MICROSTRIP BANDPASS FILTER DESIGN (COMBLINE)
MOHAMAD HAMIZAN BIN TUAH
This report is submitted in partial fulfilment of the requirements for the award of
Bachelor of Electronic Engineering (Telecommunication Electronics) With Honours
Faculty of Electronic and Computer Engineering
Universiti Teknikal Malaysia Melaka
May 2009
UNIVERSTI TEKNIKAL MALAYSIA MELAKA
FAKULTI KEJURUTERAAN ELEKTRONIK DAN KEJURUTERAAN KOMPUTER
BORANG PENGESAHAN STATUS LAPORAN
PROJEK SARJANA MUDA II
Tajuk Projek : Microstrip Bandpass Filter Design (Combline)
Sesi
Pengajian : 2008/2009
Saya MOHAMAD HAMIZAN BIN TUAH
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)
Alamat Tetap: ……………………………......
……………………………......
Tarikh: ……………………….. Tarikh: ………………………..
√
iii
“I hereby declare that this report is result of my own effort except for the quotes
as cited in the references”
Signature : ................................................................
Name : MOHAMAD HAMIZAN BIN TUAH
Date : ................................................................
iv
“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 (Telecommunication Electronics) With Honors.”
Signature : ....................................................................
Name : MR. ABD SHUKUR BIN JA’AFAR
Date : ....................................................................
v
” To my beloved Mother and Family”
vi
ACKNOWLEDGEMENT
First of all, I would like to thank Allah SWT for giving me the strength to
endure and overcome the obstacles and difficulties throughout the process of
completing the projects and the report of my final year project.
I also want to express my gratitude towards Mr Abd Shukur Bin Ja’afar for
being very supportive and helpful in helping me with my project. It is with his
guidance and supervision that I have managed to complete this project in time.
To my beloved mother, thank you for being such a good example and a friend
to me. Your advice and action gives me strength to endure the challenges i have
faced. To my whole family and friends, thank you for your support, suggestions and
for all the help.
Last but not least, I would like to acknowledge any individual that has
contributed their energy and knowledge for my project.
vii
ABSTRACT
This project is about designing a wide bandpass microstrip filter that will
operate at the industrial, scientific and medical (ISM) band. The ISM band was an
unlicenced band which is originally reserved internationally for the use of RF
electromagnetic field for industrial, scientific and medical purposes other than
telecommunication. A bandpass microstrip filter working at the ISM band will reject
other frequency outside the ISM band. The design process will be started by
obtaining the order of the filter base on the specification given. Then, lumped
element bandpass filter will be designed. Next is the realization to microstrip
structure process. The dimension of microstrip such as the length, width and spacing
of the microstrip filter will be determined by using filter realization method.
Simulation was done by using Microwave Office software to observe the S11 and S21
of the filter. The next process is to fabricate the designed microstrip bandpass filter
on the FR4 boar and measurement will be done on the fabricated filter by using
network analyzer. The procedure, results and discussion were discussed in this
report.
viii
ABSTRAK
Projek ini adalah berkenaan dengan mereka bentuk sebuah penapis mikrojalur
lulus jalur lebar yang beroperasi pada jalur frekuensi Industrial, Scientific and
Medical (ISM). Jalur frekuensi ISM adalah jalur frekuensi yang tidak memerlukan
lesen dan dikhaskan secara global untuk kegunaan medan electromagnet frekuensi
radio untuk kegunaan industri, saintifik dan perubatan selain untuk kegunaan
telekomunikasi. Penapis mikrojalur lulus jalur yang beroperasi pada frekuensi ISM
akan bertindak menghalang frekuensi-frekuensi selain daripada frekuensi ISM.
Proses mereka bentuk sebuah penapis lulus jalur bermula dengan menentukan
bilangan peringkat penapis berdasarkan tentuan yang diberikan. Kemudian penapis
lulus jalur elemen gumpalan akan direka. Seterusnya adalah proses untuk merealisasi
kepada struktur mikrojalur di mana dimensi mikrojalur seperti panjang, lebar dan
jarak untuk penapis lulus jalur mikrojalur akan ditentukan dengan menggunakan
realisasi Simulasi dijalankan menggunakan perisian Microwave Office dimana nilai
S11 dan S21 akan diperhatikan. Proses seterusnya adalah proses fabrikasi penapis
mikrojalur lulus jalur diatas papan FR4 dan pengukuran akan dijalankan keatas
penapis yang telah siap dibina dengan menggunakan alat penganalisis rangkaian..
Tatacara, dapatan dan diskusi akan dibincangkan di dalam laporan ini.
ix
TABLE OF CONTENT
CHAPTER CONTENT PAGE
PROJECT TITLE i
STATUS REPORT FORM ii
STUDENT DECLARATION iii
SUPERVISOR DECLARATION iv
DEDICATION v
ACKNOWLEDGEMENT vi
ABSTRACT vii
ABSTRAK viii
TABLE OF CONTENTS ix
LIST OF TABLES xiii
LIST OF FIGURE xiv
LIST OF ABBREVIATION xv
LIST OF APPENDIXES xvi
x
I INTRODUCTION 1
1.1 Background Studies 2
1.2 Problem Statement 2
1.3 Objectives 3
1.4 Scope of Work 3
II LITERATURE REVIEW 5
2.1 The Microstrip Filter Concept 5
2.1.1 Transfer Function
2.1.1.1 General Definition 6
2.1.1.2 Butterworth Response 6
2.1.1.3 Chebyshev Response 7
2.1.2 LPP Filters & Elements 8
2.1.2.1 Butterworth LPP Filters 9
2.1.2.2 Chebyshev LPP Filters 10
2.1.3 Frequency & Element Tranformation 11
2.1.3.1 Lowpass Transformation 12
2.1.3.2 Highpass Transformation 13
2.1.3.3 Bandpass Transformation 13
xi
2.1.3.4 Bandstop Transformation 15
2.2 Network Analysis 16
2.2.1 Network Variable 16
2.2.2 Scattering Matrix 17
2.2.3 ABCD Parameter 18
2.3 FR-4 board 19
2.3.1 Specification 20
2.3.2 Advantages & Disadvantages 20
2.4 Transmission Line 21
2.4.1 Microstrip Lines 22
2.4.2 Coaxial Cables 23
2.4.3 Coupled Line 24
2.4.3.1 Theory of Coupled Line Couplers 25
2.5 Microstrip Filter Implementation 26
2.5.1 End-coupled half-wavelength resonator 26
2.5.2 Parallel-coupled half-wavelength resonator 27
2.5.3 Hairpin Filter 27
2.5.4 Interdigital Filter 28
2.5.5 Combline Filters 29
2.6 Coupled Rectangular Bars 33
III METHODOLOGY 34
xii
3.1 Block Diagram
3.1.1 Filter Specification 35
3.1.2 Lowpass Prototypes 36
3.1.3 Lumped Elements 36
3.1.4 Filter Realization 37
3.1.4.1 Filter Dimension 38
3.1.5 Simulation 41
3.1.6 Fabrication 41
3.2 Project Flow Chart 42
IV RESULTS & DISCUSSION
4.1 Filter Specification 43
4.2 Combline Filter Design 44
4.2.1 Lowpass Prototype Values 44
4.2.2 Determining The Dimension 44
4.2.3 Simulation 46
4.2.4 Analysis of result 48
V CONCLUSION & SUGGESTION 50
5.1 Conclusion 50
5.2 Suggestion and Recommendation 51
REFERENCE
APPENDIX
xiii
LIST OF TABLES
NO TITLE PAGE
2.1 Element values for Butterworth lowpass prototype 9
2.2 Transformation Table 12
3.1 g value for n=4 39
3.2 Transformation TableValues spacing and quality factor 39
3.3 Values spacing and coupling coefficient 40
4.1 g value for n=4 44
4.2 Qe and Mij values 44
4.3 Spacing for n=4 combline filter 46
4.4 S11 & S21 simulated values 48
4.5 -3dB value for simulated result 49
xiv
LIST OF FIGURE
NO TITLE PAGE
2.1 Chebyshev and Butterworth Response 7
2.2 LPP for all-pole filter 8
2.3 Microstrip line 22
2.4 Coaxial Cable 23
2.5 Coupled-line 24
2.6 Couple Line Coupler 25
2.7 End-Coupled half-wavelength resonator 26
2.8 Parallel-Coupled half-wavelength resonator 27
2.9 Hairpin Filter 27
2.10 Interdigital Filter 28
2.11 Combline Filter 29
2.12 Coupled Rectangular Bars Centered Between Parallel Bars 33
3.1 Block Diagram 34
3.2 Lowpass Prototype Filter 36
3.3 Lumped Element Bandpass Filter 37
3.4 Resonators Configuration to Determined Spacing 38
3.5 S21(deg) Vs Frequency 38
3.6 Qe Vs Spacing 39
3.7 S21(dB) Vs Spacing 40
xv
3,8 M Vs Spacing 40
3,9 Project Flow Chart 42
4.1 Qe Vs Spacing 44
4.2 M Vs Spacing 44
4.3 EM structure of n=4 combline filter 46
4.4 S21 and S11 simulated values 48
4.5 S21 cutoff values 49
xvi
LIST OF ABBREVIATION
LPP- Lowpass Prototypes
LPF- Lowpass Filter
HPF- Highpass Filter
BPF- Bandpass Filter
BSF- Bandstop Filter
S-parameter- Scattering Parameter
RF- Radio Frequency
FR-4 board- Frequency Redundant 4 board
ISM band- Industrial, Scientific and Medical Band
ADS- Advanced Design System
xvii
LIST OF APPENDIXES
NO CONTENT
A Element value for Chebyshev lowpass prototype
B Graph of Attenuation Vs normalized Frequency
C Element Values for Chebyshev
D Lumped Element Calculation
E Quality Factor and Coupling Coefficient Calculation
F Design of Microwave Filter
G Characteristic of Coupled Microstriplines
H Gantt Chart
I Technical Report
CHAPTER 1
INTRODUCTION
Filters play important roles in many RF/microwave applications including
cellular radio, satellite communication, and radar. They are used to separate or
combine different frequencies. The electromagnetic spectrum is limited and has to be
shared. Therefore, filters are used to select and confine the RF/microwave signals
within assigned spectral limits.
The first chapter of this report is the introduction part of the report. In this
chapter, the background studies, the problem statements, the objectives and the scope
of work will be discussed
2
1.1 Background Studies
The development of applications such as wireless communication s continue
to challenge RF/microwave filters with even more stringent requirement such as
higher performance, smaller size, lighter weight and lower cost. Depending on the on
the requirements and specifications and specifications, RF/microwave filters maybe
designed as lumped elements or distributed elements circuits and can be realized in
various transmission line structures, such as waveguide, coaxial line and microstrip.
Microstrip is a type of electrical transmission line which can be fabricated
using printed circuit board [PCB] technology, and is used to convey microwave-
frequency signals. It consists of a conducting strip separated from a ground plane by
a dielectric layer known as the substrate. Microwave components such as antennas,
couplers, filters, and power dividers can be formed from microstrip, the entire device
existing as the pattern of metallization on the substrate. Microstrip is thus far cheaper
than traditional waveguide technology, as well as being far lighter and more
compact.
1.2 Problem statement
The industrial, scientific and medical (ISM) band was originally reserved
internationally for the use of RF electromagnetic fields for industrial, scientific and
medical purposes other than communications. Therefore, a device is needed to filter
signals so that it will operate in this ISM band. Therefore, does microstrip filter fulfil
this requirement? Theoretically, microstrip filter can operate at high frequency and
microstrip filter is easy to fabricate. Therefore, the behaviour of microstrip filter will
be studied.
3
1.3 Objectives
The objectives of the project are:
i) To design and simulate a microstrip filter that will operate at 2.4 GHz
until 2.5GHz is suitable for the ISM band.
ii) To fabricate a microstrip combline bandpass filter on FR4 board by
using etching technique.
iii) To make a comparison between the result obtained by simulation and
the measured value.
1.4 Scope of Works
The scope of work of the project consists of three major parts which are the
design part, the simulation part, and the fabrication part.
1.4.1 Design
During the designing process, the number of order for the filter will be
determined based on the specification given. When the number of order has been
determined, the lowpass prototype for the filter will be design. Since the objective of
the project is designing a bandpass filter, transformation from lowpass filter to
bandpass filter will be done for the lowpass prototype.
Design Simulation Fabrication
4
1.4.2 Simulation
When the design process had been done, the simulation will be done on the
Advanced Design System (ADS) software and by using the Microwave Office
software. From simulation, the Scattering Matrix and the cut of frequency for the
bandpass filter can be observed.
1.4.3 Fabrication
When the results obtained from the simulation fulfil the requirement of the
filter, fabrication of the filter will be done. For the fabrication, etching technique was
used to fabricate the filter on the FR4 board. When the filter been fabricated, testing
will be done. Testing was done by using the network analyzer. Then comparison will
be made between the simulation and the measurement result obtained from the
network analyzer.
1.5 Report Structure
Chapter Content
I Introduction
II Literature Review
III Methodology
IV Result and Discussion
V Conclusion and Suggestion
CHAPTER 2
LITERITURE REVIEW
This chapter will discuss about the literature review used for my project. For
the project, some study had been done on the microstrip filters concept, the theory
implemented, and the technique used for this project.
2.1 The Microstrip Filters concept.
2.1.1 Transfer Fuctions
A transfer function is a mathematical representation, in terms of spatial or
temporal frequency, of the relation between the input and output of a system.
6
2.1.1.1 General definition
The transfer function of a two-port filter network is a mathematical
description of network response characteristics, namely a mathematical expression of
S21. On many occasions, an amplitude-squared transfer function for a lossless passive
filter network is define as [1].
)(1
1)(
22
2
21
nFjS (2.1)
Where ε is a ripple constant, Fn(Ω) represents a filtering or characteristic function
and Ω is a frequency variable. For convenience purposes, let Ω represent a radian
frequency variable of a lowpass prototype filter that has a cutoff frequency at Ω= Ωc
for Ω=1 (rad/s). Frequency transformations to the usual radian frequency for
practical lowpass, highpass, bandpass, and bandstop will be discussed later. [1]
2.1.1.2 Butterworth (Maximally Flat) response.
The amplitude-squared transfer function for Butterworth filters that have an
insertion loss LAR=3.01dB at the cutoff frequency Ωc=1 is given by
njS
2
2
211
1)( (2.2)
Where n is the degree or the order of the filter, which corresponds to the number of
reactive elements, required in the lowpass prototype filter. This type of response is
also referred to a maximally flat because its amplitude-squared transfer function has
the maximum number of (2n-1) zero derivatives at Ω=0. Therefore a maximally flat
approximation to the ideal lowpass filter in the passband is best at Ω = 0, but
deteriorates as Ω approaches the cutoff frequency Ωc. The Figure 2.1 shows the
typical maximally flat response. [1]
7
2.1.1.3 Chebyshev Response
The Chebyshev response that exhibits the equal-ripple passband and
maximally flat stopband is depicted in Figure 2.1. The amplitude-squared transfer
function that describes these types of response is [1].
)(1
1)(
22
2
21
nTjS (2.3)
Where the ripple constant ε is related to a given passband ripple LAR in dB by Tn(Ω)
is a chebyshev function of first kind of order n, which is defined as
Tn(Ω)=)1coscosh(
)1coscos()(
n
nTn
1
1 (2.4)
Hence, the filters realized from (2.3) are commonly known as Chebyshev filters. [1]
Figure 2.1 Butterworth (maximally flat) and Chebyshev lowpass response [4].
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