MILIMETER-WAVE BANDPASS FILTER FOR RADIO OVER FIBER APPLICATION

SITI NAJWA BINTI MUHAMMAD

UNIVERSITI TEKNOLOGI MALAYSIA

MILIMETER-WAVE BANDPASS FILTER FOR RADIO OVER FIBER APPLICATION

SITI NAJWA BINTI MUHAMMAD

A project report submitted in partial fulfilment of the

requirements for the award of the degree of

Master of Engineering (Electrical – Electronics & Telecommunications)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

JUNE 2014

iv

To my beloved family and friends

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ACKNOWLEDGEMENT

I wish to express my appreciation to my supervisor, Associate Prof. Dr. Razali

bin Ngah for advices and supports for completion of this project. I am also very thankful

to Zulkifli bin Ambak, an industry PhD candidate from Telekom Research and

Development Sdn Bhd (TM R&D) for giving full guidance, supports and sharing his

research experience to me.

I also would like to thank my fellow postgraduate students that have been

supportive in sharing ideas, thoughts and giving assistance at various occasions. I am

very grateful to all my family members for giving endless encouragement to me in

completing this project. Not forgetting my immediate reporting supervisor at work,

Muhamad Hafiz bin Senin at Packet One Networks (Malaysia) Sdn Bhd., for his

understanding and also fellow colleagues for words of encouragement. Thank you to all.

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ABSTRACT

Radio over fiber (RoF) technology is a promising option to deliver high speed

broadband networks as it capable of delivering high data rate transmission, has low

attenuation, immune to radio frequency interference (RFI) and simple design of remote

antenna unit (RAU). Milimeter-wave on the other hand is in the range 30 GHz to 300

GHz and offers higher bandwidth compared to lower RF frequency. The adoption of

millimeter-wave in RoF technology will enhance its ability to deliver high speed

broadband by utilizing the benefits of RoF and millimeter-wave. Millimeter-wave

bandpass filter has been design in this project for frequency range of 40 GHz to 42 GHz

as part of the RAU design. The designed bandpass filter will be fabricated using low

temperature co-fired ceramic (LTCC) technology that will enable compact and flexible

bandpass filter design.

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ABSTRAK

Teknologi radio melalui fiber merupakan satu alternatif yang baik untuk

penghantaran jalur lebar berkelajuan tinggi, di mana ia mampu menghantar data pada

kadar transmisi yang tinggi, mempunyai pengecilan isyarat yang rendah, imun kepada

gangguan isyarat frekuensi radio dan rekabentuk unit antena yang lebih ringkas (RAU).

Gelombang milimeter adalah pada julat frekuensi di antara 30 GHz dan 300 GHz, dan

menawarkan jalur lebar yang lebih tinggi berbanding yang ditawarkan oleh frekuensi

RF. Penggunaan gelombang millimeter dalam teknologi radio melalui fiber akan

meningkatkan kebolehannya untuk menghantar jalur lebar berkelajuan tinggi dengan

memanfaatkan kelebihan radio melalui fiber dan gelombang millimeter. Penyaring

‘bandpass’ gelombang millimeter telah direka dalam projek ini pada julat frekuensi

antara 40 GHz dan 42 GHz yang merupakan sebahagian daripada unit antena. Penyaring

yang telah direka ini akan difabrikasi menggunakan teknologi ‘low temperature co-fired

ceramic (LTCC)’ yang akan membolehkan rekaan penyaring ‘bandpass’ yang lebih

kompak.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION i-iii

DEDICATION Iv

ACKNOWLEDGEMENT v

ABSTRACT vi

ABSTRAK vii

TABLE OF CONTENTS viii-ix

LIST OF TABLES x

LIST OF FIGURES xi-xii

LIST OF ABBREVIATIONS xiii

LIST OF SYMBOLS xvi

1 INTRODUCTION

1.1 Project Overview 1

1.2 Problem Statement 3

1.3 Objective 4

1.4 Scope of Work 4

1.5 Thesis Outline 4

2 LITERATURE REVIEW

2.1 Introduction 6

2.2 Radio over Fiber 7

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2.3 Milimeter-wave 13

2.4 Bandpass Filter 15

2.5 Bandpass Filter Design Method 17

2.6 Related Research 22

2.7 Summary 26

3 METHODOLOGY

3.1 Introduction 27

3.2 Project Methodology 28

3.3 BPF Specification 30

3.4 BPF Design Methodology 30

3.5 Advanced Design System Software 34

3.6 Summary 35

4 RESULTS AND DISCUSSIONS

4.1 Introduction 36

4.2 ADS Simulation Configuration 36

4.3 Layout Realization Using ADS 38

4.4 Simulation Result and Discussion 39

4.5 Design Optimization by Parameterized

Analysis Method 40

4.6 Filter Optimization Result 47

4.7 Summary 49

5 CONCLUSION

5.1 Conclusion 50

5.2 Future Works 51

REFERENCES 52-54

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LIST OF TABLES

TABLE NO. TITLE PAGE

3.1 Proposed BPF design specifications 30

3.2 Values of J-inverter constant 31

3.3 Values of susceptance associated with J-inverter 32

3.4 Values of electrical length 32

3.5 Values of coupling capacitance Cg 32

3.6 Values coupling gap, S and shunt capacitances, Cp 33

3.7 Values coupling gap, S and shunt capacitances, Cp 33

3.8 Values of physical length of resonator 33

4.1 Dimension of filter elements for initial filter model and

optimized filter model

48

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Schematic Structure of a RoF system 8

2.2 Block Diagram of CS and RAU 8

2.3 In Builidng DAS architecture 9

2.4 Architecture of ROF with an optical WDM MAN 10

2.5 A bandpass filter frequency response 15

2.6 Two port network showing network variables 16

2.7 General microstrip structure 19

2.8 General configuration of end-coupled microstrip bandpass

filter

20

2.9 Immittance inverters comprised of lumped and

transmission line elements

20

2.10 Microstrip gap 22

3.1 Process flow of the proposed BPF design, simulation and

fabrication

29

3.2 Preliminary BPF layout 34

3.3 ADS layout window 35

4.1 Substrate layer configuration 37

4.2 Layout layer configuration 38

4.3 BPF side view 39

4.4 Simulation layout 39

4.5 Simulation result 40

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4.6 Simulated result of S11 and S21 with increase of L1 and

L3

41

4.7 Simulated result of S11 and S21 with decrease of L1 and

L3

42

4.8 Simulated result of S11 and S21 with increase of L2

length

42

4.9 Simulated result of S11 and S21 with decrease of L2

length

43

4.10 Simulated result of S11 and S21 with increase of S01 and

S34 length

44

4.11 Simulated result of S11 and S21 with decrease of S01 and

S34 length

45

4.12 Simulated result of S11 and S21 with increase of S12 and

S23 with increase length

46

4.13 Simulated result of S11 and S21 with increase of S12 and

S23 with decrease length

46

4.14 Optimized filter layout in ADS 47

4.15 Simulation result of the optimized filter 48

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LIST OF ABBREVIATIONS

ADS - Advanced Design System

BPF - Bandpass Filter

CS - Control Station

DAS - Distributed Antenna System

dB - Decibel

FBW - Fractional Bandwidth

FSIW - Folded Substrate Integrated Waveguide

GHz - Gigahertz

HD - High Definition

IF - Intermediate Frequency

IL - Insertion Loss

LTCC - Low Temperature Co-fired Ceramic

LTE - Long Term Evolution

MAN - Metropolitan Area Network

MIMO - Multiple-input-multiple-output

MMF - Multimode Fiber

POF - Polymer Optical Fiber

QAM - Quadrature Amplitude Modulation

RAU - Remote Antenna Unit

RF - Radio Frequency

RFI - Radio Frequency Interference

RL - Return Loss

RN - Remote Node

RoF - Radio over Fiber

SIW - Substrate Integrated Waveguide

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SMF - Single Mode Fiber

TEM - Transverse Electromagnetic

THz - Terahertz

VSWR - Voltage Standing Wave Ratio

WDM - Wavelength-division Multiplexing

WiFi - Wireless Fidelity

WiMAX - Worldwide Interoperability for Microwave Access

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LIST SYMBOLS

Sij - S parameters

b - Reflected waves

a - Incident waves

gn - Element of ladder type lowpass prototype with a normalized cut

off Ωc=1

Jj,j+1 - Characteristic admittances of J-inverters

Y - Characteristic admittance of microstrip line

Π - PI

Bj,j+1 - Series-capacitance discontinuities of susceptance

Δlje1,e2 - Effective lengths of shunt capacitances on both ends of resonator j

λg0 - Guided wavelength

ω - Angular frequency

l - Physical length of resonators

Cgj,j+1

- Coupling capacitances

Cpj j+1 - Shunt capacitances

CHAPTER 1

INTRODUCTION

1.1 Project Overview

Internet has been extensively used nowadays, in line with the growth of mobile

devices and applications which were facilitate by wired and wireless high speed

broadband networks. As the subscribers increased, the bandwidth will be on demand and

it would be not enough to cater subscribers’ data usage at one time. High speed

broadband networks are deployed either using wired or wireless medium. The wireless

high speed broadband networks include the Enhanced Data Rates for GSM Evolution

(EDGE), third generation (3G), High Speed Packet Access (HSPA), Worldwide

Interoperability for Microwave Access (WiMAX) and Long Term Evolution (LTE)

protocol. These wireless networks use the spectrum as its communication medium,

which is subject to regulatory guidelines. Fiber to the x (FTTX) also has been widely

deployed as a wired high speed broadband network. In FTTX, optical fiber has been

used to provide all or part of the local loop for last mile telecommunications. The last

mile could be to the home, desktop, node, cabinet, premises, building or telecom

enclosure. Both wired and wireless has its’ own benefits and also challenges.

2

The benefits of wireless network are the installation process is simple and fast

compared to wired networks and it provides mobility to users. However, as the usage

increase, the spectrum has become more congested, and the users are also exposed to

radio frequency interference (RFI).

Optical fiber networks carry high bandwidth data at equal upstream and

downstream specification, without much limitation on distances due to its low

characteristics. However, the challenging part is the installation work because fiber

optics are usually installed underneath streets or ground which took long period to

complete and involve high cost budget.

Radio over fiber (RoF) is a technology whereby light is modulated by radio

signal and transmitted over an optical fiber link to facilitate wireless access. The

transmitted signal over the fiber link could be in the form of various protocols such as

3G and WiFi and it can be simultaneously received by the same antenna. These signals

were sent to a central station (CS) where the light signals will be converted to radio

signals by remote antenna unit (RAU), amplified and retransmitted through wireless

medium by an antenna. Hence, frequency conversion is not required at base stations,

resulting simpler remote antenna unit design.

RAU is connected to CS. RAU consist of photodiode, laser diode, bandpass filter

(BPF), amplifier and antenna. Main function of RAU is to convert optical signal to

wireless, done by photodiode or vice versa, which is done by laser diode. The BPF

function is to pass frequencies within a certain range and attenuates frequencies outside

the range. Various studies had been conducted on the BPF design for the millimeter-

wave applications. The design includes the end-coupled, hairpin, substrate integrated

waveguide (SIW) and stripline parallel coupled filter topologies.

The limited availability of radio frequency (RF) bands requires utilization of

other frequency region and millimeter-wave is a good option because of the wide

bandwidths available to support high speed transmission. The millimeter-wave spectrum

is at 30GHz-300GHz frequency range.

This project is to study the millimeter-wave BPF design for radio over fiber

(RoF) remote antenna unit (RAU) application. The design will then be fabricated using

low temperature co-fired ceramic (LTCC) technology. Hence, as part of the millimeter-

3

wave adoption in RoF technology, this project has been narrowed down to design the

BPF.

1.2 Problem Statement

Internet access is very limited in rural areas due to its geographical factor. It is

not economical to connect end-user premises using fiber optic link due to the cost of

installing the fiber optic cable and cost of the fiber optic itself. RoF has been seen as a

suitable option to replace fiber optic link to reduce the cost of providing internet access

to rural areas.

To meet the high bandwidth transmission provided by fiber optic, the usage of

millimeter-wave will provide capacity close to what has been offered by conventional

fiber optic link. RoF operating in millimeter wave frequency has been proposed to

ensure high capacity data can be provided to end-user.

RoF system provides a simpler RAU, whereby the modulation of millimeter-

wave is done at CS. RAU consist of a photodetector, bandpass filter, amplifier and

antenna. This project scope has been narrowed down to propose a millimeter wave BPF

design for RoF system using LTCC technology. LTCC enables compact circuit

implementation that shall reduce the BPF size and this will produce a simpler and

compact RAU.

4

1.3 Objective

The objective of this project is to design, simulate and fabricate a downlink

millimeter-wave BPF for RoF technology using LTCC technology.

1.4 Scope of Work

The following scope of work will be the guideline during the process of the proposed

BPF development work:

i. The BPF topology that will be use is the end-coupled half wavelength resonator

bandpass filter.

ii. The BPF will use Chebyshev response to get the sharpest frequency cut-off.

iii. The proposed filter will be design for downlink in frequency range of 40 GHz to

42 GHz.

iv. Simulation will be done using Advanced Design System (ADS) software.

v. Fabrication technology is LTCC.

1.5 Thesis Outline

This thesis is a document for master project in Electrical Engineering –

Electronic and Telecommunication. The report is organized in the following manner.

5

Chapter 1 describes the project introduction covering project overview, problem

statement, objective and scope of work during project development.

Chapter 2 summarized the literature review which consists of studies in the radio

over fiber (RoF) technology, millimeter-wave properties and applications, microwave

bandpass filter design method and low temperature co-fired ceramic (LTCC)

technology.

Chapter 3 covers on the project methodology whereby detailed of the project

development processes will be further spell out to realize the objective of this project.

Chapter 4 covers on the simulation results and discussions. Simulation

configuration is also included in this chapter.

Chapter 5 concludes the simulation findings and proposed future works to

improve the filter design.

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54

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