Microstrip array antenna for automobile radar system

(1)

MICROSTRIP ARRAY ANTENNA FOR AUTOMOBILE RADAR

SYSTEM

MAI ABDEL RAHMAN OSMAN

A thesis dissertation submitted in partial fulfillment of the requirements for the award of the degree of

Master of Electrical-Telecommunications Engineering

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

(2)

iii

To my dear beautiful mother, my dear decent father,

my beloved husband and my lovely daughter:

Thank you for your continuous Encouragement and deepest Support.

(3)

iv

ACKNOWLEDGEMENT

First of all, thanks to our creator, “Allah” for the continuous blessing and for

giving me the strength and chances in completing this project.

Special thanks to my project supervisor, Dr.Nor Hisham Bin Haji Khamis,

for his guidance and encouragement during this master project. I greatly appreciate

his care and dedication in constructively criticizing my work, including my thesis.

I would like to convey my deepest appreciation to the postgraduate students

Eng.Tellaha and my friend Siti Zurida Ibrahim, who have helped me by sparing

some times to share ideas that have nurtured my thoughts in the area of the project.

Gratitude is also extended to faculty of Electrical Engineering, Universiti

Teknologi Malaysia for the full support in this project.

I am profoundly grateful for my family especially my parents, who always

love me, believe in me, and support me, no matter where I am.

Finally, I wish to express my appreciation and thanks to my husband, Mohd.

Kabashi, whose unconditional support and caring is an indispensable source of my

(4)

v

ABSTRACT

Point to point communication brings a crucial responsibility to antennas

since they are expected to provide a transmission between those devices. The

Industry, Scientific and Medical (ISM) Band, Unlicensed with the range 2.4 - 2.4835

GHz is used as the operation band. In a high performance point to point application

where size, weight, cost, performance, ease of installation are constrains, a suitable

antenna is very much required. To meet these requirements, microstrip antenna is

usually preferred. Microstrip antennas are currently one of the fastest growing

segments in the telecommunications industry and promised to become the preferred

medium of telecommunication in the future. Although microstrip antenna has

several advantages, it also has several drawbacks such as low gain and narrow

bandwidth. These disadvantages can be overcome by constructing many patch

antennas in array configuration. This project focuses on the design of microstrip

patch antenna with operating frequency at 2.45GHz for automobile radar system.

The antenna is mainly intended to be used as receiving antenna and receives signals

transmitted from an automobile radar system in order to control the movement of the

car. An array design based on series fed configuration and consisting of four

rectangular patch elements was designed, simulated, fabricated and measured. These

elements are connected directly to the microstrip line at their corners and inclined 45

degree in order to achieve circular polarization. The simulation, fabrication and

measurement methods were accomplished with the aid of MathCAD, AWR

Microwave Office 2004, AutoCAD, FR4 Board, UV Equipment, Macroni Scalar

Analyzer 6204 and Anechoic Chamber. The design met the ISM BAND Standard

and able to operate in this Band. The fabricated array is found to have a variation in

the operating frequency from the simulation resonant frequency. Return loss results

of the fabricatd design have a value of -32.8dB with a bandwidth of 4.8%, which

could be considered as a narrow band width. This further strengthens the theory of

series feed configurations that arrays produce better return loss but narrower

(5)

vi

ABSTRAK

Komunikasi titik ke titik membawa tanggungjawab yang genting kepada

antena di mana ia diharapkan boleh menyediakan penghantaran antara peranti

penghantar dan peranti penerima. Jalur Industri, Saintifik dan Perubatan (ISM), yang

tidak berlesen dengan had antara 2.4 - 2.4835 GHz digunakan sebagai jalur operasi.

Dalam perlaksanaan titik ke titik berprestasi tinggi yang mana saiz, berat, kos,

prestasi dan pemasangan yang mudah menjadi kekangan, antena yang sesuai adalah

sangat diperlukan. Untuk memenuhi keperluan ini, antena mikrojalur biasanya

dipilih. Antena mikrojalur masa kini merupakan salah satu segmen yang

berkembang pesat dalam industri telekomunikasi dan menjanjikan medium yang

dipilih pada masa akan datang. Walaupun antena mikrojalur mempunyai beberapa

kelebihan, ia juga mempunyai beberapa kelemahan seperti gandaan yang rendah dan

lebar jalur yang sempit. Kelemahan ini boleh diatasi dengan menggabungkan banyak

antena tampalan dalam konfigurasi array. Projek ini memfokus kepada

merekabentuk antena mikrojalur tampalan dengan frekuensi operasi pada 2.45GHz

untuk sistem radar automobil. Antena ini pada pokoknya digunakan sebagai antena

penerima dan menerima isyarat yang dihantar dari sistem radar automobil supaya

pergerakan kereta dapat dikawal. Array yang direkabentuk berdasarkan kepada

konfigurasi suapan sesiri dan terdiri daripada empat element tampalan berbentuk

segi empat bujur telah direka, disimulasi, dihasilkan dan diukur. Elemen-elemen ini

telah disambungkan di pepenjuru secara terus ke garisan mikrojalur dengan 45

darjah bengkok untuk mencapai polarisasi bulat. Kaedah simulasi, pembuatan dan

ukuran telah disempurnakan dengan bantuan MathCAD, AWR Microwave Office

2004, AutoCAD,Papan FR4,Peralatan UV, Macroni Scalar Analyzer 6204 dan

Anechoic Chamber. Rekaan telah mencapai piawaian jalur ISM dan berupaya

beroperasi pada jalur ini. Array yang telah dihasilkan diperhatikan mempunyai

variasi pada frekuensi operasi berbanding dengan frekuensi gema yang disimulasi.

Kehilangan balikan yang diperolahi pada rekaan yang dihasilkan adalah sebanyak

-32.8dB dan mempunyai lebar jalur yang sempit sebanyak 4.8%. Ini menguatkan lagi

teori berkenaan konfigurasi suapan sesiri di mana array boleh menghasilkan

kehilangan balikan yang lebih baik tetapi mempunyai lebar jalur sempit berbanding

(6)

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITEL i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF SYMBOLS xv

LIST OF ABBREVATIONS xvi

LIST OF APPENDICES xvii

1 INTRODUCTION

1.1 Background of The Problem 1

1.2 Applications of automobile systems 3

1.2.1 Autonomous Vehicles Application 3

(7)

viii

1.2.3 Military Applications 4

1.2.4 A Safety Application 4

1.3 Range 4

1.4 Antenna Position 5

1.4.1 Front Bumper Area 5

1.4.2 Windscreen Area 6

1.5 Antenna Size 7

1.6 Objective Of The Project 8

1.7 Scope of The Project 8

1.8 Methodology Of The Project 8

1.9 Organization of Thesis 9

2 LITERATURE REVIEW

2.1 Introduction 10

2.2 Historical Development Of Microstrip Antennas 10

2.3 Frequency Allocated For Automobile Applications 11

2.4 Basic Microstrip Antenna 12

2.5 Advantages Vs. Disadvantages Of Microstrip Antennas 13

2.6 Applications Of Microstrip Antennas 16

2.7 Substrate Materials 17

2.8 Excitation Techniques 18

2.8.1 Microstrip Feed 19

2.8.2 Coaxial Feed 20

2.9 Methods Of Analysis 21

2.10 General rectangular patch design 21

2.11 Substrate selection 22

2.12 Substrate Comparison 23

2.13 Element Width and Length 24

2.14 Fringing effects 24

(8)

ix

2.16 Series Fed Arrays 25

2.17 Rectangular Patch Array Antenna Design 26

2.18 Wavelength 27

2.19 Characteristic Impedance 28

2.20 Element Width 30

2.21 Element Length 31

2.22 Quarter – wave transformer 32

2.23 Antenna properties 32

2.23.1 Input Impedance 33

2.23.2 VSWR 34

2.23.3 Bandwidth 35

2.23.4 Radiation pattern 35

2.23.5 Directivity 38

2.23.6 Gain 40

2.23.7 Polarization 41

2.23.8 Radiation efficiency 41

2.24 Mutual Coupling in Arrays 42

2.25 Chapter Summary 43

3 METHODOLOGY AND DESIGN SIMULATION

3.1 Introduction 44

3.2 Project methodology 44

3.3 Design Specification 46

3.3.1 Dielectric Substrate 48

3.3.2 Microstrip Feed Line Width 49

3.3.4 Single Patch Antenna specification 50

3.3.4.1 Wavelength 51

3.3.4.2 Guided Wavelength 51

3.3.5 Array Patch Specification 52

(9)

x

3.4 Single patch design 53

3.5 Array Patch Design 59

3.6 Analysis and Discussion 66

4 DESIGN FABRICATION AND MEASUREMENT RESULTS

4.1 Introduction 69

4.2 Fabrication method 69

4.3 Measurement Method 72

4.3.1 Return Loss Measurement Method 73

4.3.2 Radiation Pattern Measurement Method 74

4.3.3 Gain Measurement Method 75

4.4 Array Patch Design Fabrication Results 76

4.4.1 Return Loss 76

4.4.1.1 Data Measurement 76

4.4.1.2 Comparison of the results 77

4.4.2 Radiation Pattern 79

4.4.3 Gain 83

4.5 Analysis and discussion 85

5 CONCLUSION AND FUTURE WORK

5.1 Conclusion 87

(10)

xi

REFERENCES 90

BIOGRAPHIES 92

APPENDICES

APPENDIX A 93

APPENDIX B 94

APPENDIX C 96

APPENDIX D 98

APPENDIX E 99

APPENDIX F 101

APPENDIX G 103

APPENDIX H 105

APPENDIX I 109

(11)

xii

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Comparison between advantages and disadvantages of the

microstrip antennas 15

2.2 Substrate Comparison 23

3.1 dielectric substrate specifications 49

3.2 summary of patch characteristics 52

3.3 parametric optimization table of the array design simulation

results 61

3.4 summary of radiation pattern simulation results 67

4.1 a comparison of the radiation pattern results for simulation

and fabrication 82

4.2 a comparison between simulation and fabrication measured

(12)

xiii

LIST OF FIGURES

FIGURE NO. TITLE

_PAGE

2.1 Basic Configuration of Microstrip Antenna 13

2.2 Microstrip Line Fed Antennas 19

2.3 Coaxial Fed Microstrip Antennas 20

2.4 General design of rectangular patch antenna 22

2.5 Extremely wide (w >> h) and extremely narrow (w << h)

microstrip lines 25

2.6 Radiation lobes and beamwidths of an antenna pattern. 37

2.7 Linear plot of power pattern and its associated lobes and

beamwidths 38

3.1 Project methodology block diagram 45

3.2 proposed microstrip array antenna design 47

3.3 two dimensional view of a single patch 53

3.4 three dimensional view of a single patch 53

3.5 input impedance simulation result of a single patch design

54

3.6 Return loss simulation results of a single patch design 55

3.7 VSWR simulation result of a single patch design 56

3.8 E-plane Radiation Pattern simulation result of a single

patch design 57

3.9 H-plane Radiation Pattern simulation result of a single

patch design 58

3.10 two dimensional view of 4-element array patch design 59

(13)

xiv

3.12 parametric optimization graph of the array simulation results

60

3.13 Input Impedance simulation result of 4-element array

design 62

3.14 Return loss simulation results of 4-element array design 62

3.15 VSWR simulation result of 4-element array design 63

3.16 E-plane Radiation Pattern simulation result of the array

design 64

3.17 H-plane Radiation Pattern simulation result of the array

design 65

4.1 The FR4 Board Cutter 70

4.2 The UV Light Equipment 71

4.3 fabrication of the 4-element array 72

4.4 Macroni Instrument Scalar Analyzer 73

4.5 Return Loss Measurement Test Setup 73

4.6 the Anechoic Chamber used to measure the radiation

pattern 74

4.7 devices used to measure the gain 75

4.8 Return Loss fabrication results 76

4.8 comparison of Return Loss results of simulation and

fabrication 78

4.9 E-plane radiation pattern fabrication results 80

4.10 H-plane radiation pattern fabrication results 81

4.11 measured gain at angle 0 degree compared with

monopole standard gain 84

4.12 measured gain at angle 30 degree compared with

monopole standard gain 84

(14)

xv

LIST OF SYMBOLS

SYMBOL DISCRIPTION

E Electric Field Intensity

f Frequency

G Gain

H Magnetic field

I Current

J Current Density

K Wave number

U Radiation Intensity

Umax Maximum radiation intensity Z0 Characteristic impedance

ZL Load impedance

Zin Input impedance

C Coupling

D Directivity

h Substrate heigt

c Velocity of light in free space Ψ Progressive phase

λ wavelength

λg Guided wavelength

β Phase constant

εr Dielectric constant

εeff Effective dielectric constant

Φ Azimuth angle

θ Elevation angle

η Efficiency

Γ Reflection coefficient

μ Permeability

(15)

xvi

LIST OF ABBREVIATIONS

ABBREVIATION DISCRIPTION

RF Radio Frequency

ISM Industrial, Scientific and Medical

PCB Printed Circuit Board

EM Electromagnetic

UV Ultra Violet

VSWR Voltage Standing Wave Ratio

HPBW Half Power BeamWidth

(16)

xvii

LIST OF APPENDICES

APPENDEX TITLE

A Single patch design return loss simulation result 93

B Single patch design E-plane radiation pattern simulation

result 94

C Single patch design H-plane radiation pattern simulation

result 96

D Array patch design return loss simulation result 98

E array patch design E-plane radiation pattern simulation

result 99

F array patch design H-plane radiation pattern simulation

result 101

G Array patch design return loss fabrication measurement

result 103

H array patch design E-plane radiation pattern fabrication

measurement result 105

I array patch design H-plane radiation pattern fabrication

measurement result 109

(17)

CHAPTER 1

INTRODUCTION

1.1 Background of the problem

This thesis proposes the development of microstrip rectangular patch

antennas in array configuration that can be implemented for point-to-point

microwave link. In the first chapter, the background of this project has discussed,

providing the objective and scope of this work in addition to the application of

automobile radar antenna and the antenna position.

Communication can be broadly defined as the transfer of information from

one point to another. A communication system is usually required when the

information is to be conveyed over a distance. The transfer of information within the

communication system had commonly achieved by superimposing or modulating the

information into an electromagnetic wave, which acts as a carrier for the information

signal. At the required destination, the modulated carrier was then received and the

original information signal can be recovered by demodulation. Over the years,

(18)

2

carrier waves operating at radio frequencies as well as microwave and millimeter

wave frequencies. [1]

At frequencies below 3 GHz, many different types of antennas are used such

as simple monopole, dipoles, patches or arrays. Dish antennas are generally practical

and commonly used at microwave frequencies (above approximately 3 GHz). In

wireless data applications, satellite communications and other high bandwidth

microwave applications. [1]

Point to point communication brings a crucial responsibility to antennas since

they are expected to provide the wireless transmission between those devices, beside

being able to indicate good signal to noise ratio and immunity to noise, the antennas

in microwave links will have portray compact structures and ease of construction to

be mounted on various devices. [2]

In high performance pint to point application where size, weight, cost,

performance and ease of installation are very much required. To meet these

requirements, microstrip antennas are preferred; they are currently one of the fastest

growing segments in the telecommunications industry and promise to become the

preferred medium of telecommunications in the future. Since early days, there has

been tremendous worldwide activity aimed to develop an efficient antenna. [1]

Although microstrip antenna has several advantages like low profile, light

weight and simple to manufacture, it also has several disadvantages like low gain,

narrow bandwidth with associated efficiency is low. These disadvantages can;

however be overcome with intelligent designs incorporated in whole antenna

structures. One of the ways to overcome these problems is by constructing many

patch antennas in array configuration. [1]

For this project, microstrip patch array antenna was designed, simulated, and

fabricated for point-to-point communication. Results between simulation and

(19)

3

1.2 Applications of automobile systems

Millimeter wave radars are used as forward looking sensors in order to detect

and discriminate cars and obstacles on the road far ahead. On the other hand, it is

also used for measurement of speed over ground, road surface condition sensing

(rain, ice), detection of near-by ear and side obstacles, as well as detection of road

boundaries and early warning of side crash impact. Many types of automobile radar

system applications will be discussed as follows: [3]

1.2.1 Autonomous Vehicles Application

The car radar has a possible use in autonomous vehicles, where the range fills

the gap between the "navigation" sensors (as GPS) and the short-range "parking"

sensors. Possible applications include vehicles running in fairly standardized paths,

as mining trucks, cleaning vehicles and also some agricultural vehicles. [3]

1.2.2 Surveillance From A Fixed Spot Application

Another application of these methods is to detect for example cars breaking

down in sensitive road areas, as bridges, where a stopped car would rapidly lead to

traffic congestion. [3]

Tracking of moving targets, i.e. of objects in the dynamic picture, can be used

for example as surveillance of traffic flow. The radar can determine the instantaneous

average speed in different lanes, warn for congestion and for traffic stops, and

(20)

4

Also, target tracking makes it possible to log the number of vehicles passing

an area defined by "tripwires" and give accurate information on these vehicles

(passing time, velocity, which way they leave the surveyed area etc.). [3]

1.2.3 Military Applications

The car radar in itself is short-range surveillance radar, useful for short range

border surveillance and for guard (sentinel) duties, also in total darkness to use the

same radar sensor as a driving aid and as an aid to guard and surveillance duties.

When the vehicle is parked, the car radar is switched to "guard mode", and the

vehicle guards itself! The car radar can be the soldier's "Personal Radar". [3]

1.2.4 A Safety Application

Obstacles on the track, and people deliberately or inadvertently intruding on

the rail area, are great safety problems for the subway and other urban rail public

transport an intrusion alarm able to detect people is required. [3]

1.3 Range

Over the years but in most cases the basic intention has been to provide

measurement of range, velocity and angle of targets on the highway to enable

longitudinal control of the radar equipped vehicle to be undertaken. To achieve this

the radar has to operate in an environment ranging from scorching heat to

(21)

5

consistent performance at low cost These are severe constraints for a radar system

[3].

Road surface sensing is performed at close range and thus allows wide beam,

simple and small antennas. A variant in between is required for side and forward

looking (imaging) radar allowing crash prediction with range requirements on the

order of a few meters; however, while sensors with simple and small antennas may

suffice here, the angular discrimination of near-by objects requires a distribution of

sensors with many wavelengths spacing.[3]

Vehicle radar can be used for anti – collision and cruise control purposes to

measure the relative speed and distance between adjacent vehicles in the same lane, a

range of up to 200 meters is required. [3]

1.4 Antenna Position

To date, two basic positions have been used for the placement of the sensor.

Each of these has its merits and demerits. [3]

1.4.1 Front Bumper Area

The front bumper area is an apposition which may include the front grille.

This position provides many advantages and disadvantages as discussed below:

 Advantages:

(22)

6

 Disadvantages:

 It may be subject to impact during an accident or even during parking. Even

if no operational damage is sustained any impact damage may cause

misalignment of the sensor.

 The low mounting height exacerbates the multi-path problem and the sensor

aperture is likely to be contaminated by road dirt that will require mechanical

cleaning.

 Being external it is to be expected that in winter the aperture can become

covered with ice that may severely degrade the sensor performance.

 Heating the aperture to overcome this problem may not be that simple since

conductive wires buried in the aperture may affect the radar beam.

 If the license plate is considered for use as a Radom then the legislative

requirements of some countries may preclude this use if metallization of the

plate is required.

 The space available in the front bumper/grille area may be inadequate for

housing the sensor.[3]

1.4.2 Windscreen Area

The position considered here is - the area generally occupied by the rear view

mirror. This has a number of advantages, and disadvantages.

 Advantages:

 The sensor is inside the vehicle in a position that is mechanically cleaned by

the windscreen wipers.

(23)

7

 Disadvantages:

 The effect of the removal of backscatter from the wiper which should have to

be considered.

 The effect of heating elements in the windscreen has also been questioned.

 Loss measurements at 76 GHz on a heated windscreen have shown an

average loss due to attenuation and scattering of 9 dB, with a variation of 1.6

dB as the windscreen was rotated through 90°. This will induce a significant

reduction in radar performance.

 The space available in the area of the rear view mirror is severely limited and

will constrain the size and type of antenna structure.

 With direct solar radiation through the windscreen this area of the vehicle

may reach very high temperatures in hot climates.

 Depending on the design of the front of the vehicle this mounting position

may well induce blind ranges, at close range, due to the bonnet of the vehicle

screening the radar beam.

 It is probable that by raising the sensor up to the maximum height possible in

the vehicle, so that the effects of multi-path will be reduced. [3]

1.5 Antenna Size

The size of the antenna is a direct function of the radar operating frequency,

the higher the frequency the smaller the antenna for the same beam width. At 10

GHz the formation of a 3" wide beam requires an antenna with an aperture of

approximately 600". At 77 GHz a 3" wide beam requires an antenna with an aperture

of only 80 mm, so that, the antenna is a cost critical component of an automotive

(24)

8

1.6 Objective Of The Project

The aim of this project is to design, simulate, and fabricate a microstrip patch

array antenna operating in ISM Band at 2.45 GHz, pint to point communication for

automotive radar system.

1.7 Scope of The Project

The project is divided into few phases as follows:

 Understanding the fundamentals of microstrip rectangular patch antenna  Design a Microstrip rectangular patch array antenna.

 Simulate the Microstrip rectangular patch array antenna using microwave

office 2004, v 6.51.  Fabricate the design.

 Analyze and compare between fabrication and simulation results.

1.8 Methodology Of The Project

To carry out this project, the following methodology is designed:

 Generating the model, starting with a rectangular patch and then complete the whole antenna array model

(25)

9

 Testing and verification.

The following figure is a block diagram of the project methodology which

describes the methods will be used in implementing this project.

1.9 Organization of Thesis

The layout of this thesis has organized in five chapters. The first chapter is an

introduction, which provides information regarding the project background,

objectives, scope of the project and layout of the thesis.

The literature review that discussed in the second chapter will presents the

application and a background to the project that includes a microstrip antenna

overview, single rectangular patch antenna design followed by rectangular patch

array antenna design, basic antenna theory in addition to the array antenna theory and

its properties.

The third chapter shows the methodology of the thesis besides explaining the

software needed for the project and the methods that employed. Design and

simulation results has shown by presenting all the design specifications and results

obtained from MathCAD calculation followed by simulation results using AWR

MICROWAVE OFFICE 2004, v.6.51, and subsequent analysis that discussed.

Fabrication method, results, and analysis of fabrication and comparison

between simulation and fabrication results were explained in chapter 4, which are

Design Fabrication and Measurement Results.

The last chapter is a Conclusion and Future Work. This chapter will conclude