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 syaratsyarat 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)
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 :...
To my beloved Mother and Family v
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 S 11 and S 21 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 S 11 dan S 21 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 STATUS REPORT FORM STUDENT DECLARATION SUPERVISOR DECLARATION DEDICATION ACKNOWLEDGEMENT ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURE LIST OF ABBREVIATION LIST OF APPENDIXES i ii iii iv v vi vii viii ix xiii xiv xv 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 Q e and M ij values 44 4.3 Spacing for n=4 combline filter 46 4.4 S 11 & S 21 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 S 21 (deg) Vs Frequency 38 3.6 Q e Vs Spacing 39 3.7 S 21 (db) Vs Spacing 40
xv 3,8 M Vs Spacing 40 3,9 Project Flow Chart 42 4.1 Q e Vs Spacing 44 4.2 M Vs Spacing 44 4.3 EM structure of n=4 combline filter 46 4.4 S 21 and S 11 simulated values 48 4.5 S 21 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- ISM band- Frequency Redundant 4 board Industrial, Scientific and Medical Band ADS- Advanced Design System
xvii LIST OF APPENDIXES NO A B C D E F G H I CONTENT Element value for Chebyshev lowpass prototype Graph of Attenuation Vs normalized Frequency Element Values for Chebyshev Lumped Element Calculation Quality Factor and Coupling Coefficient Calculation Design of Microwave Filter Characteristic of Coupled Microstriplines Gantt Chart 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 microwavefrequency 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 Design Simulation Fabrication 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.
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 S 21. On many occasions, an amplitude-squared transfer function for a lossless passive filter network is define as [1]. 2 1 S 21( j ) (2.1) 2 2 1 ( ) F n Where ε is a ripple constant, F n (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= Ω c 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 L AR =3.01dB at the cutoff frequency Ω c =1 is given by 1 ( (2.2) 1 2 S21 j ) 2n 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 Ω c. 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]. 2 1 S 21( j ) (2.3) 2 2 1 ( ) T n Where the ripple constant ε is related to a given passband ripple L AR in db by T n (Ω) is a chebyshev function of first kind of order n, which is defined as T n (Ω)= Tn ( ) cos( ncos 1 ) cosh( ncos 1 ) 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].