v
MINIATURIZED WIDEBAND HYBRID DIRECTIONAL COUPLER USING
SLOW WAVE STRUCTURE SND MEANDERING LINES TECHNIQUE
CHONG JAW CHUNG
A thesis submitted in fulfilment of the
requirements for the award of the degree of
Master of Engineering (Electrical)
Faculty of Electrical Engineering
Universiti Teknologi Malaysia
AUGUST 2016
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Specially dedicated to
my friends, and family.
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ACKNOWLEDGEMENT
In the process of completing this research project, i would like to express my
warmest appreciation to my supervisor, Dr. You Kok Yeow, a professional member
of IEEE, for his professional advice and consultation in dealing with such
challenging research.
Also, I would like to thank Mr. Hou Kit, Yi Lung and Jia Yong who are PhD
students under supervising of Dr.You. they the person who give me special guidance
in numerical programming and circuit simulation using EM software. They provides
a lot of constructive personal tutoring in the technical aspect, especially in the
process of PCB fabrication and Data measurement.
Furthermore, I would like to thank Prof Dr. Ruzairi, who is the Head of
Department in RMC (Research Management Centre), for his kindness of approving
the great amount of research grant allocated by MOHE (Ministry of Higher
Education), Malaysia. The research grant is essential in purchasing of material or
apparatus for dealing with such challenging research.
Next, the librarians at Sultanah Zanariah Library (PSZ) also play a significant
role in helping me in completing this research project. They do provided some useful
advice in what kind of books should I borrow for references especially in engineering
field. The PSZ is also an informative place in looking for high impact factor journals,
which is essential in making reference for latest ideas in electrical engineering field.
Finally, I would like to express my greatest appreciation to all my friends and
colleagues who give me a lot of help in completing my thesis. Then, I would like to
say thank you to my family for their support and patient throughout the whole
research period which took about three years.
Thank you very much. I really appreciate it.
.
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ABSTRACT
Branch-line coupler is an important element in modern microwave circuit. Amore compact and wideband prototype is preferred, since; it lowers the productioncost and could operate well in wider bandwidth. However, most conventional branchline couplers consume bigger spacing and operate in narrow bandwidth. In thisresearch, a wideband three-branch line coupler and four-branch line coupler, whichare 20.6 % and 50.2 % respectively, compact than conventional couplers, had beenminiaturized using Slow Wave Structure (SWS) and Meandering Line (ML)techniques. The cascade method is implemented on conventional coupler forincreasing its bandwidth. The fabricated area of modified three-branch line and four-branch line coupler is (1729.9 mm2) and (1927.8 mm2), respectively. Both prototypeswere fabricated using etching technique. The performance results were obtainedusing Keysight E5071C VNA (Vector Network Analyzer). Calibration had beendone to VNA for all types of measurement. Its important parameters such as returnloss |S11|, through |S21|, coupling |S31| and isolation |S41| are studied for bothconventional and modified designs, within the frequency range of 1.0 GHz to 5.0GHz. The AWR Microwave Office Software is used for simulation, and designingthe prototypes using 2.4 GHz as centre frequency, where the operating bandwidthremains at 1.5 GHz to 3.5 GHz. The performance of both prototypes were validatedby comparing the simulation and measurement results, where, they show goodagreement in S-parameters performance similar to the conventional ones, or evenbetter. The modified three-branch line coupler experienced |S11| below -13 dB withoperating frequency band of 1.5 GHz, which is 0.1 GHz wider than conventionaldesign performance with 1.4 GHz frequency band, whereas, the modified four-branch line coupler experienced |S11| below -13 dB with operating frequency band of2.0 GHz, which is 0.6 GHz wider than conventional design performance with 1.4GHz frequency band. In conclusion, the modified prototypes are more compact,making it make portable and operates well within wider operating bandwidth.
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ABSTRAK
Cawangan talian pengganding adalah elemen penting dalam litar gelombangmikro moden. Satu prototaip lebih padat dan jalur lebar telah direkacipta kerana iamerendahkan kos pengeluaran dan boleh beroperasi dengan baik dalam jalur lebaryang lebih besar. Walau bagaimanapun, kebanyakan cawangan talian penggandingkonvensional mengambil jarak yang lebih besar dan beroperasi dalam jalur lebarsempit. Dalam kajian ini, tiga cawangan garis talian pengganding dan empatcawangan garis talian pengganding, yang 20.6% dan 50.2% masing-masing, padatdaripada pengganding konvensional, telah bersaiz kecil menggunakan StrukturGelombang Perlahan (SWS) dan teknik garis berliku-liku (ML). Kaedah latadilaksanakan pada pengganding konvensional untuk meningkatkan jalur lebar.Kawasan prototypaip yang diubahsuai garis tiga cawangan dan empat cawangangaris pengganding adalah (1729,9 mm2) dan (1927,8 mm2), masing-masing. Kedua-dua prototaip direka menggunakan teknik punaran. Keputusan pengukuran telahdiperolehi dengan menggunakan Keysight E5071C VNA (Vektor PenganalisisRangkaian). Penentukuran telah dilakukan untuk VNA untuk semua jenispengukuran. Parameter yang penting seperti kehilangan pulangan |S11| melalui |S21|,gandingan |S31| dan pengasingan |S41| dikaji untuk kedua-dua reka bentukkonvensional dan diubah suai, dalam julat frekuensi 1.0 GHz kepada 5.0 GHz.Perisian AWR Microwave Office digunakan untuk simulasi, dan mereka bentukprototaip menggunakan 2.4 GHz sebagai frekuensi pusat, di mana jalur lebar operasikekal pada 1.5 GHz kepada 3.5 GHz. Prestasi kedua-dua prototaip telah disahkandengan membandingkan keputusan simulasi dan keputusan pengukuran, di mana,kedua-dua keputusan menunjukkan perjanjian yang baik dalam keputusan S-parameter yang sama dengan prototaip konvensional, atau lebih baik. Protototaipyang diubah suai dengan tiga cawangan mengalami |S11| di bawah -13 dB denganoperasi jalur frekuensi 1.5 GHz, iaitu 0.1 GHz lebih luas daripada prestasi rekabentuk konvensional dengan 1.4 GHz jalur frekuensi, manakala, prototaip yangdiubah suai empat cawangan garis pengganding mengalami |S11| di bawah -13 dBdengan operasi jalur frekuensi 2.0 GHz, iaitu 0.6 GHz lebih luas daripada prestasireka bentuk konvensional dengan 1.4 GHz jalur frekuensi. Kesimpulannya, prototaipyang diubahsuai adalah lebih padat, menjadikannya membuat mudah alih danberoperasi dengan baik dalam lebar jalur operasi lebih luas.
TABLE OF CONTENTS
CHAPTER TITLE PAGE
DECLARATION
DEDICATION ii
ACKNOWLEDGEMENTS iii
ABSTRACT iv
ABSTRAK v
TABLE OF CONTENTS vi
LIST OF TABLES x
LIST OF FIGURES xi
LIST OF ABBREVIATIONS xv
LIST OF SYMBOLS xvi
1 INTRODUCTION
1.1 Introduction 1
1.2 Background of the Problems 2
1.3 Problem Statement 4
1.4 Objectives of the Study 4
1.5 Scope of the project 5
1.6 Report Organization 6
2 LITERATURE REVIEW
2.1 Introduction 7
2.2 Directional Coupler Theory 8
2.3 Conventional Quadrature Hybrids 10
2.4 Miniature Techniques for Microstrip Transmission Line 15
2.4.1 Slow Wave Structure (SWS) Techniques 15
2.4.2 Meandering Technique for Coupler Miniaturization 17
2.4.3 Review of Miniature Branch-Line Coupler 17
2.5 Lumped-Element Circuit Representation for Coupler 45
2.6 Summary 47
3 RESEARCH METHODOLOGY 49
3.1 Introduction 49
3.2 Methodology 49
3.2.1 Prototype Design and Simulation (Stage 1) 51
3.2.2 Prototype Fabrication (Stage2) 52
3.2.3 Prototype Measurement (Stage 3) 53
3.3 Prototype Design Specifications and Dimensions 55
3.4 Branch Line Design Theory 55
3.5 Three Branch-Line Coupler Design 56
3.5.1 Conventional Coupler 56
3.5.2 Modified Three-branch Coupler 57
3.6 Four Branch-Line Coupler 58
3.6.1 Conventional Wideband Coupler 58
3.6.2 Modified Wide-Band Coupler (Type-1) 59
3.6.3 Modified Wide-Band Coupler (Type-2) 60
3.6.4 Design Dimension of Modified Branch-Line Coupler 61
3.7 Comparison of Modified and Conventional Prototype Design 64
3.8 Summary 65
4 RESULT AND DISCUSSION 66
4.1 Introduction 67
4.2 Comparison of Measurement and Simulation 68
4.2.1 Conventional Three-branch Coupler 68
4.2.2 Modified Three-Branch Line Coupler 69
4.2.3 Conventional Four-branch Line Coupler 70
4.2.4 Modified Four-branch Line Coupler type-1 72
4.2.5 Modified Four-branch Coupler Type-2 734.3 Performance Comparison of Conventional and 74
Modified Prototype4.3.1 Three-branch Coupler Comparison 74
4.4 Comparison of Phase Different and 75 ^-parameters Bandwidth4.4.1 Conventional Three-branch Coupler 75
Phase Different
4.4.2 Modified Three-branch Coupler 76
Phase Different
4.4.3 Conventional Four-branch Coupler 77
Phase Different
4.4.4 Modified Four-branch Coupler 78
Type-1 Phase Different
4.4.5 Modified Four-branch Coupler Type-2 79
Phase Different
4.5 Analysis of Bandwidth Performance 804.5.1 Conventional Three-branch Coupler 80
4.5.2 Conventional Four-branch Line Coupler 81
4.5.3 Modified Three-branch Coupler 83
4.5.4 Modified Four Branch Line Coupler Type-1 85
4.5.5 Modified Four Branch Line Coupler Type-2 86
4.5.6 Additional Layer and Bandwidth Performance 88
4.6 Summary 89
5 CONCLUSIONS AND RECOMMENDATION 90
5.1 Conclusions 90
5.2 Recommendations for Future Work 92
REFERENCES 93
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LIST OF TABLES
TABLE NO. TITLE PAGE
2.1 Miniaturised Branch line Coupler using 19slow wave structure.
2.2 Miniaturized branch line coupler using 37meandering line structures.
3.1 Dimension for modified three-branch directional 49coupler layout.
3.2 Dimension for modified three-branch directional 61coupler layout.
3.3 Dimension for modified four-branch directional 62coupler layout
3.4 Dimension for designed directional coupler 64
4.1 Performance comparison of three branch-line 83coupler.
4.2 Performance comparison of four branch-line 87couplers.
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LIST OF FIGURES
FIGURE NO. TITLE PAGE
1.1 The waveguide hybrid junction 1
1.2 Diagram of two-element Directional Coupler 2(a) Diagrammatic configuration (b) 3D configuration
1.3 Interdigitated 3-dB Coupler 2
2.1 Block diagram of a four-port network 8
2.2 A basic coupled transmission line 9
2.3 Quarter-wave branch line hybrid circuit 11
2.4 (a) Insertion loss at two output ports (Port-2 and Port-3) 11(b) Phase balance between two output ports(c) Return loss at input port (Port-1) and isolation port (Port-4)
2.5 Prototype proposed by Muraguchi 12fabricated on fine grained alumina
2.6 Multi-section branch line hybrid 13
2.7 Comparison of the regular structure length with 15slow wave structure (SWS) for the same electrical length
2.8 Slow wave structure (SWS) design (Sung et al., 2005) 16
2.9 (a) Compact branch line coupler using slow wave structure 18
(b) Conventional branch line coupler. (Sun et al., 2009)
2.10 SWS coupler and its performance 19
xi
2.11 Meandering line coupler and its performance 37
2.12 Lumped element version of branch line hybrid 45
2.13 First-order lumped element hybrid 46
2.14 Mixed element hybrid 46
3.1 Research methodology flow chart and main stages 49
3.2 The procedure of prototype design and simulation 50
3.3 The procedure of prototype fabrication 51
3.4 Keysight E5071C VNA for prototype measurement 52
3.5 The procedure of prototype measurement 53
3.6 The design parameters: Za = 37.4 Ω, Zb = 96.9 Ω, 55
Zc = 63.7 Ω, and θ = 90º
3.7 Design parameter of a modified three branch coupler 56where Za = 50Ω, θ= 90º
3.8 Wideband design parameters: Za= 54 Ω, Zb= 58.3 Ω, 57Zc= 143 Ω, θ = 90º
3.9 Design parameter of a modified three branch coupler type-1: 58Zc = 143 Ω, Za = 50Ω, θ = 90º
3.10 Design parameter of a modified three branch coupler type-2: 59Zc = 143 Ω, Za = 50Ω,θ = 90º
3.11 Design dimension for (a) Modified three-branch coupler. 60(b) Modified four-branch coupler
3.12 Conventional three branch coupler design 63
3.13 Conventional design and modified design for 63three branch coupler
3.14 Conventional four-branch coupler design 63
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3.15 Conventional design and modified design for 64four branch coupler
3.16 Modified four branch coupler and modified 64three branch coupler
4.1 S-parameter performance for conventional 68three-branch coupler
4.2 S-parameter performance for modified 69three-branch coupler
4.3 S-parameter performance for conventional 70four-branch coupler
4.4 S-parameter performance for modified 71four-branch coupler type-1
4.5 S-parameter performance for modified 72four-branch coupler type-2
4.6 Comparison for conventional and modified 73three-branch coupler
4.7 Phase different performance of conventional 74three-branch coupler
4.8 Phase different performance of modified 75three-branch coupler
4.9 Phase different performance of conventional 76four-branch coupler
4.10 Phase different performance of modified 77four-branch coupler type-1
4.11 Phase different performance of modified 78four-branch coupler type-2
4.12 Bandwidth performance of conventional 80three-branch coupler
xiii
4.13 Bandwidth performance of conventional 81four branch coupler
4.14 Bandwidth performance of modified 83three-branch coupler
4.15 Bandwidth performance of modified 85four-branch coupler type-1
4.16 Bandwidth performance of modified 86four-branch coupler type-2
4.17 Bandwidth performance comparison 88for additional substrate
xv
LIST OF ABBREVIATIONS
ATL – Artificial Transmission Line
AWR – Apply Wave Research
BCB – Benzo Cyclobutene
CCS CL – Complementary-Conducting Strip Coupling Line
ECPW – Elevated Coplanar Waveguides
LTCC – Low Temperature Co-fired Ceramics
ML – Meandering Lines
MMIC – Monolithic Microwave Integrated Circuit
MPC – Microstrip Printed Circuit
PCB – Printed Circuit Board
SWS – Slow Wave Structure
TFMS – Thin Film Microstrip Lines
TLs – Transmission Lines
UHF – Ultra High Frequency
VNA – Vector Network Analyzer
VHF – Very High Frequency
xvi
LIST OF SYMBOLS
D – Dimensions
|S11| – Return loss
|S21| – Insertion loss
|S31| – Coupling
|S41| – Isolation
|S21| – Insertion loss
S – Scattering parameters2 – Through factor
2 – Coupling factor
P1 – Input power
P2 – Through power
P3 – Coupled power
P4 – Isolated power
C – Coupling factor
dB – Decibel
– Phase different
n – Number of coupler’s main lines
ν – Phase velocity
L – Inductance per length
C – Capacitance per length
λ – Electrical wave length
Zo – Characteristic impedances
μ – Mikro
xvii
– Normalized frequency
Cs – Shunt Capacitor values
Cp – Coupling Capacitor values
εr – Dielectric constant
tan δ – Loss tangent
h – Substrate thickness
W – Strip width
θ – Phase in degree
fc – Center frequency
∆f – Operating bandwidth
xviii
CHAPTER 1
INTRODUCTION
1.1 Introduction
A hybrid junction is a four port network in which a signal on any one of the ports
divides between two out ports with the remaining port being isolated (Rizzi, 1988).
The first hybrid junction, known as Magic Tee Junction was developed by (Tyrell,
1947) as shown in Figure 1.1. The hybrid junction was modified by Mumford (1947),
and transformed it into slot directional coupler as shown in Figure 1.2. Finally, it was
improved again and turned into microstrip directional coupler by Lange (1969), as
shown in Figure 1.3.
Figure 1.1: The waveguide hybrid junction
2
(a) (b)
Figure 1.2: Diagram of two-element Directional Coupler
(a) Diagrammatic configuration (b) 3D configuration (Mumford et al., 1947)
Figure 1.3 Interdigitated 3-dB Coupler (Lange et al., 1969)
1.2 Background of the Problems
In the modern era, the slow wave structure (SWS) was applied by Sun et al.
(2005) to miniaturize conventional coupler. The performance of its S-parameters
remains almost the same value as conventional design. However, this approach does
not improve its bandwidth, where the operating bandwidth is remaining narrow.
3
Most research emphasis size miniaturization only in two branch coupler.
Sakagawi et al. (1997) proposed two branch line coupler miniaturization using eight
stubs. Eccleston et al. (2003) employing artificial transmission line (ATL) to
miniaturize the two-branch coupler. Here, miniaturization is conducted to three
branch line coupler and four-branch line coupler using slow wave structure (SWS)
and meandering lines technique (ML).
Some researcher did emphasize the miniaturization of three branch line coupler.
Chun et al. (2005) proposed three branch line coupler using lumped distributed
elements. But, its bandwidth is only 1.1 GHz using -13 dB as standard level. In 2012,
Nejad proposed a compact three branch line coupler which is 47 percent smaller than
conventional one. Even though the size is 47 percent compact, its bandwidth
performance is only 1 GHz at – 13 dB, which is consider as narrower band. Chun et
al. (2006) proposed a compact four branch line coupler modified by using lumped
distributed element. However, its bandwidth is only 1.4 GHz.
In this research, the main interest is to design and produce a prototype, which is
able to operate in wider operating frequency range (1 GHz - 5 GHz). The purpose is
to reduce the power loss, less than – 13 dB or lower during the prototype’s operation
within a wider operating frequency. Also, a more compact prototype is produced for
making it more portable in modern consumer market, by using the slow wave
structure (SWS) and meandering lines (ML). Its S-parameters performance such as
return loss |S11|, through |S21|, coupling |S31| and isolation |S41|, measured in dB
(Decibel), remains the same, or, even better than conventional design performance.
4
1.3 Problem Statement
Conventional branch line coupler has narrow band characteristics and requires
larger circuit area in its fabrication process, especially for the coupler which is
operating at lower frequency (< 2 GHz). The cascaded method is able to increase the
operating bandwidth. However, such method might increase the size of the coupler. It
is an undesired scenario in MMIC (Monolithic Microwave Integrated circuit)
production, which is requiring a more compact spacing in circuit fabrication.
Also, modern consumers are expecting electrical apparatus that is more
portable. Bigger prototype area can also increase its fabrication cost. Hence, the slow
wave structures (SWS) and meandering lines (ML) technique are implemented in
prototype design in order to solve the above problems. Slow wave structure (SWS)
would be able to shortening the coupler branch lines, whereas, and the folding
approach of meandering lines could reducing the area occupying by a narrow
microstrip lines.
1.4 Objectives of the study
The main objectives of the research are
(1) To develop compact directional couplers, which are modified from three branch
line coupler (180 º) and four branch line coupler (270 º).
(2) To design and fabricate a prototype, which is able to operate in wider operating
frequency range (1.5 GHz – 3.5 GHz) and lower frequency (1 GHz - 5 GHz).
(3) To miniaturize conventional coupler using slow wave structure (SWS) and
meandering techniques (ML) at its branch lines area.
(4) To study the S-parameters measured in dB (Decibel) of the prototype for ensuring
that the performances of prototypes are validate for wideband operation.
5
1.5 Scope of the project
In this study, the wideband compact branch line couplers were developed.
Three branches and four branches were applied on the quadrature branch line coupler
in order to achieve the wider operating bandwidth. A slow wave structure (SWS) and
meandering lines (ML) techniques are applied on the branch line parts of the
designed couplers in order to miniature the size of the couplers. Both techniques did
reduce the area occupied by the fabricated prototype.
The modified prototypes are designed using 2.4 GHz as the center frequency.
TX Line program calculator was used to roughly determine the dimensions of the
microstrip line of the coupler. A Microwave Office (AWR) simulator was used to
re-exam the performance of the couplers with first draft dimensions. From the
simulation results, a minor corrections of the dimensions for the couplers have been
made to achieve the desired performances with 1.4 GHz bandwidth (Operating
frequency: (1.6 GHz to 3 GHz), return loss, |S11| better than –13 dB and its size turns
50 % smaller than conventional branch line couplers. The performance is considered
acceptable within the wide operating frequency range (1.5GHz – 3.5 GHz).
The prototypes were fabricated and measured using Vector Network Analyzer
(VNA) within the range of 1 GHz to 5 GHz. The measured performance of the
prototype couplers were analysis and compared to the simulation results based on the
return loss, |S11|, insertion loss, |S21|, coupling, |S31|, isolation, |S41| and phase balance
(90º± 2º), respectively for determining its validity. From the results comparison, the
simulation and measured results show good agreement even though there is minor
deviation of 1 to 5 %.
6
1.6 Report Organization
This research thesis consists of five chapters overall. Chapter 1 as an
introduction, it describes the problem statement, objectives of research, and scope of
project. Some background of quadrature hybrid and branch line directional coupler
will be discussed.
Next, chapter 2 will describe some basic historical background of directional
coupler theory development that leads to development of miniaturize directional
coupler. Also, the characteristics of the coupler especially its parameters are
described in detail. Besides, various type branch line couplers and approaches of
miniaturization are discussing in detail within this chapter.
In chapter 3, it discusses the research process or methodology involved in
completing the research project. The design specifications of a conventional coupler
and modified coupler will be described in detail. It also includes the design
dimensions, process and material specifications used.
Chapter 4 will present a report about the results of the measurement, analysis
and discussion of research project. Also, the measurement and evaluation of variables
method is analyst and explained. Simulation and measurement results of
S-parameters, in graph, are also included. The measured results will be used to
compare with simulation results. The purpose is to double confirm of its validity.
Finally, chapter 5 summarized all about multi-branch branch line coupler
project, objectives achieved and the conclusion of the research project, suggestion of
future work and its future prospect.
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