenna 57
4.8 Simulated radiation pattern of the proposed antenna at 2.4, 2.5, 3.5, 5.2,
5.5 and 5.8 GHz in the x-z Plane. "xxxx" Simulated cross-polarization,
"oooo" simulated co-polarization 58
4.9 Simulated radiation pattern of the proposed antenna at 2.4, 2.5, 3.5, 5.2,
5.5 and 5.8 GHz in the y-z Plane. "xxxx" Simulated cross-polarization,
"oooo" simulated co-polarization 59
4.10 Antenna gain 59
4.11 Simulated Transmission Coefficient, S21 of the various distance location
of neutralization line 61
4.12 The practical prototype of the proposed MIMO antenna 61
4.13 Comparative plot S-Parameters output for simulated and measured result
for the proposed antenna with neutralization line 62
xviii
4.14 Contour plot surface current distributions (a) with; (b) without neutralization
line at 2.4 GHz. Port 1 (left) is excited, and port 2 (right) is terminated in
50Ω. 63
4.15 Simulated capacity loss of the proposed antenna with and without
neutralization line 64
4.16 Simulated TARC of the proposed antenna with and without
neutralization line 64
4.17 Comparative plot envelope correlations output for simulated and
measured results for the proposed antenna with neutralization line 64
4.18 Comparison between simulated and measured capacity loss of the
proposed antenna 65
4.19 Comparison between simulated and measured TARC of the
proposed antenna 65
4.20 Simulated capacity of the proposed antenna with and without neutralization
line 65
4.21 Measured radiation pattern of the proposed antenna at 2.4,
GHz in the XZ-Plane and YZ plane. "xxxx" Simulated cross-
polarization "oooo" simulated co-polarization 66
4.22 Antenna gain without neutralization line at 2.4 GHz 67
4.23 Antenna gain with neutralization line at 2.4 GHz 67
4.24 The development of U-slit from zero to fifth iteration 69
4.25 Changes in S11 by increased number of iteration 69
4.26 Changes in S-Parameters with different number of meander slits etched
on the patch 70
4.27 Changes in S-Parameters with and without semi-circle slot 70
4.28 Practical prototype of the proposed antenna 71
4.29 Comparison of S-Parameters between reference and proposed antenna 71
4.30 Contour plot surface current distribution without (top) and with (bottom) L-
stub at (a) 2.5 GHz; (b) 3.5 GHz; and (c) 5.8 GHz. Port 1 (left) is excited and
port 2 (right) is terminated in 50Ω 72
4.31 Comparison of S-Parameters between simulated and measured results 72
4.32 Envelope correlation coefficient of the proposed antenna 73
4.33 Simulated capacity loss and TARC of the proposed antenna 73
xix
4.34 Simulated radiation patterns of the proposed antenna for two planes [(left) x-z
plane, (right) y-z plane] at (a) 3.5 GHz, (b) 5.2 GHz, (c) 5.5 GHz,and (d) 5.8
GHz). Port 1 is excited and port 2 is terminated in 50Ω”oooo” simulated co-
polarization, “xxxx” simulated cross-polarization. 74
4.35 Simulated antenna gain of the proposed antenna at (a) 3.5 GHz, (b) 5.2 GHz,
(c) 5.5 GHz and (d) 5.8 GHz. 75
4.36 Simulated capacity of the proposed antenna. 76
4.37 Simulated S-Parameters of the proposed antenna with and without T
Slot 77
4.38 Simulated S-Parameters of the proposed antenna with and without L-
Shaped Stub 78
4.39 Simulated S-Parameters of the proposed antenna with and without
Rectangular slot 78
4.40 The current distribution at 2.4 GHz. (a) without rectangular slot; (b)
with rectangular slot. 79
4.41 The simulated S-Parameters with various Ws3. (a) Return loss; (b)
Mutual coupling 79
4.42 Practical prototype of the proposed antenna 80
4.43 Simulated and measured S-Parameters. (a) S11,S22; (b) S12,S21 81
4.44 Measured envelope correlation coefficient of the proposed antenna 81
4.45 Simulated and measured capacity loss of the proposed antenna
design 82
4.46 Simulated and measured TARC of the proposed antenna
design 83
4.47 Simulated and measured VSWR of the proposed antenna design 83
4.48 Antenna gain 83
4.49 Simulated and measured normalized radiation patterns of the proposed
antenna for two planes [(left) x-z plane, (right) y-z plane] at (a) 2.4 GHz,
(b) 3.5 GHz, (c) 5.2 GHz,and (d) 5.5 GHz). Port 1 is excited and port 2
is terminated in 50Ω”oooo” measured co-polarization, “xxxx” measured
cross-polarization, “----” simulated co-polarization, “- - - -” simulated cross-
polarization 84
4.50 Simulated and measured normalized radiation patterns of the proposed
antenna for two planes [(left) x-z plane, (right) y-z plane] at (a) 2.4 GHz,
xx
(b) 3.5 GHz, (c) 5.2 GHz,and (d) 5.5 GHz). Port 2 is excited and port 1
is terminated in 50Ω”oooo” measured co-polarization, “xxxx” measured
cross-polarization, “----” simulated co-polarization, “- - - -” simulated cross-
polarization 85
4.51 Simulated capacity of the proposed antenna design. 86
4.52 Simulated S-Parameters with and without rectangular slots 87
4.53 Simulated S-Parameters with and without neutralization line 87
4.54 Simulated S-Parameters with and without rectangular slots 88
4.55 Simulated S-Parameters with and without stub 88
4.56 Prototype of the proposed antenna design 89
4.57 Simulated S-Parameters. (a) Reflection Coefficient, S11; (b) Transmission
Coefficient, S21 90
4.58 Measured envelope correlation coefficient 90
4.59 Comparison between simulated and measured result. (a) Capacity loss
(b) TARC 91
4.60 Simulated and measured radiation patterns of the proposed antenna for two
planes [(left) x-z plane and (right) y-z plane] at (a) 2.4 GHz, (b) 3.5 GHz, (c)
5.5 GHz and (d) 5.8 GHz . Port 1 is excited, and port 2 is terminated. “____”
simulated co-polarization, “_ _ _” simulated cross-polarization, „oooo‟
measured co-polarization and “xxxx” measured cross-polarization 92
4.61 Comparison between simulated and measured proposed antenna gain 93
4.62 Simulated capacity of the proposed antenna design. 93
xxi
LIST OF SYMBOLS AND ABBREVIATIONS
% Percentage
BER Bit Error Rate
CST Computer Simulation Technology
dB Decibel
DGS Defected Ground Structure
EBG Electromagnetic Band Gap
GHz Giga Hertz
GSM Global System for Mobile
IEEE Institute of Electrical and Electronics Engineers
LTE Long Term Evolution
MIMO Multiple Input Multiple Output
MISO Multiple Input Single Output
Rx Receiver
S11 Return Loss
S21 Mutual Coupling
SIMO Single Input Multiple Output
SISO Single Input Single Output
TARC Total Active Reflection Coefficient
Tx Transmitter
UMTS Universal Mobile Telecommunication System
Wi-Fi Wireless Fidelity
WiMAX Worldwide Interoperability for Microwave Access
WLAN Wireless Local Area Network
xxii
LIST OF APPENDICES
A Dual Wideband G-Shaped Slotted Printed Monopole Antenna for WLAN
and WiMAX Applications 107
B Mutual Coupling Reduction of Two Elements Antenna for Wireless
Applications 108
C Minimization of Mutual Coupling Using Neutralization Line Technique for
2.4 GHz Wireless Applications envelope correlation coefficient 109
D Wideband G-Shaped Slotted Printed Monopole Antenna for WLAN and
WiMAX Applications 110
E The Effect of Meander Line Slit on Lower Band Printed MIMO
Antenna 111
F MIMO Antenna Performance on Microstrip Antenna with EBG Structure
for WLAN Applications. 112
G Two Elements Crescent Shaped Printed Antenna for Wireless
Applications 113
H A Compact Orthogonal Wideband Printed MIMO Antenna
for WiFi/WLAN/LTE Applications 114
1
CHAPTER 1
INTRODUCTION
1.1 Project Background
Over the past few decades, wireless communication has been given due attention in
the field of communications. Its rapid growth is owed to the increasing demand for
tether less connectivity apart from the advancement of VLSI technology and the
success of second generation (2G) digital wireless standards [1]. In essence, wireless
communication is defined as the transmission of data without the use of wires [2].
The application of such technology is evident through its implementation, for
instance in Bluetooth, Ultra-Wide Band, satellite, cellular, wireless LAN, Wi-Fi and
WiMAX technologies. Figure 1.1 illustrates the wireless technology from the access
point to the devices.
Figure 1.1: Wireless Technology [2].
2
Bluetooth is a wireless standard design for short range wireless
communication technology. The purpose of Bluetooth design is to eliminate cable
connection between devices such as the computer, allowing for synchronisation
between printers, mobile, etc. The nearby devices will connect at Bluetooth
technology at data rate 1 Mbps. Devices that use such technology is depicted in
Figure 1.2.
Figure 1.2: Bluetooth technology [3].
Other than Bluetooth technology, the introduction of wireless network for
internet communication also has gained popularity through the introduction of Wi-Fi
or wireless fidelity and the wireless local area network (WLAN). A WLAN is an
extension of a wired LAN that connects through a wireless access point. WLANs
operate based on networking standards established by the Institute of Electrical and
Electronic Engineers (IEEE). The IEEE published a series of standards, namely
IEEE.802.11a, IEEE.802.11b, and IEEE.802.11g, that varies with respect to their
data transmission speed and distance. According to the aforementioned standards,
WLANs can transmit at a speed from 11 Mbps to 54 Mbps [2]. Conversely, the
worldwide interoperability for microwave access (WiMAX) that is also known as
IEEE.802.16 is a type of wireless technology that provides wireless internet service
over a longer distance as compared to the standard Wi-Fi. WiMAX provides
broadband wireless access to up to 30 miles and uses fixed and mobile stations to
provide users with access to high-speed voice, data, and internet connectivity.
3
Applications of WLAN and WiMAX is shown in Figure 1.3 and Figure 1.4,
respectively.
Figure 1.3: Home WLAN [4].
Figure 1.4: WiMAX [5].
In wireless communication system, there is a significant demand for higher
data rate as well as a larger bandwidth antenna at both transmitter and receiver. This
is where the utilisation of antenna plays a vital role. More than one antenna is
required for wireless communication terminals to reach higher data rate. MIMO
technology has received considerable attention over the years. Figure 1.5 illustrates
MIMO antenna system. MIMO technology that utilises multiple antennas for both at
4
the transmitting and receiving end of the communication system is considered as one
of the promising approaches to reach higher data rate in rich scattering environment
[6-8]. MIMO technology exploits multipath to provide higher data throughput and
simultaneously increases the range and reliability without consuming extra radio
frequency. MIMO can be implemented by means of beamforming, spatial
multiplexing and diversity techniques [8]. Through the introduction of multiple
antennas at both transmitter and receiver side, the diversity is achievable. The
channel capacity, bandwidth and data rate increases naturally without increasing the
transmitting power signal. The MIMO system is shown in Figure 1.5.
Figure 1.5: MIMO system.
1.2 Problem Statement
The rapid growth in wireless communication technology has led to the development
of wideband antennas and an increasing need for having higher data rate for data
signal transmission. One of the means to address this issue is by increasing the
number of antennas at the wireless communication terminals. Multiple Input and
Multiple Output (MIMO) technology has been given attention over the years as it
could provide higher data rate in rich scattering environment by having multiple
antennas. A major consideration in MIMO antenna design is to reduce correlation
between the multiple elements and in particular the mutual coupling electromagnetic
interactions that exist between multiple elements are significant. Too high mutual
5
coupling will increase the signal correlation between the channels and decrease the
antenna radiation efficiency [9]. It seems obvious that lower mutual coupling will be
ensured if the two radiating elements are spaced as far as possible. However, to
integrate multiple antennas closely in a small and compact device while maintaining
a minimum distance of 0.5λ between radiating element [10] and achieve lower
mutual coupling between antennas element is a challenging task.
Requirements for various techniques of isolation and mutual coupling
improvement for MIMO applications are constantly growing. With the rapid
development of wireless applications such as Bluetooth, WLAN, WiMAX, Wi-Fi
and LTE terminal devices, the needs to enhance the system performance and
compact antenna size have gained a lot of attention. Therefore, the design of MIMO
antenna for wireless applications carried out in this study to improve an antenna size
with lower mutual coupling less than -10 dB with minimum separated distance
between antenna elements less than 0.5λ at 2.4 GHz and good MIMO characteristics
is proposed and investigated. This study presents a number of novel wideband
printed compact MIMO antennas for wireless applications.
1.3 Aims and objectives
1.3.1 Aims
This study aims at improving the size and performance of MIMO antenna system
through the development and implementation of a wideband printed MIMO antennas
for wireless applications. The improvements in terms of mutual coupling, envelope
correlation coefficient, channel capacity, total active reflection coefficient (TARC)
and capacity loss between elements are investigated.
1.3.2 Objectives
The objectives of this study are as follows:
1. To design, model and implement several printed MIMO antennas for
wireless communication.
2. To investigate and analyze the performance of the MIMO antenna system.
6
1.4 Project Scope
The limitations of this research are:
1. Design and fabricate several two element MIMO wideband antennas
working on wireless applications such as LTE2300 (2300-2400 MHz),
LTE2600 (2500 – 2690 MHz), (Bluetooth (2.4 GHz), WLAN (2.4/5.2/5.8
GHz), WiMAX (2.5/3.5/5.5 GHz).
2. Design several two element MIMO antennas using three different techniques
to reduce mutual coupling which are neutralization line, stub structure and
defected ground plane.
3. Investigate the performance of MIMO criteria in terms of correlation
coefficient, capacity channel, total active reflection coefficient (TARC),
bandwidth, antenna gain and radiation pattern of the wideband antenna.
1.5 Thesis Organization
This thesis is organized into five chapters. Chapter 1 provides an overview of the
project that includes the project background, objectives, problem statements and
scope of the project.
Chapter 2 specifically reviews the theoretical background and previous
literature regarding the MIMO antenna. Three different techniques that can be
employed to reduce mutual coupling between antenna elements are considered.
Chapter 3 describes the details of the approach used to design the MIMO
antenna as well as the workflow for the implementation of this project. Antennas
design concept is also discussed. The measurement setup to measure S-Parameters,
radiation patterns, and the antenna gain are also explained.
Chapter 4 explains the optimization of the antennas and comparison between
the simulated and the measured performances. In this chapter, different techniques to
reduce mutual coupling are introduced. All research and published work are
discussed in detail in this chapter that includes S-Parameters, radiation patterns, and
MIMO antenna parameters. The parameters that were taken into consideration are
namely, the correlation coefficient, total active reflection coefficient (TARC),
capacity loss and channel capacity of several MIMO antennas for wireless
7
applications. The proposed MIMO antennas design using different techniques to
reduce mutual coupling are illustrated in Figure 1.6.
Figure 1.6: MIMO antenna design summary using differences technique to reduce
mutual coupling.
Finally, Chapter 5 draws the conclusion of this thesis and recommendation
for future works are also proposed in this chapter.
MIMO Antenna design
Design 1 Design 4 Design 3 Design 2
Techniques to reduce mutual coupling
Neutralization
Line (NL)
Stub
Structure
Defected
Ground Plane
NL +
Defected
Ground
Plane
FR-4
substrate
Rogers
Substrate
8
CHAPTER 2
THEORETICAL BACKGROUND OF MIMO AND ITS APPLICATIONS
2.1 Introduction
This part of the report discusses previous works conducted that are related to
different applications of MIMO antenna. Various techniques that have been
employed in the literature to achieve optimal antennas design are also reported. A
major consideration in MIMO antenna design is to reduce correlation between the
multiple elements and in particular the mutual coupling electromagnetic interactions
that exist between multiple elements are significant, because at the receiving end this
effect could largely determine the performance of the system. Lower mutual
coupling can result in higher antenna efficiencies and lower correlation coefficients
[6].
2.2 MIMO antenna system
The development of wireless communication system begins with the inception of the
single input/single output antenna system (SISO) that consists of a single antenna to
transmit the signal to the transmitter and receives the signal from a receiver. Further
development saw the birth of smart antenna system. A smart antenna system may be
categorized into a single input/multiple output (SIMO) and multiple input/single
output (MISO).
9
There is an insatiability demand for high data rate, high link quality and large
bandwidth antenna for both the transmitter as well as the receiver. These criteria may
be achieved by the inclusion of more than one antenna through MIMO technology.
The basic idea of MIMO system is to improve quality (BER) or data rate (bits/s) by
using multiple TX/RX antennas. MIMO technology using multiple antennas for both
transmitting and receiving end of the communication system is considered as one of
the most promising approaches to reach higher data rate in rich scattering
environment [6-8]. The basic notion of the SISO, SIMO, MISO and MIMO are
illustrated in Figure 2.1.
Figure 2.1: Basic model of SISO, SIMO, MISO and MIMO [11].
MIMO technology exploits multipath to provide higher data throughput and
simultaneously increase its range and reliability without consuming extra radio
frequency. MIMO can be implemented through beamforming, spatial multiplexing
and diversity techniques [12]. By introducing multiple antennas at both transmitter
and receiver side, the diversity is achievable. The channel capacity, bandwidth and
data rate increases automatically without increasing the transmitting power signal.
The MIMO concept is depicted in Figure 2.2.
Existing
Technology
Smart
Antenna
System
MIMO
System
10
Figure 2.2: The MIMO system concept.
A major challenge in designing a MIMO antenna is the mutual coupling.
Mutual coupling is the electromagnetic interaction between antenna elements due to
the small space of the antenna element. The performance of the MIMO antenna
system such as lower correlation coefficient and higher antenna efficiencies are often
influenced by low mutual coupling.
2.3 MIMO Antenna Parameters
This section reviews MIMO antenna parameters that are extended from the
traditional single element antenna parameters.
2.3.1 Total Active Reflection Coefficient (TARC)
TARC (Γ) is defined as the square root of the ratio of reflected power and incident
power, mathematically given by [12]:
=
(2.1)
For a lossless N-port antenna, the TARC can be described as:
= √
/√
(2.2)
where;
ai is the incident signal vector with randomly phased elements.
bi is the reflected signal vector.
11
Furthermore, the scattering matrix for 2×2 network can be written as;
(
) = (
) (
) (2.3)
The TARC can be computed by applying different combinations of excitation
signals to each port. The TARC value is a real number between zero and one. The
delivered power is radiated when the value of the TARC equals to zero, conversely
the power is either reflected back or goes to other ports when it is equal to one.
2.3.2 Correlation Coefficient
The correlation coefficient measures the degree of similarity amongst the received
signals. It varies from 0 to 1. Diversity systems are considered good if the correlation
coefficient of the system is zero or low by default. Ideally, the envelope correlation
coefficient (ECC) may be computed by means of; i) from far-field radiation pattern
and ii) from scattering parameters of the proposed antenna system. However,
calculating from the far field radiation pattern would require a complex and advanced
calculation.. The reason for complexity is that the correlation is actually described by
two metrics: complex and envelope correlations [13, 14]. The correlation coefficient
can be computed from S-parameters using the following equation [15]:
e=
( )( )
(2.4)
Where the terms are;
S11 = power reflected from port 1.
S12 = power transmitted from port 1 to port 2.
S21 = power transmitted from port 2 to port 1.
S22 = power reflected from port 2.
2.3.3 Capacity Loss
Theoretically, the channel capacity can be improved by increasing the number of
antennas. The capacity loss (Closs) can be calculated by using equation as follows [16
,17]
12
( ) (2.5)
Where is the receiving antenna correlation matrix given by :
[
]
With ( ( | |
)) and ( ) for i , j = 1 or 2.
2.3.4 Channel Capacity
Figure 2.3 illustrates the MIMO capacity. Multiple antennas that induces multipath
propagation at both transmitter and receiver can establish essentially multiple parallel
channels that operate simultaneously, on the same frequency band at the same total
radiated power. Channel capacity involved with the information handling capacity of
a given channel. The equation of channel capacity is given by [18]:
C= [ *
+] bits/s/Hz (2.6)
where:
SNR = Signal to noise ratio
I = Identity matrix of order
= Hermitian transpose of the H matrix (Channel Coefficient matrix)
M = number of antenna
Figure 2.3: MIMO Capacity.
13
2.3.5 Mutual Coupling and Isolation
In MIMO applications, the signals transmitted by multiple antenna elements are
generally considered to be independent or uncorrelated. However, in reality the
current induced on one antenna produces a voltage at the terminals of nearby
elements that is characterised as mutual coupling [19]. The port to port isolation
defined as the transmission power between two of the input ports of the multiport
antenna under test. It is characterised by |S21| parameter. MIMO system requires the
|S21| to be minimised as low as possible, as isolation is directly related to the antenna
efficiency.
Isolation = -10 log10 |S21|² (2.7)
2.4 Techniques to Enhance Isolation and Its Applications
Significant research efforts have been reported lately to reduce mutual coupling.
Amongst the techniques employed are neutralization line, stub on the ground plane
and defected ground plane have been proposed. In this section, a review of previous
works conducted on the aforementioned techniques will be discussed.
2.4.1 Neutralization Line (NL)
The use of neutralization line inserted between antenna elements is based on the
concept of neutralizing two antennas operating in the same frequency band to
enhance isolation. Chebihi et al. [20], drew some current from the first antenna and
re-injected it in the second antenna with a suitable phase and magnitude to mitigate
existing coupling between elements.
Huang et al. [21] suggest that the neutralization line improves the isolation
between antenna elements. This line can be seen as an inductance to neutralize the
capacitance of these two antennas. Improvements better than 15 dB was achieved.
The structure of the proposed MIMO antenna design is shown in Figure 2.4. The
simulation results of isolation with and without the neutralizing line are illustrated in
Figure 2.5. It is evident from the results that the coupling effect between antenna
element is decreased and lowers the envelope correlation coefficient (ECC) smaller
than 0.01 through the introduction of the line. The impedance bandwidth for the
measurement analysis includes 2.45 (2.4 -2.485 GHz), 5.2 (5.15 – 5.35 GHz) and 5.8
14
(5.725 - 5.825 GHz) covering Bluetooth, WLAN and WiMAX system. The measured
isolation is better than 17 dB at 2.45 GHz and 20 dB at 5.2 and 5.8 GHz,
respectively. The total dimension of this antenna design is about 80 x 40 x 1.6 mm3.
Figure 2.4: The structure of the proposed MIMO antenna (unit: mm) [21].
Figure 2.5: The simulated isolation with and without neutralizing line [21].
It was established in [22] that the antenna port isolation is effectively
enhanced by the inclusion of the neutralization line. The proposed antenna is used for
USB dongle application. This antenna occupies an area of 30 mm x 65 mm. The
configuration of detailed dimensions of the proposed antenna is illustrated in Figure
2.6. The port isolation obtained improved from 9 dB to less than about -19 dB after
the neutralization line was connected between the elements. The MIMO
characteristics such as the TARC and ECC also showed favourable results whereby
the average TARC is below -10 dB and the values of ECC remain under 0.006 at 2.4
15
GHz frequency band. The comparison of S-parameters between the proposed antenna
and the reference antenna (without neutralization line) is depicted in Figure 2.7.
Figure 2.6: Detailed dimensions of the proposed antenna [22].
Figure 2.7: Simulated reflection coefficient and isolation of the proposed antenna.
(a) With neutralization line; (b) Without neutralization line [22].
Wang et al. introduced the use of three neutralization lines inserted between
antenna elements [23]. The proposed antenna works over the frequency of 1.62 –
2.92 GHz with a mutual coupling less than -15 dB. The radiation pattern of the
proposed antenna can cover complimentary spatial region, and the antenna design
meets the requirement of low mutual and correlation. Figure 2.8 shows the geometry
(a) (b)
16
of the proposed antenna design. The antenna was fabricated on an FR-4 substrate
with a dimension of 115 x 60 mm2.
Figure 2.8: Geometry of the proposed dual-antenna with dimensions in millimeters
(the front side is in black, and the rear side is in grey); (a) Perspective view. (b) Front
view. (c) Bottom view (metal on the front is omitted) [23].
Figure 2.9: Simulated S-parameters with and without three neutralization lines.
(a) S11; (b) S21 [23].
The simulated S-parameters with and without the three neutralization line are
depicted in Figure 2.9. It can be observed that by employing the three neutralization
lines the mutual coupling is lower than -15 dB at the desired frequency band. The
ECC achieved less than 0.05 at the entire frequency band. Neutralization line was
also used to suppress the mutual coupling for 4G mobile terminals as reported in
17
[24]. The optimized neutralization line is placed in the middle of the line to fine tune
the isolation levels. An improvement of 4 dB that are from -6 dB to less than -11 dB
was achieved at the desired frequency bands. The comparison result between
simulated and measured results shows that an ECC below 0.5 between 760 MHz and
950 MHz was achieved. The isolation level with and without neutralization line is
shown, and the comparison between simulated and measured ECC are illustrated in
Figure 2.10 and Figure 2.11, respectively.
Figure 2.10: Isolation level with and without neutralization line [24].
Figure 2.11: Simulated and measured envelope correlation coefficient (ECC) [24].
Ban et al. [25], designed their antenna with a dimension of 120 x 60 mm2 that
consists of an array of elements placed symmetrically with a U-shaped neutralization
line embedded between the antenna elements. It was found that the addition of the
neutralization line reduces the mutual coupling from -6 dB to below -10 dB for the
lower band. Low correlation of less than 0.4 is achieved for the overall desired band
that meets the requirement of a MIMO antenna. The proposed antenna is used for
GSM 850/900/1800/1900/UMTS/LTE2300/2500 operations. Figure 2.12 presents the
18
geometry of the proposed antenna. The crescent-shaped radiator as shown in Figure
2.13 was proposed in [26]. It achieved an impedance bandwidth of 54.5% over 2.4-
4.2 GHz with a reflection coefficient of less than -10 dB. The two antenna elements
are separated by 0.19λ at 2.4 GHz. The neutralization line technique inserted
between the radiators resulted with a better isolation of -17 dB. It was found to be
effective enhancing the mutual coupling, correlation coefficient from 2.4 to 4.2 GHz
frequency bands significantly. Owing to the lower mutual coupling achieved, lower
capacity loss and correlation was also achieved. The capacity loss obtained did not
exceed 0.4 bps/Hz.
Figure 2.12: Geometry of the proposed antenna [25].
Figure 2.13: Geometry of the proposed antenna [26].
19
The use of neutralization line adopted together with the grounded branch
achieved a dual wideband antenna as reported in [27]. The proposed antenna design,
only reduces the mutual coupling at the lower frequency band whilst it has minor
effect on low mutual coupling at a higher frequency. The measured mutual coupling
of the antenna that is used in mobile terminal applications is less than -15 dB with an
ECC less than 0.04. The comparison of S-parameters between the reference and the
proposed antenna is illustrated in Figure 2.14 below.
Figure 2.14: Simulated S11 and S21 for the proposed antenna (the proposed dual
antenna) the case with the F-like monopole (dual-ant 1), the dual-ant without NL
(dual-ant 2) and the dual-antenna without match branch (dual-ant 3) [27].
2.4.2 Stub on the Ground Plane
Inserting stubs is one of the techniques that has been established in reducing mutual
coupling as well as to get better isolation. One or more stubs are inserted to enhance
the isolation and it deals with the ground plane instead of the radiating elements.
Zhao et al. [28] introduced one stub on the ground plane to adjust the
impedance bandwidth and to improve the isolation between the two feeding ports.
The configuration of the proposed antenna design is shown in Figure 2.15. In this
proposed design, the stub can be viewed as a reflector to reduce the mutual coupling.
After inserting stub on ground plane, high isolation which is less than -15 dB is
achieved. The proposed antenna is a suitable candidate for some portable
MIMO/diversity UWB applications.
20
Figure 2.15: Geometry of the proposed antenna [28].
Two long protruding ground stubs namely stub 1 and stub 2 are added on the
ground plane in [29]. The proposed antenna is designed for a portable UWB
application. The proposed antenna consists of two planar monopole antennas placed
perpendicularly to each other to achieve sound isolation. Stub 1 is located in parallel
with planar monopole (PM1) and is bent to minimise the space of antenna area
whilst, a simple straight stub, stub 2 is placed in parallel with PM2. The geometry of
the proposed antenna and the simulated S-parameters with and without long ground
stub are depicted in Figure 2.16 and Figure 2.17, respectively. The result shows that
an impedance bandwidth of 3.1 – 10.6 GHz, low mutual coupling (S21) less than -15
dB, low envelope correlation coefficient less than 0.2 over the frequency band were
achieved.
Figure 2.16: Geometry of the proposed antenna [29].
21
Figure 2.17: Simulated S-parameters for single element antenna with and without
long ground stub [29].
The use of metal T-shaped stub in [30] significantly reduces the mutual
coupling at the lower frequency band. The mutual coupling exists due to the near
field between the two monopoles. The two antennas radiation patterns are separated,
and the mutual coupling is reduced upon the introduction of the vertical stub that
behaves akin to a reflector. The geometry of the proposed antenna and the
comparison of S-parameter between the reference and the proposed antenna are
illustrated in Figure 2.18 and Figure 2.19, respectively. The result shows that the
isolation S21 less than -20 dB at the lower band and S21 less than -25 dB at the upper
band are achieved. The proposed antenna ECC yields less than 0.1 which in effect,
satisfies the MIMO requirement.
22
Figure 2.18: Geometry of the proposed antenna [30].
Figure 2.19: Simulated S-parameters of proposed antenna with and without
decoupling structure.(a) S11; (b) S21 [30].
Cheng et al. [31] proposed an antenna consist of two elliptical shape
monopoles. The two stubs and slot are placed between the radiators on the ground
plane. The mutual coupling and isolation higher than 20 dB were obtained. The
authors further demonstrate the effectiveness of the stub, in order to reduce mutual
coupling [32]. The isolation was improved upon the insertion of the stub i.e. S21 < -
20 dB. The proposed antenna design reported in [33] suggested two symmetrical p-
shaped radiators as the radiating element. The configuration of the proposed antenna
design is shown in Figure 2.20. By combining a notch slot at the upper centre of the
ground plane and inserting stub in the ground, good impedance matching and
improved isolation may be achieved. An impedance bandwidth of 2.9 – 11 GHz for
S11 < -10 dB and S21 < -20 dB were achieved. Figure 2.21 illustrates the simulated
and measured results of the S-parameters.
23
Figure 2.20: The geometry of the proposed antenna [33].
Figure 2.21: Simulated and measured S-Parameters. (a) S11 and (b) S21 [33].
Hong et al. also demonstrates the effectiveness of the stub to reduce mutual
coupling in [34].Three stubs were introduced in this design and is positioned between
the two Y-shaped radiators. The geometry of the proposed antenna is shown in
Figure 2.22. Stub 1, stub 2 and the radiators are placed symmetrically with respect to
the stub 3. The isolation improved with a reading of less than -20 dB upon the
insertion of the stub. In [35] the stub is connected to the ground plane via shorting
pin. The isolation obtained after inserting stub are lower than -25 dB and – 20 dB at
the 2.45 and 5.8 GHz bandwidth, respectively. The configuration of the array and the
S-parameter characteristics of the proposed antenna are shown in Figure 2.23 and
Figure 2.24, respectively.
(a) (b)
24
Figure 2.22: Geometry of the proposed diversity antenna [34].
Figure 2.23: Geometry of the proposed MIMO antenna array [35].
Figure 2.24: S-parameter characteristic of the proposed antenna [35].
99
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