final thesis report1rrsg.uct.ac.za/members/greg/download/thesis_greg_chen.pdf · this thesis was...

Printed Circuit Board Dipole Antennas and Dipole Antenna Array Operating at 1.8GHz

i

Declaration

I declare that this thesis is my own unaided work, and hereby certify that unless stated,

all work contained within this paper is my own to the best of my knowledge.

This thesis is being submitted for the degree of Bachelor of Science in Engineering

(Electrical Engineering) at the University of Cape Town.

Tai-Lin Chen 13 October 2003


ii

Acknowledgements

I would like to thank my supervisor, Professor B J. Downing for his guidance and

expertise throughout this thesis.

I am grateful to the following people for their helpful advices and assistance:

• Professor M. Reineck for the advices that he has given me, especially on

testing the antennas.

• Mr. P. Daniels for his advices on etching the printed circuit board antennas.

• Mr. M. Lennon for demonstrating to me on how to crimp BNC cables.

• My colleagues for their assistance in gathering information needed for this

thesis.


iii

Terms of Reference

This thesis was commissioned by Professor B J. Downing on the 14th of July 2003 in

particular fulfillment of the degree in Electrical Engineering at the University of Cape

Town.

Professor Downing’s specific instructions were:

1. To investigate and understand the basic principles and concepts involved in

designing antennas and antenna arrays.

2. To determine the most suitable antenna for 1.8GHz commercial applications.

3. To design and fabricate the antennas and antenna array.

4. To test and analyze the antennas and antenna array built.

5. To draw conclusions based on the findings.

6. To make appropriate recommendations for improvements and future research.

7. To submit the thesis by 21st October 2003.


iv

Synopsis

The two most widely used frequencies for radio communications around the world in

recent years are the 900MHz and the 1.8GHz bands due to the global rise in the

industry of cellular networks. Most wireless communication devices manufactured

today are using monopole antennas owing to it simple structure, omnidirectivity and

its small size. However, these factors limit its signal strength because of the low gain.

This is particularly apparent in the 1.8GHz band. A solution for this problem lies

within the printed circuit technology, for its compact and cost effective nature.

This thesis involved determining the most suitable printed circuit board antenna to

use, designing it, implementing a suitable antenna array and testing it for the purpose

of 1.8GHz wireless application.

The design project will include understanding the principle theories and properties of

antenna, microstrip, balun (balanced to unbalanced transformer) and antenna array.

These important factors were acknowledged and understood before design procedures

took place.

After studying different types of antennas, designing of PCB dipole antennas were

proposed due to its appropriate nature, these being omnidirectional, compact and cost


v

effective. As a dipole antenna needs a balun to be compatible for connection to a

co-axial cable, hence balun designs were also proposed.

An important objective of this thesis was to provide a solution to the setback of

having low antenna gain in mobile wireless devices. The proposed solution is to

design a suitable antenna array to increase antenna gain, and at the same time

retaining the omnidirectivity desired. A four elements corporate fed array was then

chosen as the array design, as its simple configuration meant that omnidirectivity and

manipulation of the arrays were possible if further testing were to be conducted for

optimum antenna performance.

The design procedure includes the following:

• Building of prototype antennas to assists in familiarizing with fabrication

techniques, and eliminating erroneous designs.

• Design and fabrication of etched PCB dipole antennas.

• Design and fabrication of etched antenna array components

Tests and analysis was carried out on etched products after it was fabricated. The tests

conducted include Impedance matching of all components, and the power radiation of

the antenna array and the array element employed.

Conclusions were drawn from the test results, indicating that the antenna array built is

satisfactory and have achieved the objective set for this thesis, which is to design and

build a high gain omnidirectional printed circuit board dipole antenna array operating

at 1.8GHz. Recommendations are then made on the improvements, future testing


vi

methods and possible application of the antenna array. Further research and testing on

the current antenna array has also been proposed.


vii

Contents

DECLARATION ....................................................................................................................................I

ACKNOWLEDGEMENTS ................................................................................................................. II

TERMS OF REFERENCE.................................................................................................................III

SYNOPSIS ........................................................................................................................................... IV

CONTENTS....................................................................................................................................... VII

LIST OF FIGURES.............................................................................................................................XI

LIST OF TABLES ............................................................................................................................XIII

INTRODUCTION ................................................................................................................................. 1

1.1 BACKGROUND ............................................................................................................................... 1

1.1.1 Printed Circuit Board Antennas............................................................................................ 2

1.1.2 Antenna Array ....................................................................................................................... 2

1.2 OBJECTIVES................................................................................................................................... 3

1.3 LIMITATIONS OF RESEARCH ........................................................................................................... 3

1.4 SOURCE OF INFORMATION ............................................................................................................. 4

1.5 PLAN OF DEVELOPMENT................................................................................................................ 4

LITERATURE REVIEW ..................................................................................................................... 6


viii

2.1 ANTENNA PROPERTIES................................................................................................................... 6

2.1.1 Impedance ............................................................................................................................. 6

2.1.2 Wavelength ............................................................................................................................ 7

2.1.3 Gain ...................................................................................................................................... 7

2.1.4 Effective Area ........................................................................................................................ 8

2.1.5 Directivity.............................................................................................................................. 9

2.1.6 Efficiency............................................................................................................................. 10

2.1.7 Polarization......................................................................................................................... 10

2.2 PRINTED CIRCUIT BOARD ANTENNA ........................................................................................... 11

2.2.1 Types of Microstrip Antenna ............................................................................................... 12

2.2.2 Microstrip Line ................................................................................................................... 12

2.2.3 Discontinuity ....................................................................................................................... 14

2.3 BALUN......................................................................................................................................... 15

2.4 ANTENNA ARRAY......................................................................................................................... 16

2.4.1 Array Theory ....................................................................................................................... 16

2.4.2 Array Architecture............................................................................................................... 17

2.5 DESIGN CONSIDERATION ............................................................................................................. 18

PROPOSED DESIGN......................................................................................................................... 20

3.1 PROPOSED PCB DIPOLE RADIATOR DESIGN ................................................................................ 21

3.2 PROPOSED BALUN DESIGN .......................................................................................................... 22

3.3 PCB DIPOLE ANTENNA ............................................................................................................... 23

3.4 ARRAY DESIGN ............................................................................................................................ 23

DESIGN AND FABRICATION METHODS .................................................................................... 26

4.1 DESIGN PROCEDURES .................................................................................................................. 26

4.2 BUILDING AND TESTING OF PROTOTYPE MICROSTRIP ANTENNAS ............................................... 27


ix

4.2.1 Prototype Designs ............................................................................................................... 27

4.2.2 Prototype Performance ....................................................................................................... 29

4.3 DESIGNS OF PCB ANTENNAS ...................................................................................................... 31

4.4 ARRAY DESIGN ............................................................................................................................ 34

TESTS AND ANALYSIS OF PCB DIPOLE ANTENNAS AND ANTENNA ARRAY .................. 37

5.1 IMPEDANCE MATCHING OF ETCHED ANTENNAS .......................................................................... 37

5.1.1 |S11|2 Test on PCB Dipole Antennas ................................................................................... 38

5.1.2 Error Analysis ..................................................................................................................... 40

5.1.3 Frequency Correction on the 10mm Design........................................................................ 40

5.2 ANTENNA ARRAY TEST AND ANALYSIS........................................................................................ 41

5.2.1 Array Element Performance ............................................................................................... 42

5.2.2 Array Power Splitter ........................................................................................................... 44

5.2.3 Antenna Array Performance ............................................................................................... 45

CONCLUSIONS AND RECOMMENDATIONS ............................................................................. 48

6.1 CONCLUSIONS ............................................................................................................................. 48

6.1.1 Results of Array Elements ................................................................................................... 48

6.1.2 Results of Array Power Splitter........................................................................................... 49

6.1.3 Results of Antenna Array .................................................................................................... 49

6.2 RECOMMENDATIONS.................................................................................................................... 50

6.2.1 Improvements on the Antenna Array................................................................................... 50

6.2.2 Antenna Testing Recommendations..................................................................................... 51

6.2.3 Possible Antenna Array Application ................................................................................... 51

6.2.4 Proposed Further Testing.................................................................................................... 51

BIBLIOGRAPHY ............................................................................................................................... 53


x

APPENDIX A....................................................................................................................................... 54

APPENDIX B....................................................................................................................................... 56

APPENDIX C ...................................................................................................................................... 62


xi

List of Figures

Figure 2.1: Elliptically Polarized Electromagnetic Field............................ 11

Figure 2.2: Microstrip Line......................................................................... 12

Figure 2.2.3: Discontinuity Equivalent Circuit........................................... 15

Figure 2.4.1: Array...................................................................................... 17

Figure 2.4.2: Four Elements Corporate Fed Array ..................................... 18

Figure 3.1: Proposed Dipole Radiator Design ............................................ 21

Figure 3.2: Proposed Balun Designs........................................................... 22

Figure 3.3: Balun Designs........................................................................... 23

Figure 3.4: Proposed Array Design............................................................. 24

Figure 4.1.1: Prototype Design A ............................................................... 28

Figure 4.1.2: Prototype Design B ............................................................... 28

Figure 4.1.3: Balun to Ground Plane Width Ratio 3:1................................ 28

Figure 4.1.4: Prototype Design C ............................................................... 29

Figure 4.1.5: |S11|2 of Prototype Design A ................................................. 29

Figure 4.1.6: |S11|2 of Prototype Design B ................................................. 30

Figure 4.1.7: |S11|2 of Prototype Design C ................................................. 30

Figure 4.2.1: 8mm PCB Dipole .................................................................. 32

Figure 4.2.2: 10mm PCB Dipole ................................................................ 33


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Figure 4.2.3: 12mm PCB Dipole ................................................................ 33

Figure 4.2.4: Wideband PCB Dipole .......................................................... 33

Figure 4.3.1: Corporate Fed Array Power Splitter...................................... 34

Figure 5.1.5: 10mm PCB Dipole after Frequency Correction .................... 41

Figure5.2.2: Polar Radiation Test Configuration ........................................ 43

Figure 5.2.3: Polar Radiation of an Array element ..................................... 43

Figure 5.2.4: Impedance Terminator Connections...................................... 44

Figure 5.2.6: Antenna Array........................................................................ 45

Figure 5.2.7: |S11|2 of Antenna Array ......................................................... 46

Figure 5.2.8: Polar Radiation of Antenna Array ......................................... 46

Figure B1: Photograph of Prototype Design A |S11|2 Test Result .............. 57

Figure B2: Photograph of Prototype Design B |S11|2 Test Result .............. 57

Figure B3: Photograph of Prototype Design C |S11|2 Test Result .............. 58

Figure B4: Photograph of 8mm PCB Dipole |S11|2 Test Result ................. 58

Figure B5: Photograph of 10mm PCB Dipole |S11|2 Test Result ............... 59

Figure B6: Photograph of 12mm PCB Dipole |S11|2 Test Result ............... 59

Figure B7: Photograph of Wideband PCB Dipole |S11|2 Test Result ......... 60

Figure B8: Photograph of 1.8GHz PCB Dipole |S11|2 Test Result............. 60

Figure B9: Photograph of Array Power Splitter |S11|2 Test Result............. 61

Figure B10: Photograph of Antenna Array |S11|2 Test Result .................... 61


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List of Tables

Table 2.1: PCB Antenna Characteristics ..................................................... 12

Table 4.1: Prototype |S11|2 Analysis ........................................................... 31

Table 5.1: PCB |S11|2 Analysis ................................................................... 40


1

Chapter 1

Introduction

This thesis describes the design, construction and testing of printed circuit board

dipole antennas and dipole antenna array operating at 1.8GHz.

1.1 Background

In recent years the two most widely used frequencies for radio communications

around the world are the 900MHz and the 1.8GHz bands due to the global rise in the

industry of cellular networks. Yet as we progress through this rapidly growing market,

one important factor that has immense potential to improve is the signal strength of

the cellular devices that we carry. Most wireless communication devices that have

been marketed today are using monopole antennas due to it simple structure,

omnidirectivity and its small size. It is due to these factors that its signal strength is

limited by the low gain of these antennas, this is especially apparent in the 1.8GHz

band. [1]

As these commercial devices evolve, the demands for better performance will rise,


2

yet these products must still keep its limitations within the boundaries of being easy

to implement, cost effective and physically small. Hence the simple reflector antennas

that are widely used today may no longer suffice in the future. A solution for this

problem lies within the printed circuit technology, for its improved performance and

cost effective nature. This thesis involved determining the most suitable printed

circuit board antenna to use, designing it and testing it. [2, 3]

1.1.1 Printed Circuit Board Antennas

PCB antennas dates back to the early 1950’s, but due to the lack of good low cost

microwave substrates the developments of these antennas were limited over the next

15 years. A rapid development in PCB antennas started in the 1970’s as thin, low cost

antennas were needed for missiles and spacecrafts.

PCB or microstrip antennas are an extension of the microstrip transmission line.

A basic microstrip structure contains a thin substrate between 2 metal sheets which

are usually copper. Microstrip line is then formed by etching away the necessary

metal on top surface in so forming a strip. As long as the physical dimension of the

strip and the relative dielectric constant remains unchanged, virtually no radiation will

occur. By shaping the microstrip line into a discontinuity, power will radiate off from

an abrupt end in the strip line. [2]

1.1.2 Antenna Array

A single antenna element is often limited to many applications because of its low gain

and wide beam width. Where a higher gain, narrower beam width and increased range


3

are required, an array of antenna is to be implemented. In a physical terms, an antenna

array would be multiple elements of antennas, in a linked configuration placed equal

distances apart to achieve the desired higher gain.

1.2 Objectives

The objectives of this thesis are:

• To determine the best suited PCB antenna for cellular devices.

• To propose a design and fabricate the chosen PCB antenna.

• To test and analyze the suitability of this antenna using the network

analyzer and the power meter, thus measuring the impedance matching and

the power radiated at 1.8GHz respectively.

• To design and fabricate an appropriate antenna array configuration for the

antenna.

• To test and analyze the suitability of the antenna array by using the network

analyzer and the power meter.

• To draw conclusions and make recommendations on how the PCB antenna

built can be improved over the present design for the suitability of wireless

communication devices at 1.8GHz.

1.3 Limitations of Research

As an anechoic chamber was not available, measurements such as antenna gain,

polarization, directivity and back radiations are effected by external objects and finite

ground planes which cause reflection producing irregularities in radiation patterns.


4

This limits the accuracy of antenna measurement greatly.

Far-field pattern measurements are not considered highly accurate in this thesis as

antennas would need to be taken to a reflection free far-field testing range located in

Gauteng, which is not available at UCT.

1.4 Source of Information

The information and knowledge on which this report was based upon was acquired

from Prof. B Downing, sites from the internet, Documents from the University of

Cape Town as well as test and analysis that are conducted on the built antennas.

1.5 Plan of Development

The report covers the following sections in the following order:

• Principles and concept involved in determining and constructing of a

suitable PCB antenna.

• Proposed designs of the chosen antenna.

• Methods used in design and fabrication of antennas and antenna array.

• Test performed and error analysis on the built antennas and antenna array.

• Make conclusions and recommendation on the suitability of the antenna

array and suggestions of improvements.


5

References

[1] Sainati, Robert A. CAD of Microstrip Antennas for Wireless Applications.

London: Artech House, Inc, 1996, pp. 1.

[2] Chang, Kai. RF and Microwave Wireless Devices. Texas A&M University: John

Wiley & Sons, Inc, 2000, pp. 1-3

[3] Professor B J. Downing


6

Chapter 2

Literature Review

This chapter goes through the theories and properties of antenna, microstrip, balun

and antenna array. These important factors were needed to be acknowledged,

understood and practiced for this thesis.

2.1 Antenna Properties

This section describes the important properties of antennas, all of which crucial when

determining and designing antennas for applications. Since this is a practical project,

there was no attempt to present more fundamental antenna theory.

2.1.1 Impedance

The characteristic impedance of the transmission line that is connected to the antenna must equal input impedance of the antenna. Antenna resistance is also called radiation resistance. This factor is defined as the resistance that would dissipate as much power as the transmission line for which it is connected to. Antenna resistance is defined [1]:


7

2IPR = (2.1)

Where R is the antenna resistance

P is the power dissipated

I is the current drawn from the antenna

2.1.2 Wavelength

The frequency at which the antenna operates at is dependant upon its wavelength. The

following equation describes this relationship [1]:

fc

=λ (2.2)

Where λ is the wavelength

c is the speed of light ( 8103× m/s)

f is the operating frequency of the antenna

2.1.3 Gain

This antenna property is used to compare differences in antenna radiation

characteristics, both directivity and efficiency needs to be taken into account when

determining antenna gain. This comparison is done by using a reference antenna of

known gain, generally either a monopole antenna or a dipole antenna. Therefore when

we talk about a gain of an antenna, it is meant the gain for which the antenna

improves beyond the reference antenna. The gain of an antenna can be expressed as a


8

power ratio [2]:

( )

=

1

210log10

PPdBA (2.3)

Where A is the gain

P2 is the power of the reference antenna

P1 is the power of the actual antenna

The power received by an antenna through free space can be expressed as:

22

2

16 dGGPP rtt

r πλ

= (2.4)

Where Pr is the power received

Pt is the power transmitted

Gt is the transmitting antenna gain

Gr is the receiving antenna gain

λ is the Wavelength in meters

d is the distance between the antennas, in metres

2.1.4 Effective Area

Effective area of an antenna can be said to be the measure of the effective

transmitting or receiving area presented by an antenna. It is normally proportional,

but less than, the physical area of the antenna. Effective are can be expressed as a

relationship to gain by [1]:


9

πλ4

2

GAe = (2.5)

Where Ae is the effective area

G is the gain of the antenna

λ is the wavelength in meters

2.1.5 Directivity

Directivity is the term used when measuring how focused an antenna radiation pattern

is. Directivity can be divided into two classes, Omni-directional and directional.

Omni-directional antennas radiate and receive signals from all directions at the same

time with the trade off of having a limited gain. Where directional antennas radiate

and receive signals at a beam width that directed outwards from the antenna, either at

one or opposite directions with a higher gain than omni-directional antennas.

For any antenna, the directivity can be related to its effective area [2]:

2

24λπ eA

D = (2.6)

Where D is the directivity, and

Ae is the effective area

λ is the wavelength in meters

For small Beam width radiation, directivity can be also approximated by [3]:


10

verticalhorizontal

D5.05.0

27000αα

= (2.7)

Where α0.5horizontal is the horizontal half-power beamwidth

α0.5vertical is the vertical half-power beamwidth

2.1.6 Efficiency

This property is a measure of how much electrical power supplied to an antenna is

transformed into electromagnet and due to losses (imperfect dielectrics, eddy current

etc), not all energy transmitted to the antenna is radiated, with this the antenna

efficiency is defined as [2]:

lr

r

input

dtransmitte

RRR

PP

+==η (2.8)

Where η is the antenna efficiency

Ptransmitted is the transmitted power

Pinput is the input power

Rr is the antenna resistance

Rl is the resistance due to losses

2.1.7 Polarization

The electromagnetic wave that is radiated from an antenna is comprised of electric

and magnetic field. These fields are orthogonal to each other and to the direction of

propagation. The polarization of an antenna is described by the electric field

propagated. In general, all electromagnetic fields are elliptically polarized as shown


11

from the figure below [2, 4]:

Figure 2.1: Elliptically Polarized Electromagnetic Field

Where Ex is the electric field in the x-direction

Ey is the electric field in the y-direction

E is the total electric field, sum of Ex and Ey.

2.2 Printed Circuit Board Antenna

As mentioned before, PCB antennas are relatively simple structures where primary

complicating factor are the relations between microstrip lines, dielectric substrates

and the conducting ground plane. Although best accuracy can be achieved through

rigorous mathematical and computational approaches, for this thesis, simpler and

most widely used engineering methods were used. This section will describe all the

microstrip technology and techniques applied [5].


12

2.2.1 Types of Microstrip Antenna

Three main types of PCB antennas were considered. Mainly the patch, dipole, and

meander line antenna (MLA), the following table shows the characteristics of these

antennas at 1.8GHz [5]:

PCB Antennas Efficiency Directivity Physical Dimensions

Patch High Directional Compact

Dipole Medium Omnidirectional Compact

Meander line Medium Directional Large

Table 2.1: PCB Antenna Characteristics

2.2.2 Microstrip Line

The following figure shows the physical properties of a microstrip line:

Figure 2.2: Microstrip Line

The electric field lines are perpendicular to the microstrip line to the ground plane.


13

Most of the lines are concentrated below the strip where some lines partially extend

into the air space above. These lines are parallel to the conducting surfaces of the

microstrip lines. The magnetic field circles the microstrip line and doing so also

extends into the air space above the strip. Both fields that exist in the air space above

the strip reduce the effective dielectric constant seen by waves propagating along the

line. If the fields above the strip did not exist, then the dielectric constant would the

same as the substrate. The width and height of the microstrip line controls how much

the dielectric constant depends on the substrate, this in term affects crucial microstrip

parameters such as characteristics impedance and phase velocity, making them

frequency dependent. These factors provides us with analysis techniques in

calculating and designing microstrip lines, and hence PCB antennas.

The following synthesis formula helps approximate the width of microstrip lines [6]:

( )129.119+

=r

Aε

(2.9)

+

+−

=rr

rBε

ππεε

4ln

2ln

11

21 (2.10)

+

+= 244ln

2

hwhC (2.11)

r

Dε

π95.59= (2.12)

A, B, C, D parameter defined for convenience in applying the design formula


14

( )BCAZ −=0 (2.13)

−+

−

−+

−−−=

rr

r

ZD

ZD

ZD

hw

επ

πεεππ

π517.0293.01ln112ln12

000

(2.14)

Where w is the desired width of the microstrip line

h is the height of the microstrip line above the ground plane

Z0 is the characteristic impedance

εr is the relative dielectric constant

Due to difference in impedance with changing line width, impedance matching is

between two different impedance elements is necessary. This can be done by placing

a matching strip between the elements to be matched. The impedance of this

matching strip can be expressed by:

210 ZZZ = (2.15)

Where Z0 is the matched impedance

2.2.3 Discontinuity

Discontinuity is a term for a geometric change in the microstrip line referring to a gap,

notch or a bend in the strip. This physical change alters the electric and magnetic field

distributions of the strip resulting in energy storage and often radiation at the

discontinuity. Due to these factors showing similar characteristics as elements such as

capacitors and inductors, discontinuities can be expressed as the following equivalent

circuits:


15

Figure 2.2.3: Discontinuity Equivalent Circuit

2.3 Balun

The word balun is a contraction for “balanced to unbalanced”, where balanced means

that both terminals of the feed must be of the same voltage level with respect to

ground, if not then it is said to be unbalanced. This device is designed for systems

where a centre-fed antenna (dipole for example) which is a balanced device, is fed to

a coaxial line, which is unbalanced. The balance of the system is then upset as one

side of the antenna is connected to the outer shield while the other is connected to the

inner conductor. On the side connected to the shield, a current can flow across over

the outer of the coaxial line. The fields that exist outside cannot be cancelled by the


16

fields from the inner conductor as the fields within can not escape, and hence the

current flowing outside of the coaxial line will cause unwanted radiation. This is

called line radiation. Baluns manipulate the voltages at the antenna terminals equal in

amplitude with respect ground but opposite in phase, these voltages causes equal

amount of current to flow on the outside of the coaxial line. Since the current are

equal and out of phase with each other, they cancel out and hence reducing the effect

of line current [7].

2.4 Antenna Array

In some antenna applications, higher gain and narrower beam width is required to

increase range and to reject interference. Antennas can be arrayed to produce these

characters. In this section, array theory and architecture is discussed.

2.4.1 Array Theory

For derivation purposes, consider two identical antennas positioned on the x-axis in

figure 2.4. The antennas are separated by a distance d. If the two antennas were in

phase and applied with equal amplitude, Maxwell’s equation states that the total field

radiated by the antennas at distant points r (as distance at both distant points equal,

denoting both distance vector r) is given by the sum of the fields from each antenna.

Total field is expressed below [8]:

( ) ( ) ( )r

eEr

eEEjkrjkr −−

+= θθθ 21 (2.16)

Where E1 and E2 are fields radiated by the antennas


17

As the phase changes by 2π for every wavelength difference, the typical path length

differences of the antennas are on order of a half-wavelength can be approximated by:

( )θsin' dd ≈ (2.17)

The total field becomes:

( ) ( ) ( )[ ]θθθ sin1 1 jkd

jkr

er

eEE +=−

(2.18)

Figure 2.4.1: Array

2.4.2 Array Architecture

The simplest and easiest antenna array feed network to implement and design is the

corporate fed array. With this type of configuration, all the elements in the array are

connected in parallel linked by parallel power splitters. The amplitude levels of the

antenna elements are controlled by way the power splitters are configured.

The following figure shown is a typical four elements corporate fed array:


18

Figure 2.4.2: Four Elements Corporate Fed Array

2.5 Design Consideration

As my aim in this thesis is to determine and design a suitable antenna for the mobile

cellular technology, the following important factors are considered:

• Antenna designed needs to be omnidirectional for effective reception on

a mobile device.

• Array design and configuration needs to have the potential for simple

implementation and installation.

• The antenna needs to be compact in physical dimension for compatibility

in the mobile cellular industry.

• Cost effectiveness of the final product should be considered.

Power splitters


19

Reference

[1] Antenna Terminology, 5 August 2003.

http://www.skycross.com/terminology.asp

[2] Antenna Definition, 5 August 2003.

http://www.cs.mdx.ac.uk/ccm/ccm2012/Antenna.pdf

[3] Prof. M. Reineck, university of Cape Town. Lecture notes from course EEE497C,

RF Components and Satellite Systems.

[4] Antenna Polarization, 12 August 2003.

http://www.cushcraft.com/comm/support/pdf/Antenna-Polarization-14B32.pdf

[5] Chang, Kai. RF and Microwave Wireless Devices. Texas A&M University: John

Wiley & Sons, Inc, 2000, pp. 74-98

[6] Roddy, D. Microwave Technology. New Jersey: Prentice Hall, Inc, 1986, pp.

148-150

[7] Dean Straw, R. The ARRL Antenna Book. Newington: The American Radio

Relay League, 1994, Chapter 25-14.


London: Artech House, Inc, 1996, pp. 177-193.


20

Chapter 3

Proposed Design

As the antenna design needed to perform the requirements of the design consideration

mentioned in the last chapter, I chose to design PCB dipole antennas due to its

appropriate characteristics, these been omnidirectional, compact, cost effective.

Mentioned in the last chapter, a dipole antenna need a balun to be compatible for

connection to a co-axial cable, hence balun designs were also proposed.

A Corporate fed array was chosen for my array design, as its simple configuration

meant that manipulation of the arrays were possible if further testing were to be

conducted for optimum antenna design.


21

3.1 Proposed PCB Dipole Radiator Design

The following radiator design was proposed:

Figure 3.1: Proposed Dipole Radiator Design

This half-wave PCB dipole design, as to all half-wave dipole, has two

quarter-wavelength radiating elements. The radiating elements are connected to a

ground patch by two quarter-wavelength strips, these strips provide the ground plane

for the balun element on the other side of the substrate.

This radiator design is the “ground sheet” of the whole dipole antenna, where it is

connected to the ground/outer conductors of the co-axial cable. The copper sheet on

the other side of the substrate will be the balun, where it is connected to the feed/inner

conductor of the coaxial cable. These two sheets including the substrate in the middle

will form the whole PCB dipole antenna design. [2]

¼ λPosition x


22

3.2 Proposed Balun Design

There are two balun designs implemented. One is the short circuit design and the

other is the physically connected design. The following illustration shows the two

designs:

Figure 3.2: Proposed Balun Designs

In design “a”, the quarter-wavelength strips leading to the ground patch on the

radiating sheet mentioned in 3.1 acts as a ground plane for the balun microstrip line.

This microstrip line effectively has a gap in the ground plane between the two

radiating element, this gap is terminated by an open circuit a quarter wavelength away

at positioin y. The combination of these elements provides the balanced to unbalanced

transition and the necessary impedance needed [2].

In design “b”, position z is physically connected to position x. This design is

fundamentally similar to design “a”, except in this case it does not need to provide an

open circuit quarter-wavelength away to terminate the gap, it is already physically

b) Physically connected a) Short circuit

¼ λ

¼ λ

¼ λ

¼ λ

Position y

Position z Chamfered

bends


23

terminated [3].

The 45o diagonal chamfered (or metered) bends on the microstrip lines shown in the

figure above greatly minimizes the discontinuity reactance that would normally occur

on a bend, as these chamfered bend are electrically shorter than the physical distance

of the bend path. In an even more understanding perspective, a chamfered bend seems

though if it is guiding the signal travelling through the path [1].

3.3 PCB Dipole Antenna

The figure below explains illustratively how the previously mentioned designs in this

chapter are associated:

Figure 3.3: Balun Designs

3.4 Array Design

Considering that compactness in physical size is of importance, hence a suitable four

Physical connection between two sheets

Design “a” Design “b”


24

elements array was proposed. As in all corporate arrays, the antenna elements are

connected in parallel with linked parallel power splitters, hence the matching of

parallel impedance additions and antenna impedances are considered. The distances

between each element are, as supervised, is to be half a wavelength apart. Further test

can be conducted by altering the distance between array elements for optimum

antenna performance.

The design below illustrates how the impedance matching, array distances and

chamfered bends are accounted for:

Figure 3.4: Proposed Array Design

Impedance matching

Strips

Chamfered

bends

Antenna

Elements

λ/2 λ/2


25

References


London: Artech House, Inc, 1996, pp. 148-150.

[2] SPAS Hard Ware Design Antenna Array, 21 July 2003

http://www.enel.ucalgary.ca/People/Okoniewski/ENEL619-50/Projects2003/SPA

S/antenna.html

[3] 2.4GHz Diversity Polarization Diversity Antenna, 13 August 2003

http://www.swissatv.ch/documents/2.4GHz_diversity_polarization_diversity_dipole_antenna.pdf


26

Chapter 4

Design and Fabrication Methods

This chapter describes the design procedures taken in assisting linking knowledge

between the theoretical understandings, and the practical fabrication of antennas.

4.1 Design Procedures

The following design procedures were implemented, taking into consideration the

time and cost constraints:

• Design and building of prototype microstrip dipole antennas.

• Analyzing the performance of prototype antennas in helping designing the

etched PCB dipole antennas.

• Design and fabrication of PCB dipole antennas.

• Design and fabrication of antenna array panel.


27

4.2 Building and Testing of Prototype Microstrip Antennas

The reason for building these initial antennas are so that the relationship between

antenna theory and practical antenna building could be more understood before going

ahead in designing the final PCB antennas. Further, it is possible to “tune” these

antennas by trimming the copper strip conductors and adjusting the dimensions.

Three prototype antennas were built using different dimensions and methods, this

assists in determining which type would be more feasible for further design. All three

antennas were fabricated using 0.5mm copper plate as conductive sheet and 6mm

polypropylene substrate.

4.2.1 Prototype Designs

The width the microstrip lines used in these antennas are calculated using the

microstrip line synthesis equation (4.16), with the following known dimensions:

Operating Frequency: 1.8GHz

Substrate relative permittivity: 1.42

Height: 6mm

Impedance a) 61Ω

b) 75Ω

Calculated width = a) 15.08mm

b) 20.6mm

The length of the dipole antennas are λ/2, which is 83mm. This is split into two

radiating elements λ/4 in length (41.5mm), separated by a 5mm gap.


28

Design A:

Figure 4.1.1: Prototype Design A

In design A, balun width is equal to the width of its ground plane, forming a 1:1 ratio

between balun to ground [2].

Design B:

Figure 4.1.2: Prototype Design B

This design used a balun to ground plane width ratio of 3:1 as advised in the microstrip CAD, it is said that dipole antenna of such design need to implement this ratio to operate properly [1, pp 101-103].

Figure 4.1.3: Balun to Ground Plane Width Ratio 3:1

Design C:

Ratio 3:1

75Ω

61Ω

75Ω

61Ω


29

Figure 4.1.4: Prototype Design C

This design implemented the physically connected balun, using balun to ground plane

width ratio of 1:1 [3].

4.2.2 Prototype Performance

The antenna performances below were taken from the 211S readings on the

network analyzer.

Design A

-40-35-30

-25-20

-15-10-5

01500 1600 1700 1800 1900 2000 2100

MHz

dB

Figure 4.1.5: |S11|2 of Prototype Design A

61Ω

75Ω


30

Figure 4.1.6: |S11|2 of Prototype Design B

Design C

-25

-20

-15

-10

-5

01800 1900 2000 2100 2200 2300 2400

MHz

dB

Figure 4.1.7: |S11|2 of Prototype Design C

Design B

-20

-15

-10

-5

0

1000 1100 1200 1300 1400 1500 1600

MHz

dB


31

Prototype Centre Frequency

Operating Band Minimum Power Reflected

Maximum Power Reflected

Design A 1719 MHz 1649 – 1855 MHz 20 dB 40 dB

Design B 1280 MHz 1100 – 1500 MHz 15 dB 18 dB

Design C 2180 MHz 1840 – 2330 MHz 7 dB 22 dB

Table 4.1: Prototype |S11|2 Analysis

From the result shown above, we can see that neither the 1:3 balun to ground width

ratio nor the physically connected balun had the satisfactory result, hence the designs

for etched PCB antennas will be implemented using design A: Quarter-wavelength

short circuit balun with 1:1 balun to ground width ratio.

4.3 Designs of PCB Antennas

The designs of the PCB antennas in this section are developed from design A of the

prototype antennas, which proven to be the best balun configuration. At this stage, the

aim is to design the best suited antenna with respect to its bandwidth.

For a dipole antenna, the bandwidth is mainly dependent upon the width of the

radiating elements, hence four PCB dipole antennas with different dimensions (8mm,

10mm, 12mm, wideband) has been designed to understand this relationship further,

and from this, the best suited antenna were chosen for the array elements [4].


32

Microstrip line widths are calculated by using the synthesis equation (2.16)



Height: 1mm

Impedance a) 61Ω

b) 75Ω

Calculated width = a) 0.18mm

b) 0.8mm

The following antennas were drafted using AutoCad software, laser printed out in

scale 1:1 format and given to an etching service for it to be printed onto carbon films.

They then etched the designs onto printed circuit boards.

8mm Dipole:

Figure 4.2.1: 8mm PCB Dipole

8mm

75Ω

61Ω


33

10mm Dipole:


12mm Dipole:


Wideband Dipole:

Figure 4.2.4: Wideband PCB Dipole

10mm

12mm

Wideband

75Ω

75Ω

61Ω

61Ω

61Ω

75Ω


34

4.4 Array Design

As mentioned in the last chapter, the impedance matching and distances between

elements and power splitters are of crucial importance. By using the microstrip line

synthesis equation, the following widths are calculated:



Height: 1mm

Impedance a) 50Ω

b) 100Ω

c) 70.1Ω (matching of 50Ω to 100Ω)

Calculated width = a) 2mm

b) 0.4mm

c) 0.9mm

Figure 4.3.1: Corporate Fed Array Power Splitter

70.1Ω 50Ω

100Ω

X X

X


35

At points X, the two parallel 100Ω line joins giving an effective impedance of 50Ω.

These points are then matched to other 100Ω’s, resulting the 50Ω needed at the feed

point of the array. The lengths of the parallel 100Ω lines are all equal to provide

equivalent phase to all signals passing through. As mentioned previously, the shown

chamfered bends and joints have been implemented to minimize discontinuity

reactance [1].

The array power splitter was also drafted in AutoCad software and fabricated the

same way as the PCB antennas.


36

References


London: Artech House, Inc, 1996, pp 28.

[2] SPAS Hard Ware Design Antenna Array, 21 July 2003

http://www.enel.ucalgary.ca/People/Okoniewski/ENEL619-50/Projects2003/SPA

S/antenna.html

[3] 2.4GHz Diversity Polarization Diversity Antenna, 13 August 2003

http://www.swissatv.ch/documents/2.4GHz_diversity_polarization_diversity_dip

ole_antenna.pdf

[4] Prof. M. Reineck, university of Cape Town. Lecture notes from course EEE497C, RF Components and Satellite Systems.


37

Chapter 5

Tests and Analysis of PCB Dipole Antennas and

Antenna Array

Tests and analysis was carried out on the etched antennas and antenna array after it

was fabricated. The tests conducted include Impedance matching of all etched

products, and the power radiation of the antenna array and the antenna employed.

5.1 Impedance Matching of Etched Antennas

The |S11|2 reading shown on the network analyzer determines how well the

impedance is matched on the component that it is connected to. The test is an

indicator of the reflected power which analyzes whether the component is radiating at

the correct frequency, and its radiating bandwidth.


38

5.1.1 |S11|2 Test on PCB Dipole Antennas

The |S11|2 test was conducted on the following antennas:

8mm Dipole:

|S11|2 of 8mm Dipole

-25

-20

-15

-10

-5

0

1100 1200 1300 1400 1500 1600 1700

MHz

dB

Figure 5.1.1: |S11|2 of 8mm PCB Dipole

10mm Dipole:

|S11|2 of 10mm Dipole

-80

-60

-40

-20

0

1100 1200 1300 1400 1500 1600 1700

MHz

dB



39

12mm Dipole:

|S11|2 of 12mm PCB Dipole

-20

-15

-10

-5

0

1100 1200 1300 1400 1500 1600 1700

MHz

dB


Wideband Dipole:

|S11|2 of Wideband PCB Dipole

-15

-10

-5

0

1100 1200 1300 1400 1500 1600 1700

MHz

dB

Figure 5.1.4: |S11|2 of Wideband PCB Dipole


40

PCB Dipole Antenna

Center Frequency

Operating Band Minimum Power Reflected

Maximum Power Reflected

8mm 1355MHz 1320 – 1390 MHz 8dB 22dB

10mm 1385MHz 1320 – 1440 MHz 18dB 60dB

12mm 1400MHz 1210 – 1460 MHz 10dB 18dB

Wideband 1370MHz 1210 – 1510 MHz 5dB 14dB

Table 5.1: PCB |S11|2 Analysis

5.1.2 Error Analysis

Although all the antennas showed the expected bandwidth characteristics, it is not

operating at the ideal frequency of 1.8GHz. This error can arise from the possible

inaccurate information on the value of the dielectric permittivity, inexact etching, and

the reflected loss at the connectors.

From the readings taken, it is clear that the 10mm PCB dipole is the best impedance

matched antenna design fabricated, and the fact that in this thesis wide bandwidth is

not a requisite, the 10mm dipole were the antennas chosen for implementation of

array elements.

5.1.3 Frequency Correction on the 10mm Design

We know that the operating frequency of the antenna is dependent on the length of the

radiating element and the length of the quarter-wave matching strip by the equation

fcL

4= . Hence by, trial and error, decreasing the length of these two components I


41

was able to increase the operating frequency to the desired value of close to 1.8GHz.

The frequency correction is shown below:

Figure 5.1.5: 10mm PCB Dipole after Frequency Correction

5.2 Antenna Array Test and Analysis

In this section the performance of the array element, array power splitter and the

antenna array will be discussed and analyzed.

Decreased Length


42

5.2.1 Array Element Performance

As the array is using the corrected 10mm antenna for its radiating elements, both the

reflected power |S11|2 and the polar radiation of this antenna will be tested.

The |S11|2 test result of the 10mm antenna after frequency correction is shown below:

|S11|2 of 1.8GHz 10mm Dipole

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

1500 1600 1700 1800 1900 2000 2100

MHz

dB

Figure 5.2.1: |S11|2 of 10mm PCB Dipole after Frequency Correction

In the figure above, although the reflected power is lower than the original 60dB, the

center frequency has been corrected to 1.74GHz, which is close enough for 1.8GHz

applications.

As an anechoic chamber was not available for use in the polar radiation testing, the

test took place on the roof of the engineering building to minimize reflection. The

following illustration will show how reflections have being minimized by the placing

equipments in a diagonal configuration.


43

Figure5.2.2: Polar Radiation Test Configuration

Theoretically by using the above configuration, all power received will not have any

reflected power. However, interference was detected which affected the received

signals. These signals were most likely from “Cell C” (1.8GHz), MTN (900MHz),

Vodacom (900MHz) and the SABC (UHF and VHS).

The polar radiation test result shown indicates that the antenna designed is

omnidirectional and due to the

ground plane located behind the

radiating element, it has a lot less

back radiation as expected:

Figure 5.2.3: Polar Radiation of an Array

element

Antenna under test

Open space

Polar Radiation of 10mm 1.8GHz Dipole

0

2

4

6

8

10

0

90

180

270 Power radiated in µW


44

5.2.2 Array Power Splitter

Before connecting the four array elements on to the power splitter, the power splitter

needed to undergo the |S11|2 test to give an indication on how well it is matched.

Impedance terminators were connected to prevent power radiation at each splitter

ends. The terminator connections and the |S11|2 result are shown below:

Figure 5.2.4: Impedance Terminator Connections

|S11|2 of Array Power Splitter

-20

-15

-10

-5

0

1500 1600 1700 1800 1900 2000 2100

MHz

dB

Figure 5.2.5: |S11|2 of Array Power Splitter

Terminators


45

The result indicates that the power splitter is matched closely to the 1.8GHz region,

but not exact due to factors such as loss in connections and imprecise etching.

5.2.3 Antenna Array Performance

The array elements were connected to the power splitters by four identical length

cables (40cm) to ensure no phase change. Each array elements were positioned half

wavelength apart, as this will have enough distance so that the coupling between the

elements is minimal. Antenna array components are then attached on to a

non-reflective material called polycarbonate to ensure a minimal reflective structure.

The figure below will show how the antenna array physically stands.

Figure 5.2.6: Antenna Array


46

The |S11|2 and the polar radiation test are illustrated below:

|S11|2 of 1.8GHz Antenna Array

-25

-20

-15

-10

-5

0

1500 1600 1700 1800 1900 2000 2100

MHz

dB

Figure 5.2.7: |S11|2 of Antenna Array

Figure 5.2.8: Polar Radiation of Antenna Array

Power radiated in µW

Polar Radiation of Dipole Array

0

5

10

15

20

Power radiated in µW

0

90

180

270


47

From the |S11|2 test we see that although the impedance of the antenna array is

matched at 1.8GHz, it is better matched at a higher frequency. This is caused by the

mismatches between the array elements, and the mismatch previously determined in

the power splitters.

The polar radiation shows us that the antenna array has retained its omnidirectivity as

expected, with gain in the forward and side radiation. The back radiation in the

antenna array has also been limited; this is due to ground plane reflections from the

array power splitter. Theoretically, the antenna array will have the most gain in the

vertical region.


48

Chapter 6

Conclusions and Recommendations

This chapter discusses the conclusions that have been drawn from the results of tests

conducted on the antenna array. Recommendations are then made with regard to the

conclusions.

6.1 Conclusions

The results from the tested antenna array are satisfactory and have achieved the

objective set for this thesis, which is to design and build a high gain omnidirectional

printed circuit board dipole antenna array operating at 1.8GHz.

6.1.1 Results of Array Elements

The reflected power test (figure 5.2.1) indicates that the tested array element is

closely matched to 1.8GHz at 1.74GHz, with an excellent reflected power of 60dB.


49

The polar diagram of the power radiation (figure 5.2.3) shows that the tested array

element is radiating as a dipole antenna (omnidirectional), with the exception of

minimal back radiation. This is caused by reflections from the ground plane

connected to the antenna radiating elements.

6.1.2 Results of Array Power Splitter

The reflected power test (figure 5.2.5) indicates that array power splitter is well

matched at 1.88GHz. Although close to the 1.8GHz, but poorly matched at 1.8 GHz

exactly. This is caused by poor connections between the power splitters and the cables.

Another reason for this mismatch can be the result of imprecise etching of the

microstrip lines.

6.1.3 Results of Antenna Array

The reflected power test (figure 5.2.7) indicates that the antenna array is well matched

at 1.8GHz, but better matched at 1.95GHz. This is caused by mismatches between

each array elements and the poor matching of the power splitter.

The polar radiation test (figure 5.2.8) shows that the antenna array has retained its

omnidirectivity with the advantages of increased gain in the forward and side

radiation. Back radiation is limited due to the reflections discussed in section 6.1.1,

and the reflections from the power splitter. From the array configuration implemented,

the maximum gain theoretically occurs in the vertical region, where the polar diagram

is a test conducted for power radiation at the azimuth plane.


50

6.2 Recommendations

The following recommendations on the improvements, testing and possible

application of the antenna array have been made from the drawn conclusions. Further

testing on the current antenna array has also been proposed.

6.2.1 Improvements on the Antenna Array

The following recommendations are made to improve the performance of the antenna

array:

• Instead of printing designs on to scale 1:1 photo copies, rather give the etching

service a software form of the design. These software designs can be done in

either using “Gerber” or “Protel” software which are capable of designing

printed circuit boards. This will greatly improve the precision of etching,

hence reducing the impedance mismatches that will occur.

• The connections used between each array elements and the power splitter are

BNC connectors which were not designed specifically for 1mm PCB

boards, hence the heads needed to be physically altered to fit the boards.

Therefore for future designs, reflective loss can be greatly minimized if

connectors of the correct dimensions were used. It has also been proven that

SMA connectors are better suited for microwave applications than BNC

connectors.


51

• Back radiation can be increased for optimum omnidirectivity by altering the

position of the power splitter. Placing it below the array elements so that

reflections can be minimized on the azimuth plane.

6.2.2 Antenna Testing Recommendations

The following should be implemented to improve accuracy of the test results:

• An anechoic chamber will greatly improve the accuracy of radiation tests

conducted on antennas, as reflections are reduced.

• An automated stepping turn table would help with taking polar radiation

readings, as each reading taken will be stepped at an accurate angle.

6.2.3 Possible Antenna Array Application

As the antenna array built is omnidirectional with high gain in the vertical region, it

could be implemented in the case where ground to air communications were needed

at 1.8GHz.

6.2.4 Proposed Further Testing

The following tests and design alteration on the antenna array are proposed:

• The distance between the array elements can be altered to test for optimum

array performance.


52

• The configuration on how the array elements can be changed for different

applications, where increased antenna gain in one direction can be a trade off

for antenna omnidirectivity.

• The physical size can be reduced for commercial use. This can be done by

replacing materials used, and possible design alteration.


53

Bibliography

Sainati, Robert A. CAD of Microstrip Antennas for Wireless Applications. London:

Artech House, Inc, 1996

Chang, Kai. RF and Microwave Wireless Devices. Texas A&M University: John

Wiley & Sons, Inc, 2000.

Roddy, D. Microwave Technology. New Jersey: Prentice Hall, Inc, 1986.

Dean Straw, R. The ARRL Antenna Book. Newington: The American Radio Relay

League, 1994.

Prof. M. Reineck, university of Cape Town. Lecture notes from course EEE497C, RF

Components and Satellite Systems.


54

Appendix A

Substrate Data Sheet

The data sheet shown in this section was the information given by Northtech etching

service to help determine the characteristics of the substrate.


55


56

Appendix B

Photographs of |S11|2 Scope Displays

The |S11|2 test results were taken on a digital camera, then converted the results into

Microsoft excel format. The original photographs are shown in this section.


57

Figure B1: Photograph of Prototype Design A |S11|2 Test Result

Figure B2: Photograph of Prototype Design B |S11|2 Test Result


58

Figure B3: Photograph of Prototype Design C |S11|2 Test Result

Figure B4: Photograph of 8mm PCB Dipole |S11|2 Test Result


59




60

Figure B7: Photograph of Wideband PCB Dipole |S11|2 Test Result

Figure B8: Photograph of 1.8GHz PCB Dipole |S11|2 Test Result


61

Figure B9: Photograph of Array Power Splitter |S11|2 Test Result

Figure B10: Photograph of Antenna Array |S11|2 Test Result


62

Appendix C

Carbon Film Copies of Etched Printed Circuit Boards

Antenna designs printed on carbon films were used in the etching process. These

films are shown in this section.


63


64


65


66