ABSTRACT
Antennas play a dominant role part in the transmission and reception of signals in wireless communication, and their development make a significant impact on the speed of a wireless link. Microstrip antennas are the most common antennas widely implemented in different communication systems due to its small size, low profile, and conformity to planar and non-planar surfaces. However, the inherent characteristics of a conventional microstrip antenna, like low gain, narrow bandwidth and wider beamwidth, limits their wide applications and makes it necessary for designs to have array configuration. In this research work, the design and simulation of microstrip patch array antenna for improving signal reception in wireless communication systems is presented. The application is for X-band frequency range of 8-12GHz. All designs and simulations were carried out using HFSS (v.15) software. The design procedure started with the design of a single element Rectangular Microstrip Patch Antenna (RMPA), and then the linear RMPA array designs of 1x2 array (2-elements), 2x2 array (4-elements) and 4x2 array (8-elements) configurations. The proposed RMPA design used an operating frequency of 10GHz, a Rogers RO4350 substrate material with dielectric constant of 3.66, and a substrate height of 31mil, to achieve a compact RMPA with a patch size small enough to fit onboard an aerial system. The patch dimensions were calculated using the transmission line model and excited using inset-fed microstrip line feeding method. The feeder networks for the array designs used a corporate feeding network, with an optimized inter-element spacing of 0.52λ. Antenna parameters such as return losses, VSWR, gain etc. of the designed antennas were obtained from HFSS software. The performance parametric results of the designed antennas were compared in terms of the stimulated antenna parameters. Based on the simulation results, all the designed antennas resonated at the desired resonant frequency of 10GHz which indicates good antenna designs. The simulation results of the single element RMPA achieved a good return loss of -19.61dB at 10GHz, with a narrow bandwidth of 2.26%, VSWR of 1.82, low gain and directivity of 6.58dBi and 6.83dBi respectively, wide beamwidth of 115.2o and an efficiency of 94.2%, while the final 4x2 array RMPA achieved an improved return loss of -28.96dB, wider bandwidth of 5.82%, VSWR of 1.14, significant high gain and directivity of 11.45dBi and 11.83dBi respectively, narrow beamwidth of 47.4o and high radiation efficiency of 91.6%. Thus, the proposed 4x2 array RMPA significantly increased the narrow bandwidth of the single element antenna by 157.1% (355.4 MHz), and greatly improved the gain of the single element RMPA by 74.0%. These results show that the proposed 4x2 array RMPA has an improved performance over the single element RMPA, and meets the main objective of improving signal reception for the X-band application in a wireless communication system. The designed antennas can be embedded in wireless devices for commercial WLAN and WiMAX applications and also for onboarding in radar and satellite wireless communication systems for various surveillance and communication purposes.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgments v
Table of Contents vi
List of Tables x
List of Figures xi
List of Plates xiii
List of Abbreviations xiv
List of Symbols xvi
Abstract xviii
CHAPTER 1: INTRODUCTION
1.1 Background of the Study 1
1.2 Problem Statements 3
1.3 Aim and Research Objectives 5
1.4 Significance of the Research. 6
1.5 Scope of Work 6
1.6 Organization of the Research 7
CHAPTER 2: LITERATURE REVIEW
2.1 Introduction to Wireless Communication Systems 8
2.2 Overview of Antenna System 9
2.3 Types of Antennas 11
2.3.1 Classification based on Radiation Pattern 12
2.3.2 Classification based on Structure 13
2.4 Basic Parameters of Antenna 18
2.5 Introduction to Microstrip Patch Antennas 26
2.5.1 Types of Patch Antennas 27
2.5.2 Advantages of Microstrip Antennas 27
2.5.3 Disadvantages of Microstrip Antennas 28
2.6 Categories of Waves in Microstrip Structure 29
2.7 Excitation Techniques of Microstrip Antenna 30
2.7.1 Microstrip Line Feed 31
2.7.2 Coaxial Feed 32
2.7.3 Aperture Coupling Feed 32
2.7.4 Proximity Coupling Feed 33
2.7.5 Coplanar Waveguide (CPW) Feed 34
2.8 Method of Analysis 35
2.8.1 Transmission Line Model 36
2.8.2 Cavity Model 43
2.8.3 Full Wave Model 44
2.9 Antenna Arrays 45
2.9.1 Antenna Array Factor (AF) 46
2.10 Antenna Array Feed Network 47
2.11 Power Divider 48
2.12 Impedance Matching of Array Feeders 49
2.13 Mutual Coupling in Antenna Array 51
2.14 Relative Displacement of Radiating Elements 52
2.15 Review of Related Literatures 52
2.16 Summary of Literature Review 56
2.17 Identified Knowledge Gaps 57
CHAPTER 3: DESIGN METHODOLOGY
3.1 Methodology Overview 58
3.2 Choice of Simulation Software 58
3.3 Flowchart of Design Methodology 59
3.4 Design Procedure 60
3.5 Design Specification 60
3.6 Design of Single Element Microstrip Patch Antenna 62
3.6.1 Calculation of Design Parameters 62
3.6.2 Geometry of Proposed Inset-fed RMPA Design 65
3.7 Design of Rectangular Microstrip Antenna Arrays 66
3.7.1 Design of a 1x2 Rectangular Microstrip Antenna Array 68
3.7.2 Design of a 2x2 Rectangular Microstrip Antenna Array 70
3.7.3 Design of a 4x2 Rectangular Microstrip Antenna Array 71
3.8 Design Optimization of Microstrip Patch Antenna Model 73
CHAPTER 4: RESULTS AND DISCUSSIONS
4.1 Results 74
4.1.1 Results of the Single Element Rectangular Microstrip Antenna 74
4.1.2 Results of the Design of a 1x2 Rectangular Microstrip Antenna Array 77
4.1.3 Results of the Design of a 2x2 Rectangular Microstrip Antenna Array 79
4.1.4 Results of the Design of a 4x2 Rectangular Microstrip Antenna Array 80
4.2 Summary of Simulation Results of Different Designed RMPA
Configurations 82
4.3 Comparison of Performance Improvements of Different RMPA Arrays 83
4.3.1 Return Loss 83
4.3.2 Bandwidth 84
4.3.3 Voltage Standing Wave Ratio (VSWR) 85
4.3.4 Gain 86
4.3.5 Directivity 87
4.3.6 Radiation Pattern and Beamwidth 88
4.3.7 Power Radiated (Tx) and Power Received (Rx) 89
4.3.8 Antenna Radiation Efficiency 90
CHAPTER 5: CONCLUSION AND RECOMENDATIONS
5.1 Conclusion 91
5.2 Future Work and Recommendations 92
References 94
Appendices 103
LIST OF TABLES
2.1 Summary of Feeding Techniques in Microstrip Patch Antenna Design 35
3.1 Microstrip Antenna Design Specifications 62
3.2 Dimensions for Single Element Inset Fed RMPA 66
3.3 Geometric Parameters of RMPA Array Matching Impedance Feed Network 68
3.4 Dimensions for the 1x2 Array Inset Fed RMPA 69
3.5 Dimensions for the 2x2 Array Inset Fed RMPA 70
3.6 Dimensions for the 4x2 Array Inset Fed RMPA 72
4.1 Summary of Simulation Results of Different Designed RMPA
Configurations 83
4.2 Comparison of Power Radiated and Received of Designed RMPA Array 89
LIST OF FIGURES
1.1 Block Diagram of a Simple Microstrip Antenna Array 2
2.1 Communication System. 9
2.2 Classification of Antenna. 12
2.3 Classification of Antenna Based on Structure 14
2.4 Bandwidth Estimation from Return Loss Plot of an Antenna Design 23
2.5 Radiation Pattern of a Generic Directional Antenna 23
2.6 Antenna Beamwidth 24
2.7 Types of Antenna Polarization 25
2.8 Schematic diagram of a typical Microstrip Patch Antenna. 26
2.9 Common Shapes of Patch Antennas 27
2.10 Different Types of Microstrip Line Feed 31
2.11 Typical Transmission Line and Electric Field Lines of MPA 36
2.12 Transmission Line Model and Circuit Equivalent of MPA 38
2.13 Inset Microstrip Line Feed. 41
2.14 Different Types of Feed Networks for Antenna Array 48
2.15 Types of Microstrip Bend 49
2.16 Quarter Wave Transformer Impedance Matching 50
2.17 Mutual Coupling of E-plane and H-plane Layout of Array Elements 51
3.1 Flow Chart of Proposed Antenna Design 59
3.2 Top-view Dimensions of Single Element Inset-fed RMPA Design 65
3.3 Designed Single Element Inset-fed RMPA using HFSS Software. 66
3.4 Designed 1x2 Array Inset-fed RMPA using HFSS Software 69
3.5 Designed 2x2 Array Inset-fed RMPA using HFSS Software 71
3.6 Designed 4x2 Array Inset-fed RMPA using HFSS Software 73
4.1 Return Loss (S11) versus Frequency Plot of Single Element RMPA 74
4.2 VSWR versus Frequency Plot of Single Element RMPA 75
4.3 Radiation Pattern of Single Element RMPA in Polar Plot 76
4.4 Single Element 3D Gain Plot 76
4.5 Single Element 3D Directivity Plot 76
4.6 Return Loss (S11) versus Frequency Plot of 1x2 Array RMPA 77
4.7 VSWR versus Frequency Plot of 1x2 Array RMPA 78
4.8 Radiation Pattern of 1x2 Array RMPA in Polar Plot 78
4.9 3D Gain Plot of 1x2 Array RMPA 78
4.10 3D Directivity of 1x2 Array RMPA 78
4.11 Return Loss (S11) versus Frequency Plot of 2x2 Array RMPA 79
4.12 VSWR versus Frequency Plot of 2x2 Array RMPA 79
4.13 Radiation Pattern of 2x2 Array RMPA in Polar Plot 80
4.14 3D Gain Plot of 2x2 Array RMPA 80
4.15 3D Directivity of 2x2 Array RMPA 80
4.16 Return Loss (S11) versus Frequency Plot of 4x2 Array RMPA 81
4.17 VSWR versus Frequency Plot of 4x2 Array RMPA 81
4.18 Radiation Pattern of 4x2 Array RMPA in Polar Plot 82
4.19 3D Gain Plot of 4x2 Array RMPA 82
4.20 3D Directivity of 4x2 Array RMPA 82
4.21 Comparison of Simulated Return Loss of Single Element and Antenna Arrays 84
4.22 Comparison of Simulated Bandwidth of the Single Element and Antenna Arrays 85
4.23 Comparison of Simulated VSWR of Single Element and Antenna Arrays 86
4.24 Comparison of Simulated Gain of the Single Element and Antenna Arrays 87
4.25 Comparison of Simulated Directivity of the Single Element and Antenna Arrays 88
4.26 Comparison of Simulated RMPA Radiation Efficiencies (%) 90
LIST OF PLATES
2.1 Wire Antenna Configurations 14
2.2 Aperture Antenna Configurations 15
2.3 Typical Array Antennas 16
2.4 Typical Configurations of Log-periodic Antennas 16
2.5 Typical Parabolic Reflector Antenna 17
2.6 Categories of waves in Microstrip Structure 30
2.7 Microstrip Feed and Equivalent Circuit Diagram 31
2.8 Coaxial Feed and Equivalent Circuit Diagram 32
2.9 Aperture Coupled Feed and Equivalent Circuit Diagram 33
2.10 Proximity Feed and Equivalent Circuit Diagram 34
2.11 Coplanar Waveguide (CPW) Feed 34
2.12 Physical Length and Electric Field Line of a Typical RMPA 37
2.13 Cavity Model Magnetic Wall and Charge Distribution in Patch Antenna 43
2.14 Antenna Array Configurations 46
2.15 A Typical Quarter Wave Transformer 50
LIST OF ACRONYMS/ABBREVIATIONS
ADS Advanced Design System
COMSOL COMputer and SOLution
CST MS Computer Simulation Technology Microwave Studio
DGS Defected Ground Structure
EBG Electromagnetic Band Gap
E-field Electric Field
FEM Finite Element Model
FDTD Finite Difference Time Domain
GPS Global Positioning Systems
GSM Global System for Mobile communication
H-field Magnetic Field
HPBW Half Power Beam Width
HP MDS HP Microwave Design System
HFSS High Frequency Structure Simulator
IE3D Integral Equation 3-Dimensional
MATLAB MATrix LABoratory
MMICs Microwave Monolithic Integrate Circuits
MoM Method of Moment
MPA Microstrip Patch Antenna
MWO Microwave Office
PCB Printed Circuit Board
PIFA Planar Inverted – F Antenna
QWT Quarter Wavelength Transformer
RMPA Rectangular Microstrip Patch Antenna
SAR Synthetic Aperture Radar
UAV Unmanned Aerial Vehicles
UHF Ultra High frequency
VHF Very High Frequency
VSWR Voltage Standing Wave Ratio
WLAN Wide Local Area Network
WiMAX Worldwide Interoperability for Microwave Access
LIST OF SYMBOLS
c Free-space velocity of light
λo Free-space wavelength
ε_r Dielectric constant of substrate
ε_eff Effective dielectric constant
h Height (Thickness) of dielectric substrate
δ Effective loss tangent
W Width of patch
L Length of patch
L_eff Effective length of the patch
Patch length extension
Zo Characterization input impedance.
Lf Length of the transmission feed line
Wf Width of the transmission feed line
y_o Insert feed depth
g Gap of the feed line
Lg Length of ground plane
Wg Width of ground plane.
Γ Reflection coefficient
f_o Operating frequency
f_L Lower bound frequency
f_C Centerfrequency
f_H Higher bound frequency
Pr Power radiated from the patch
G Gain
D Directivity
η Radiation efficiency
k Wave vector
β Phase difference
dB Decibel
MHz Mega Hertz
GHz Giga Hertz
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Wireless communication services have been growing at a very rapid rate in recent years (Parchin et al., 2019), and the need for compact and multifunctional wireless communication systems has spurred the development of antennas with small size (Ullah et al., 2018). According to the IEEE Standard Definitions, antenna or aerial is defined as electromagnetic device used for radiating or receiving electromagnetic wave signals in free space (Balanis, 2016). In other words, antennas act as an interface for electromagnetic energy, propagating between the transmission line and free space (Kumar et al., 2018). Thus, in today’s wireless technologies, antennas play critical role and are the most important component in all wireless communication system (Kumbar, 2015; Yildiran, 2017).
With the increasing number of wireless users and limited available bandwidth, wireless service providers are always striving to improve network capacity and coverage, as to satisfy the mobility need of users (Liu et al., 2012; Yildiran, 2017). This has caused increased evolution in antenna engineering that tries to satisfy the user’s need for low-cost, miniaturized, and compactable antennas (Wahab et al., 2019). Amongst the various types of antennas such as wire antennas and reflector antennas, microstrip antennas are most popular, versatile, and easy to fabricate (Elias,2014). The microstrip antenna is very popular due to its distinguishing characteristics such as low profile, low cost, light weight, ease of fabrication, and conformity to planar and non-planar surfaces (Tarpara et al., 2018). These advantages have increased the usage of microstrip antennas in various applications in Broadcast systems, Global Positioning System (GPS), Mobile and Satellite communication systems, Multiple-Input Multiple-Output (MIMO) systems, Radio-Frequency Identification (RFID), Vehicle Collision Avoidance System, Remote Sensing and Radar systems, Surveillance systems, Missile Guidance etc. (Garg et al., 2001; Liu et al., 2012). Nevertheless, despite these advantages of microstrip antennas, they are associated with some disadvantages such as low gain, narrow bandwidth, and surface waves excitations (Ullah et al., 2018).
To overcome these disadvantages with using microstrip antennas, many researches carried out in antenna design have proposed techniques for improving the low gain and narrow bandwidth of microstrip antenna (Kaur and Rajni, 2013; Khraisat, 2012; Kim, 2010). Among the proposed techniques, the most popular for improving microstrip antenna performance in terms of increased gain and bandwidth include: using thick substrate, use of resonant slots called defected ground structures (DGSs) in the ground plane, use of a low dielectric substrate, using multi-resonator stacked patch structure, use of various impedance matching and feeding techniques, and the use of array antenna configuration (Liu, et al., 2012; Kim, 2010; Islam et al., 2009). The use of Electromagnetic Band Gap (EBG) is another technique also employed to reduce surface waves excitation in the substrate (Akhtar et al., 2012). However, the most commonly used techniques for improving microstrip antenna gain and bandwidth is by using array antenna configuration (Balanis, 2016; Khraisat, 2012; Roy et al., 2013). A simple microstrip antenna element in array configuration is shown in Figure 1.1.
Figure 1.1: Block Diagram of a Simple Microstrip Antenna Array
Though microstrip antennas are important as single radiating element, its major advantages are realized in applications that require single elements to be arrange in array (Park et al., 2003, Balanis, 2016) as shown in Figure 1.1. Microstrip antenna arrays have received considerable attention due to their importance in radar and satellite communication systems (Idigo et al., 2011). The major advantages of using antenna arrays in communication systems are to achieve high gain and directivity, improve efficiency, steer beam, cancel out interference and increase Signal-to-Noise Ratio (SNR) of an antenna (Vijaykumar, 2017).
This research work attempts to design and simulate a microstrip patch array antenna for improving signal reception in a wireless communication system. Nowadays, a lot of software have been developed for design and simulation of microstrip patch antennas (Odeyemi et al., 2011), out of which HFSS software has been used for the work mentioned in this thesis.
1.2 PROBLEM STATEMENT
As wireless communication in today’s genre plays vital role in almost all the areas of life, achieving seamless wireless communication is a big issue. Wireless communication service providers and users nowadays demand a wireless unit with antennas that are compactable, small, and conformable with overall wireless system. These antennas must in their functionalities, radiate low power with good signal reception (Pozar and Schaubert, 1995).
The poor signal reception in wireless communication is caused among other things by significant performance degradation due to random losses that come from low bandwidth, longer delays, high Bit-Error Rate (BER), and frequent disconnections (Oluwole and Srivastava, 2017; Abba et al., 2015). Though, wireless communication systems offer many advantages to mobile users, the mobility it offers, is in itself a generator for packet loss, increased packet delay, interference, congestion, low Signal-to-Noise Ratio (SNR) and decreased throughput (Nyitamen and Ugalahi, 2018). Nguyen (2008) observed that wireless networks are traditionally short on bandwidth. Thus, the design consideration for an antenna structure of a wireless communication system needs to meet the end-user’s demands with sufficient bandwidth and high gain (Liu et al., 2012).
The conventional microstrip patch antenna, though advantageous in many areas, suffers from narrow bandwidth (<5%) and low gain, owing predominantly to the promulgation of surface waves (Singh, 2017; Islam et al., 2009; Parizi, 2017). Surface wave promulgation is a severe problem in microstrip antenna design, as it diminishes antenna efficiency and gain, limits bandwidth, surges end-fire radiations, escalates cross-polarization and limits the useful frequency range of microstrip antennas (Hala, 2010). Although, increasing the thickness of the dielectric substrate in the design of microstrip patch antenna, can increase antenna bandwidth, this process causes surface waves to use more of the delivered power, leading to increased antenna power loss (Parizi, 2017). Furthermore, as the size of microstrip increases, it can allow resonant frequencies of two or more resonant modes to exist, leading to antenna performance instabilities.
More so, the demand for long-distance communication in many applications, has made it necessary that antenna designs should have a very high gain. The radiation pattern of a conventional single microstrip antenna element is relatively wide, with low gain and directivity, and is not suitable for point-to-point communication where antenna is required to have high directivity (Alsager, 2011; Khan et al., 2016). These drawbacks make the utilization of single element Microstrip Patch Antenna (MPA) not recommendable for application where long distance or high directivity is needed.
However, in view of these disadvantages and problems that affect the performance of a conventional microstrip patch antenna, numerous techniques are employed in designing MPA to enhance its antenna performance (Chavan et al., 2019; Khraisat, 2018; Kaur, 2016). One of these techniques involves the use of microstrip antenna array configurations (Khraisat, 2012; Wahab et al., 2019). This technique of improving the bandwidth and gain of microstrip antenna using antenna array configuration is proposed in many literatures. The antenna array is required to have wider bandwidth, high gain, narrow beam, low sidelobes, and as well as small physical size as reasonably possible (Najeeb et al., 2016). In this research work, microstrip patch array antenna is designed and simulated for improving signal reception in wireless communication systems.
1.3 AIM AND RESEARCH OBJECTIVES
The aim of this thesis is to design and simulate microstrip patch array antenna that can improve signal reception in wireless communication system. The research pursued a lightweight antenna that operates at an operating frequency of 10GHz in the X-band range of 8-12GHz, with a wide bandwidth, and a low signal loss. The specific objectives of the study are:
i. To review related literatures and ascertain current state of art in the field of study.
ii. To characterize a typical Microstrip Patch Antenna (MPA) by determining the parameters that improve signal reception for an antenna used in a wireless communication system.
iii. To design and simulate a single element inset-fed Rectangular Microstrip Patch Antenna (RMPA) from the characterized parameters with operating frequency of 10GHz using finite element model based HFSS software.
iv. To investigate and simulate the design of 1x2-array, 2x2-array and 4x2-array RMPA configurations that improves performance parameters of the single element RMPA.
v. To study obtained simulation results, and compare the degree of antenna performance improvements in both designed single element and RMPA array configurations.
1.4 SIGNIFICANCE OF THE RESEARCH
This research work is most significant in meeting the demand for long distance wireless communication, and for various X-band applications in Synthetic Aperture Radar (SAR) onboard aerial platforms. The significance of microstrip antenna array design application, as a panacea for achieving effective signal reception in wireless communication system, will avail the communication industry with a market full of lightweight antenna system that offers high gain and directivity, improved efficiency, wider beamwidth, agile beam steering, decreased signal interference and increase Signal-to-Noise Ratio (SNR) for applications used in mobile handheld communication devices, Global Positioning System (GPS), Direct Broadcast Satellite system, remote sensing, unmanned aerial vehicles, radar system and satellite communication systems.
1.5 SCOPE OF THE STUDY
The scope of this research work focuses on the design and simulation of inset-fed Rectangular Microstrip Patch Antenna (RMPA) array for improving signal reception in a wireless communication system. The work is restricted mainly to the operating frequency of 10GHz in the X-band frequency range of 8-12GHz. ANSYS HFSS (v.15) software will be used for all the designs and simulations to be performed in this work. This study will center on using Rogers RO4035 (tw) substrate material with dielectric constant 〖(ε〗_r) of 3.66, and a height (h) of 31 mil, to firstly, design a single element inset-feed Rectangular Microstrip Patch Antenna (RMPA) that will be used to design the proposed 1x2 array, 2x2 array, and 4x2 array RMPA configurations. After simulations, the obtained simulation results of the designed single element RMPA and array RMPA configurations will be compared for antenna performance improvement of signal reception in wireless communication system.
1.6 ORGANIZATION OF THE THESIS
This thesis is divided into five (5) chapters. Chapter one provides an introduction into the background of the study, problem statement, aims/objectives, significance, and scope of the research. Chapter two reviewed existing literature on MPA array design, starting with an introduction to wireless communication systems, to antenna overview and types, basic parameters of antenna, introduction to microstrip patch antenna, categories of waves in microstrip structure, feeding techniques and method of analysis of MPA. The chapter is concluded with review, summary and research gap of related literatures pertaining to MPA design and simulation. Chapter three presents an overview of the design methodology, choice of HFSS simulating software, design flowchart, design considerations, calculation of design parameters for single element Rectangular Microstrip Patch Antenna (RMPA), design of the RMPA arrays (1x2, 2x2, 4x2 array) and simulation procedures of the project. Chapter four presents the analysis of the simulated HFSS results of the radiation characteristics from all designs of single element and array antenna design. Comparisons of the degree of antenna signal performance improvement with respect to the antenna parametric results are also presented and tabulated in this chapter. Finally, Chapter five presents the conclusions drawn from this research work, and suggests future scope of work.
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