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i
Simulation and Analysis of Defected Ground Structure (DGS) as a Quarter
Wavelength at 2.4 GHz band
LIM YAN CHINN
This report is submitted in partial fulfillment of the requirements for award of Bachelor
of Electronic Engineering (Telecommunication Electronics) With Honours
Faculty of Electronic and Computer Engineering
Universiti Teknikal Malaysia Melaka
May 2011
ii
UNIVERSTI TEKNIKAL MALAYSIA MELAKA FAKULTI KEJURUTERAAN ELEKTRONIK DAN KEJURUTERAAN KOMPUTER
BORANG PENGESAHAN STATUS LAPORAN
PROJEK SARJANA MUDA II
Tajuk Projek : Simulation and Analysis of DGS as quarter wavelength at 2.4GHZ ………………………………………………………………………………
Sesi
Pengajian : 1 0 / 1 1
Saya ………LIM YAN CHINN……………………………………………………………………
(HURUF BESAR)
mengaku membenarkan Laporan Projek Sarjana Muda ini disimpan di Perpustakaan dengan syarat-
syarat kegunaan seperti berikut:
1. Laporan adalah hakmilik Universiti Teknikal Malaysia Melaka.
2. Perpustakaan dibenarkan membuat salinan untuk tujuan pengajian sahaja.
3. Perpustakaan dibenarkan membuat salinan laporan ini sebagai bahan pertukaran antara institusi
pengajian tinggi.
4. Sila tandakan ( √ ) :
SULIT*
*(Mengandungi maklumat yang berdarjah keselamatan atau
kepentingan Malaysia seperti yang termaktub di dalam AKTA
RAHSIA RASMI 1972)
TERHAD**
**(Mengandungi maklumat terhad yang telah ditentukan oleh
organisasi/badan di mana penyelidikan dijalankan)
TIDAK TERHAD
Disahkan oleh:
__________________________ ___________________________________
(TANDATANGAN PENULIS) (COP DAN TANDATANGAN PENYELIA)
Tarikh: ……………………….. Tarikh: ………………………..
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“I hereby declare that this report is the result of my own work except for quotes as cited
in the references.”
Signature :
Author : LIM YAN CHINN
Date :
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I hereby declare that I have read this report and in my opinion this report is sufficient in
terms of the scope and quality for the award of bachelor of Electronic Engineering
(Industrial Electronics) With Honours.”
Signature :
Supervisor’s Name : En. NOOR AZWAN SHAIRI
Date :
v
Dedicated to my beloved family especially my father and mother, lecturer, and also to
all my friends
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ACKNOWLEDGEMENT
First and foremost, I would like to praise God for His blessing. He gave me
physical and mental strength to carry on my final year project up to completion.
I would like to express gratitude and thanks to my supervisor, Mr. Noor Azwan
Shairi for his support and unfailing patience throughout the duration of the project. His
encouragement and guidance are truly appreciated. Otherwise, this project has not been
possible. I have learnt a lot under her guidance, be it practically or theoretically.
Other than that, I am also grateful to my all friends who help me and giving me
opinion along implementation of this project.
I would like to thanks my parents on their moral support as I can count on them
whenever I am upset or down.
Finally, I would like to offer thanks and deepest gratitude from the bottom of my
heart for all the support, encouragement and inspirations I obtained throughout the
duration of this project. The help rendered to me priceless, be it from the smallest of its
kind to the largest.
vii
ABSTRACT
DGS which is known as defected ground structure has been an increasing interest
in studying microstrip lines with various etched defect on ground plane that prohibit
wave propagation in certain frequency bands. The proposed DGS unit structure can
provide the band gap characteristic in some frequency bands with only one or more unit
lattice. By using a simple circuit analysis method, the equivalent circuit parameters are
extracted. By employing the extracted parameters and circuit analysis method, the band
gap effect for the provided defected ground structure can be explained. The low pass
filters can be designed and implemented by using the derived and extracted equivalent
circuit and parameter. Lastly, the overall results are an efficient and accurate means to
produce the complete equivalent models of DGS circuit for the design of various RF,
and microwave circuit which may require the high accurate design procedures.
viii
ABSTRAK
DGS dikenali sebagai berpaling tadah struktur bawah telah menjadi satu faedah
yang meningkatkan minat dalam belajar baris-baris mikrojalur dengan menjelma
pelbagai jenis kecacatan bergores pada satah bumi yang melarang perambatan
gelombang dalam kumpulan-kumpulan frekuensi tertentu. Struktur unit DGS yang telah
dicadangkan boleh menyediakan jurang jalur biasa dalam beberapa jalur-jalur frekuensi
dengan hanya satu atau lebih kekisi unit. Kaedah analisis litar mudah telah digunakan
bagi mengenal pasti parameter litar adalah setara dan berpaling tadah struktur bawah
dapat dijelaskan. Penapis lulus rendah boleh direka serta dilaksanakan dengan
menggunakan terbitan dan mengambil litar setara serta parameter. Akhir sekali,
keputusan secara keseluruhan adalah cekap dan tepat bagi menjanakan model-model
setara lengkap litar DGS dengan memperkenalikan pelbagai jenis bentuk radio
frequenksi , dan gelombang mikro litar yang memerlukan prosedur-prosedur reka bentuk
tepat tinggi itu.
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TABLE OF CONTENTS
CHAPTER TITLE PAGE
PROJECT TITLE i
BORANG PENGESAHAN STATUS LAPORAN ii
STUDENT DECLARATION iii
SUPERVISORY DECLARATION iv
DEDICATION v
ACKNOWLEDGEMENT vi
ABSTRACT vii
ABSTRAK viii
TABLE OF CONTENTS ix
LIST OF TABLES xiii
LIST OF FIGURES xiv
LIST OF ABBREVIATION xvii
I INTRODUCTION
1.1 Background 1
1.2 Objective 2
1.3 Problem Statement 2
1.4 Scopes Of Project 2
1.5 Methodology 3
x
II LITERATURE REVIEW
2.1 Introduction 4
2.2 DGS Unit Cell 6
2.3 Equivalent circuit of DGS 7
2.4 DGS as a Quarter Wavelength 9
2.5 DGS Characteristic 10
2.6 Smith Chart 11
2.7 Scattering Parameter 14
2.8 Application of DGS 16
III METHODOLOGY
3.1 Methodology 17
3.2 Flow Chart Diagram 18
3.3 DGS Simulation 20
3.4 Schematic Design 21
3.5 Layout Design 26
3.6 Transmission Line Design 27
3.7 Defected Ground Structure (DGS) Layout Design 27
IV RESULT AND ANALYSIS
4.1 Introduction 31
4.2 Analysis of LC Circuit (Circuit Simulation) 31
4.3 Quarter wavelength Circuit 36
4.4 Parallel RLC equivalent circuit 38
4.5 Parallel LC in series with R equivalent circuit 39
4.6 DGS Layout Design (EM Simulation) 41
4.6.1 Influence of the Square Lattice Dimension 41
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4.6.2 Influence of the Gap Distance 44
4.6.3 Influence of the Slot Wide 47
4.6.4 Influence of the Length of Slot 50
4.7 General Circuit Model for DGS 53
4.7.1 Influence of Electrical Length, E 53
4.7.2 Influence of Impedance, Z 55
V CONCLUSION AND RECOMMENDATION
5.1 Conclusion 57
5.2 Recommendation 58
REFERENCES 59
xii
LIST OF TABLES
NO TITLE PAGE
4.1 Result of influence square lattice dimension 43
4.2 Result of influence gap distance 46
4.3 Result of influence slot wide 49
4.4 Result for the Influence of length of slot 52
4.5 Result with different value of electrical length, E 54
4.6 Result with different value of impedance, Z 56
xiii
LIST OF FIGURES
NO TITLE PAGE
2.1 Different types of DGS 5
2.2 Dumbbell shapes of DGS 6
2.3 LC equivalent circuits of Dumbbell DGS 7
2.4 RLC equivalent circuits of Dumbbell DGS 8
2.5 π Shaped equivalent circuits 9
2.6 The fast wave and slow wave that comprise the model waveform 11
2.7 An impedance Smith chart 12
2.8 S Parameter Two Port Model 14
3.1 Flow Chart Diagram 18
3.2 ADS software 20
3.3 Creating Project 22
3.4 Creating Design (Schematic) 22
3.5 Equivalent circuit used in Schematic (ADS) 23
3.6 Example of Smith Chart used in ADS 23
3.7 Band stop filter frequency response 24
3.8 DGS layout as example 24
3.9 Values for Inductor and Capacitor can be tuned after the setting 25
has been done
3.10 Tune parameter which used to vary values of components 25
3.11 Design and analysis method of dumbbell DGS 26
3.12 Substrate setup and Layers mapping 28
3.13 Port Editor 28
xiv
3.14 S-parameter momentum simulation 29
3.15 Momentum simulation setup 29
3.16 (a) Component library (b) Choose the layout component from the library 30
3.17 Schematic layout looks like of DGS 30
4.1 LC equivalent circuit 31
4.2 Simulation result 32
4.3 Simulation result in Smith Chart of S(1,1) 33
4.4 S(1,1) Phase response 33
4.5 Results of S(1,1) showing different values of frequency when value 34
of Inductor is varied
4.6 Results of S(1,1) showing different of phase response when value 34
of Inductor is varied
4.7 Results of S(1,1) showing different values of frequency when value 35
of Capacitor is varied
4.8 Results of S(1,1) showing different of phase response when value 35
of Capacitor is varied
4.9 Quarter wavelength Circuit 36
4.10 Simulated S(1,1) of Phase Response 37
4.11 Smith Chart shows Short to Open 37
4.12 Parallel RLC equivalent circuit 38
4.13 Simulated S(1,1) of Phase responses 38
4.14 Simulated S(1,1) 39
4.15 Parallel LC Series with R equivalent circuit 39
4.16 Simulated S(1,1) 40
4.17 Simulated S(1,1) of phase response 40
4.18 EM Simulation for DGS unit cell 41
4.19 Simulated S(1,1) for the proposed DGS 42
4.20 Simulated S(1,1) which the markers marked at open circuit 42
4.21 Simulated S(1,1) which the markers marked at 2.4 GHz 43
4.22 EM Simulation for DGS unit cell 44
4.23 S(1,1) Phase response 44
xv
4.24 Simulated S(1,1) which the markers marked at open circuit 45
4.25 Simulated S(1,1) which the markers marked at 2.4 GHz 45
4.26 EM Simulation for DGS unit cell (Bottom view) 47
4.27 S(1,1) Phase response 47
4.28 Simulation result of S(1,1) in Smith Chart which the markers 48
marked at open circuit
4.29 Simulation result of S(1,1) in Smith Chart which the markers 48
marked at 2.4 GHz
4.30 EM Simulation for DGS unit cell (Bottom view) 50
4.31 S(1,1) Phase response 50
4.32 Simulation result of S(1,1) in Smith Chart which the markers 51
marked at open \circuit
4.33 Simulation result of S(1,1) in Smith Chart which the markers 51
marked at 2.4 GHz
4.34 Circuit Model for DGS 53
4.35 S(1,1) Phase response 53
4.36 Simulation result of S(1,1) in Smith Chart at 2.4 GHz 54
4.37 Circuit Model for DGS 55
4.38 S(1,1) Phase response 55
4.39 Simulation result of S(1,1) in Smith Chart at 2.4 GHz 56
xvi
LIST OF ABBREVIATION
DGS Defected Ground Structure
PBG Photonic band-gap
ADS Advanced Design System
EM Electromagnectic
RF Radio Frequency
AC Alternating Current
MW Microwave
3D Three Dimensions
TL Transmission Line
1
CHAPTER I
INTRODUCTION
1.1 Background
In past few years, Defected Ground Structure (DGS) has played an
important role in radio frequency/microwave circuits. The first defected ground
structure was proposed in 1999 which based on the idea of photonic band-gap
(PBG) structure and its application can be found in the design of planar circuits
and low pass filter [1]. However, it is difficult to use a PBG structure for the
design of microwave components due to the difficulties of the modeling. Another
difficulty in using the PBG circuit is caused by the radiation from the periodic
etched effects [5]. A DGS is where the ground plane metal is purposely modified
with certain geometry to enhance performance. A variety of slot geometry is
realized by etching a defective pattern in the ground plane which disturbs the
shield current distribution in the ground plane. It can also be used in various
circuits with antenna, filters, delay lines, phase shifters and so on [1].
The disturbance can change the characteristic of a transmission line, such
as equivalent capacitance or inductance to obtain the slow wave effect and the
band stop property [6]. In a word, any defect ground structure etched in the
ground plane of the microstrip can give rise to increasing effective capacitance
2
and inductance. In order to maintain the biasing line of DGS as a quarter
wavelength, physical width has to be wider and length is shorter than that of the
conventional bias line.
This project will further investigate the capability of DGS as a quarter
wavelength at 2.4 GHz band. It involves software called Advanced Design
System (ADS) to design and simulate the DGS.
1.2 Project Objective
The objective of this project is to do the parametric studies on the DGS as a
quarter wavelength by analyzing at the DGS equivalent circuit and layout.
1.3 Problem Statement
1. No detail parametric study on the phase response of DGS at quarter
wavelength [1,6,10,11].
2. Most of the technical papers focus on applications of DGS [5,7,9,17].
1.4 Scopes of Project
1. Design the DGS as quarter wavelength in ADS software as an equivalent
circuit and layout.
2. Simulate and analyze the DGS in equivalent circuit and EM simulation in
ADS software.
3
1.5 Methodology
This project consists of three stages. The literature review and
background study are done for the first stage such as the basic conceptions and
transmission characteristics of DGS. The equivalent circuit models of varieties of
DGS units are also presented. After finished the study, second stage will be
precede on the equivalent circuit and EM simulation by using Advanced Design
System (ADS). Next, simulation results are compared by analysis the phase
response of every change of parameters.
4
CHAPTER II
LITERATURE REVIEW
2.1 Introduction
Recently, there has been an increasing interest in studying microstrip
lines that prohibit wave propagation in certain frequency bands using defected
ground structure (DGS) [1,2,3,4,5,6]. Therefore, DGS is an etched periodic or
non-periodic cascaded configuration defect in ground of a planar transmission
line such as microstrip, coplanar and conductor backed coplanar waveguide
which disturbs the shield current distribution in the ground plane cause of the
defect in the ground. This disturbance will change characteristic of a
transmission line just like line capacitance and inductance [1].
. DGS can be realized by etching off a simple shape in the ground plane,
depending on the shape and dimensions of the defect, the shielded current
distribution in the ground plane is disturbed, resulting a controlled excitation and
propagation of the electromagnetic waves through the substrate layer. The shape
of the defect may be changed from the simple shape to the complicated shape for
the better performance [5].
5
Different shapes of DGS have been studied such as concentric ring circle,
spiral, dumbbells, elliptical and U- and V- slots. Every DGS shapes can be
represented as a circuit consisting of inductance and capacitance, which can
leads to a certain frequency band gap determined by the shape, dimension and
position of the defect. DGS gives an extra degree of freedom in microwave
circuit design and can be used for various types of applications [2].
Figure 2.1: Different types of DGS: (a) spiral head (b) arrow-head slot (c) “H”
shape slot (d) square open-loop with a slot in middle section (e) open loop
dumbbell (f) inter-digital DGS [1]
In RF circuit, DGS provides a significant advantage by extending its
applicability such in amplifiers, low pass filter, power dividers, couplers and RF
switch. Researchers of DGSs are interested in the area of extensive capability in
microwave circuit. The parameters of equivalent circuit model of DGSs were
also researched and utilized to design. Many passive and active microwave and
millimeter devices have been developed to suppress harmonics and realize the
compact physical dimensions of circuits for the design flow of circuits with DGS
comparatively simple [1].
6
2.2 DGS Unit Cell
Figure 2.2 Dumbbell shapes of DGS [1].
A unit DGS (dumbbell) section is created in the ground plane as show in
Figure 2.2 [5]. In many microwave circuits, the dumbbell shaped DGS pattern is
commonly adopted because easy and simple to design. The dumbbell DGS are
composed of two a x b rectangular defected areas, g x w gaps and narrow
connecting slot wide etched area in backside metallic ground plane as shown in
Figure 2.2 [1].
The DGS with the microstrip line employs and intentional defect on the
ground and it provides band stop characteristic from the resonance property. The
cut off frequency of the DGS is mainly dependent on the etched square area in
ground plane. There is an attenuation pole location, which is due to the etched
gap distance [1, 5].
An attenuation pole can be generated by combination of the inductance
and capacitance elements. The frequency characteristic of the DGS section can
be explained by varied the value of capacitor. The etched gap area, which is
placed under a conductor line, provides the parallel capacitance with effective
line inductance [1, 5, 7].
7
The proposed DGS section is fully describe by two parameters, they are
the etched lattice dimension and the gap distance. Thus, different types of shape
and slot geometries will affect the resonant frequency. Both of these will control
the fundamental resonant frequency and higher order resonances [6]. To fulfill
the different requirements, a variety of DGS shapes have evolved over time.
2.3 Equivalent circuit of DGS
Usually, design and analysis are two challenges for DGS. It is needed to
remove the equivalent circuit parameters by applying the proposed DGS section
to a practical circuit design example. In order to derive the equivalent circuit
parameters of DGS unit at the reference plane, the S-parameter versus frequency
should be calculated by full wave electromagnetic (EM) simulation to explain the
cutoff and attenuation pole characteristic of the DGS section. At present, DGS
can be equivalent by three types of equivalent circuits: (1) LC and RLC
equivalent circuits, (2) π shaped equivalent circuit, (3) quasi-static equivalent
circuit. For this project, the DGS will only use the LC and RLC equivalent
circuit as shown in Figure 2.3 and Figure 2.4 [1].
Figure 2.3: LC equivalent circuits of Dumbbell DGS [1].
8
The LC equivalent circuit of DGS with rectangular parts of dumbbell
DGS increase route length of current and the effective inductance. The effective
capacitor of the microstrip line can be increased by inserting a slot in the ground
surface to accumulate the charge. Two rectangular defected areas and one
connecting slot correspond to the equivalently added inductance (L) and
capacitance (C) respectively. A resonance will only occur at a certain frequency
because of the parallel LC circuit. As the etched area of the unit lattice increases,
the effective series inductance increase and increasing the series inductance gives
rise to a lower cut off frequency. When the etched gap distance increases, the
effective capacitance decreases so that the attenuation pole location moves up to
higher frequency [1].
Figure 2.4: RLC equivalent circuits of Dumbbell DGS [1].
DGS can be modeled by a parallel R, L and C circuit connected to
transmission lines at its both sides as shown in Figure 2.4 [1]. This resistance
corresponds to the radiation, conductor and dielectric losses in the defect. The
size of DGS is determined by accurate curve fitting results for equivalent circuit
elements to correspond exactly to the required inductance [1].
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