DEVELOPMENT OF LOW PROFILE UNIDIRECTIONAL ANTENNA FOR
WIRELESS LOCAL AREA NETWORK APPLICATION
LWAY FAISAL ABDULRAZAK
A project report submitted in partial fulfillment of the
requirements for the award of the degree of
Master of Electrical Engineering
(Electronics & Telecommunication)
Faculty of Electrical Engineering
Universiti Teknologi Malaysia
MAY 2007
iii
To
My beloved Mother, Father, Brothers
and to
The soul of my uncle Ahmed Dawod Alsuhayl
who devoted his life towards defending Islam and our country
iv
ACKNOWLEDGEMENT
First of all, Praise to Allah, the Most Gracious and Most Merciful, Who has
created the mankind with knowledge, wisdom and power.
I would like to take this opportunity to express my deepest gratitude to a
number of people who have provided me with invaluable help over the course of my
studies.
I thank Prof. Dr. Tharek Abd. Rahman, my supervisor, for his priceless help
and advice over the course of my research, and for reviewing this thesis. His wise
suggestions have always helped me and a great number of them have gone into the
thesis.
Special thanks are dedicated to the members of Wireless Communication
Center who offered invaluable technical assistance and supports, En. Mohamed Abu
Bakar, En. Omar bin Abdul Aziz, En. Mohammed Khomeini.
My sincere gratitude and thanks also goes to those who have contributed to
the completion of this research directly or indirectly.
v
ABSTRACT
This thesis will review the project conducted the development of a low
profile unidirectional antenna for WLAN applications, performed with frequency
range 2.4-2.4835GHz. The Radial Waveguide Slot Array Antenna (RWSA) is
investigated as a low profile, significant shape, lightly weight, simple but effective,
easy to design and fabricate with reasonable cost efficient. Simulation and
optimization of structure based on Zeland Fidelity - FDTD (Finite-Difference TimeDomain) with Full-3D EM Simulation for the radiation pattern, and return loss. The
other part of this project deals with producing design relying on optimum simulation
results. The developed antenna was tested in terms of return loss, gain and radiation
pattern. Finally, integrated experimental trial had been compared with a monopole
antenna on an Access point for WLAN. Measurements are conformed to results
presented by the prototype simulation.
vi
ABSTRAK
Thesis ini akan mengulas project pembentukan antenna satu arah berprofil
rendah untuk aplikasi WLAN, dalam julat frekuensi antara 2.4-2.4835GHz. Antena
Radial Waveguide Slot Array (RWSA) telah didapati mempunyai rekabentuk yang
menarik dan ringkas, ringan, mudah dihasilkan, berkos rendah dan mempunyai nilai
gandaan yang tinggi. Simulasi dan optimasi struktur antena dilakukan menggonakan
perisian Zeland Fidelity - FDTD (Finite-Difference Time-Domain) dengan simulasi
Full-3D EM untuk menentukan corak radiasi dan nilai kehilangan balikan. Seterusnya project ini telah menghasilkan rekabentuk antena RWSA berdasarkan hasil
simulasi yang paling optimum. Kehilangan balikan, gandaan dan juga corak radiasi
antena yang dihasilkan telah diukur dan dibandingkan dengan antena satu kutub bagi
aplikasi ‘Access point’ untuk WLAN. Pengukuran didapati bertepatan dengan hasil
simulasi yang diberikan oleh perisian Zeland Fidelity.
vii
CONTENTS
CHAPTER
TITLE
TITLE
i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
CONTENTS
vii
LIST OF TABLES
xi
LIST OF FIGURES
xii
LIST OF ABBREVIATIONS
xv
LIST OF APPENDICES
I
PAGE
xvii
INTRODUCTION
1.1
Introduction
1
1.2
Problem Statement
2
1.3
Objective
2
1.4
Research scope
3
1.5
Research Methodology
3
1.6
Thesis Outline
6
viii
II
WIRELESS LOCAL AREA NETWORK AND
RADIAL WAVEGUIDE SLOT ARRAY ANTENNA
III
2.1
Introduction
7
2.2
Wireless LAN background
7
2.3
Indoor hot spot WLAN service and outdoor
last-mile broadband access
9
2.4
IEEE 802.11b/a/g Standards
11
2.5
Comparing the Wireless Standards
12
2.6
RWSA Evaluation
15
2.7
Introduction to RWSA
15
2.8
Single-Layer RWSA Antenna Design
18
2.9
Problem Configuration of RWSA
21
2.10
General Theoretical Consideration
22
2.10.1 Model of single slot
22
2.10.2 Model of slots’ assembly in radial line
23
2.11
Small RWSA Antenna
26
2.12
Summery
28
RWSA ANTENNA DESIGN AND SIMULATION
MODELLING
3.1
Introduction
29
3.2
Antenna Structure
30
3.3
Initial Calculation Results
33
3.4
Finite Difference Time Domain (FDTD) Simulation 35
3.5
Antenna Simulation Modeling
37
3.6
Antenna Design and simulation results
40
3.7
Simulation results
41
3.8
Radiation pattern
41
3.9
Return loss Various Frequencies
42
3.10
Comparison between this design and previous
design
43
ix
3.11
IV
Summary
44
FABRICATION AND MEASUREMENTS
4.1
Introduction
45
4.2
Antenna Prototype
45
4.3
Antenna Measurement Setup
48
4.4
Return Loss Measurement Result for the first
Design
4.5
4.6
48
RWSA 2.4 GHz Simulations and Prototype
(first design) Measurement Comparison
49
Second design
49
4.6.1 Introduction
49
4.6.2
49
Theoretical ideas and solutions
4.6.3 Second design structure
50
4.6.4
Comparison between the 1st & 2nd design
51
4.6.5
Return Loss Measurement Result for the
Second Design
4.6.6
52
Comparison between the First and the
Second design Parameters
4.6.7
Comparison between the RWSA second design and
4.6.8
the simulation results biases on the Return Loss
4.6.9
RWSA 2.4 GHz Simulations and Prototype
52
53
(Second Design) Measurement Comparison
53
4.7
Radiation pattern measurements
54
4.8
RWSA antenna Gain Result over deferent
Frequencies
56
4.9
Received Signal Strength Index
57
4.10
Summery
59
x
V
CONCLUSION AND SUGGESTIONS FOR FUTURE
WORK
5.1
Conclusion
60
5.2
Suggestions for Further Work
61
REFERENCES
63
APPENDICES
66
xi
LIST OF TABLES
TABLES
TITLE
PAGE
2.1
802.11a vs. 802.11b vs. 802.11g
12
3.1
Initial calculation results based on 5.2 GHz antenna prototype
33
4.1
antenna parameters comparison for simulation and prototype for
First design
47
4.2
RWSA 2.4 GHz simulation and prototype measurement comparison
49
4.3
antenna parameters comparison for simulation and prototype
51
4.4
antenna parameters comparison for 1st & 2nd design prototype
51
4.5
RWSA 2.4 GHz simulation and prototype measurement comparison
54
xii
LIST OF FIGURES
FIGURES
1.1
TITLE
PAGE
Flow chart representing a unified design of RWSA antenna
5
2.1. a WLAN topology for ad-hoc mode
9
2.1. b WLAN topology for infrastructure mode
9
2.2
A circular slot formed by a multiplicity of short linear slots
16
2.3
Annular slot aperture and space geometry
16
2.4
Radial wavegide slot waveguide array (a) double layered, (b) single
layered
2.5
single layer RWSA with different feeds (a) probe feed, (b) recessed
cavity feed
2.6
19
20
Schematic presentation of the single-layered linear-polarized RWSA
antenna with its principal elements
21
2.7
Common slot geometry of linear-polarized RWSA antenna
22
2.8
equivalent electrical lumped-circuit model of slot in thin metallic plate
22
2.9
For the TEM two-plate guide
23
xiii
2.10
Ringed segment of radial line for its presentation by transmission
line model
2.11
Equivalent transmission line model of slots’ assembly in the radial guide
forming RWSA antenna aperture like quasi-periodic radial structure
2.12
24
25
Equivalent electrical features of slotted radial line where quality factor
Q as parameter above is determined by slot geometry namely
25
2.13
CP RWSA antenna proposed by Zagriatski and Bialkowski
27
3.1
R WSA antenna structure
30
3.2
The radiating surface of the RLSA antenna is formed by 4 discrete slots
arranged at tangent of the array radius
31
3.3
RLSA antenna structure shorted probe (lower layout)
32
3.4
Insertion of coaxial monopole SMA connector into the slotted radial
waveguide through the backing plate
3.5
32
Simulation domain in 3D outline view, which shows the antenna structure
and the space boundaries
38
3.6
Object list to define the antenna structure
39
3.7
3D view of the antenna structure, built in FIDELITY. The structure is
meshed into small rectangular cubes
40
3.8
Radiation pattern of the 2.4GHz RWSA antenna design
41
3.9
2.4GHz RWSA Antenna Radiation Pattern viewing from (a) z plane
and (b) y plane
42
xiv
3.10
Return loss in case of polypropylene as radial waveguide cavity
43
3.11
Comparison between this design and previous design [33]
43
4.1
The R WSA antenna prototype structure
46
4.2
Return loss result for R WSA first design antenna prototype
48
4.3
Return loss result for R WSA second design antenna prototype
52
4.4
Comparison between the First and the Second design Parameters
52
4.5
Return loss result Comparison between the second design and the
simulation results
53
4.6
direction of E-field, and the direction of H- field for the single slot
54
4.7
Rotating degree during the Radiation field pattern measurements at
00, 45o, and 90o
54
4.8
Radiation Pattern at 00
55
4.9
Radiation Pattern at 450
55
4.10
Radiation Pattern at 900
56
4.11
antenna gain under different frequencies
57
4.12
RSSI Comparison between RWSA antenna and RSSI of the monopole
antenna using AirMagnet for a short distance
4.13
58
Comparison between the RSSI of the RWSA antenna and RSSI of the
monopole antenna using AirMagnet for a Long distance
58
xv
LIST OF SYMBOLS
2D
-
Two dimension
3D
-
Three dimension
εeff
-
Effective dielectric constant
εo
-
dielectric constant of free space
εr
-
dielectric constant / permittivity
λ
-
wavelength
λg
-
guided wavelength
λo
-
free space wavelength
μo
-
Permeability of free space
c
-
velocity of light
D
-
directivity
dB
-
decible
f
-
Frequency
b
-
Radial Cavity Hight
IL
-
Insertion Loss
L
-
Inductance
Pi
-
Incident Power
Pmax
-
Peak handling Capacity
Pr
-
Reflected Power
Pt
-
Transmited Power
R
-
Resistance
RL
-
Return Loss
TEM -
Transverse Electromagnetic
V
Voltage
-
xvi
ρa
-
Slot Array Radius
ρ sc
-
Short circuit distance
ρw
-
waveguide radus
Ls
-
ws
-
slot width
Zo
-
chaecteristics impedance
slot length
xvii
LIST OF APPENDICES
APPENDIX
TITLE
PAGE
A
Antenna Prototype Dimensions
65
B
Antenna Measurement Setup
69
C
RSSI SETUP
70
D
Matlab Code for Radiation Pattern Graphs
71
CHAPTER I
INTRODUCTION
1.1
Introduction
Antenna designers are always searching for ways to improve existing designs
or introduce novel designs in order to achieve desirable radiation characteristics,
reduce the size and weight, which are mandatory requirement for antennas used in
WLAN and thus make antennas more cost efficient [1].
Return loss, axial ratio, gain, bandwidth and received signal strength are
some of the important properties which are improved.
The recent explosion in information technology and wireless communications
has created many opportunities for enhancing the performance of existing signal
transmission. An indispensable element of any wireless communication system is the
antenna. Transmission of data at higher rates requires adequate bandwidth for the
elements constituting a communication link accordant to IEEE802.11b/g standard
which well-handled in this project [2].
For WLAN applications, where problems such as multi-path fading due to
reflections from various scatters occur, a linearly polarized RWSA antenna is a
preferable option. The reason is that this polarization enhances overall system
diversity and permits freedom of orientation for the user-end antenna [3].
2
Radial waveguide slot array Antennas (RWSA) is very attractive for
applications in communication devices for wireless local area network (WLAN)
systems in the 2.4 GHz (2400–2484MHz), the free Industry-Scientific-Medicine
(ISM) frequency band [4]. Work investigated on development of the low profile
unidirectional Radial Waveguide Slot Array Antenna as a potential alternative to the
WLAN AP antenna.
1.2
Problem Statement
The problem statement of this project is stated in the follow: WLAN users
often complain of poor signal coverage. Therefore, an antenna with High gain and
directivity suitable for indoor and outdoor WLAN in 2.4GHz ISM band is required,
other point is the importance of obtaining a satisfactory coverage can not be over
emphasized.
Theoretical results are obtained to satisfy good return loss requirements and
specific radiation pattern shapes for the RWSA antenna, but the practical result is
still big challenge to be verificated and prove that down-to-earth.
1.3
Objective
The proposed project proposes a development of the low power profile for a
unidirectional antenna depending on Radial Waveguide Slot Array Antenna
(RWSA), which is attractive for point-to-multipoint point communications, linear
polarized small RWSA antenna as an external antenna for access point of WLAN
based on IEEE 802.11b/g standard, and the simulation design will done according to
the Federal Communication Commission (FCC) regulations, by depending on the
simulation results prototype will be doe and tested in Lab, and test bed as a field trial.
3
1.4
Research Scope
The Research introduces:
1. WLAN protocols such as IEEE 802.11a/b/g free ISM band for which RWSA
antennas are aimed to be designed.
2. The antenna specifications include parameters such as frequency, bandwidth,
polarization, gain and all theoretical investigations.
3. Following that the simulation tools for antenna design based on Zeland
Fidelity, FDTD, with Full-3D EM Simulation for the radiation pattern will be
introduced.
4. Using of the linear polarization to improve the antenna gain.
5. Simulation of the Radiation pattern until reach the best result, and compare
with previous design in field pattern and return loss result.
6. simulation result should be proven for indoor WLAN then outdoor WLAN
7. The prototype will be produced based on the simulation to involve the design
and development of the low profile antenna; it will be tested in Lab and test
bed as a field trial to measure the antenna performance.
8. Comparison of measured prototype with simulation.
9. Report / Thesis writing.
1.5
Research Methodology
A reactive theoretical and experimental design approach was utilized to
optimize the antenna structure, the strategy implemented for simplifying the design
and development procedures in this research work can be divided into the following
points:
1. initial concept
•
literature review
•
problem statement
•
design conceptual understanding
4
2. Design and simulation stage
•
Slot pattern design and desired radiation pattern and polarization.
•
Antenna input impedance.
•
Compare between this design and previous design.
3. Prototype stage
•
Antenna fabrication.
4. Measurement stage.
•
Radiation pattern.
•
Return loss.
5. Analysis stage.
•
Comparison between the measurements and the simulation results.
The antenna fabrication needs to fit within the costing constraints and the
availability of materials. The design and development procedures are briefly
summarized in the following chart Figure 1.1 in particular, this methodology
provides an approximate chronological progress of the work performed to finally
complete the full design cycle.
Initial antenna design specifications
(Gain, Frequency, Polarization)
Determine antenna diameter, and Chose
feed type (probe feed, recessed cavity)
Simulation using an electromagnetic analysis tool for:
• E-Plane and H-Plane radiation pattern.
• Return loss/VSWR.
• Polarization.
5
Generate slot pattern layout details
Model radiation pattern for obtained
slot layout
Change offending
parameters based
on experimental
findings
Suitable
radiation
pattern?
No
Yes
Produce physical radiating surface and
adhere to radial cavity
Perform experimental evaluation (return
loss, gain, radiation, aperture profile)
No
Design
specification
met?
Yes
Design complete!
Figure 1.1: Flow chart representing a unified design of RWSA antenna.
6
1.6
Thesis Outline
Chapter 1: Consists of introduction of the project. Brief General Background
is presented. The objectives of the project are clearly phased with detailed. The
research scope and methodology background are also presented.
Chapter 2: Includes section1 of the literature review, introduction to the
wireless communication, begins with an overview of indoor and outdoor contents
then IEEE standard. Radial Waveguide slot array antenna evaluation and general
description to the profile structure characteristics and its type also presented with
theory background, historical development.
Chapter 3: Design and simulation modeling for the antenna, provides
descriptions of the initial calculation results of the model and techniques for the finite
difference time domain, design and simulation results, compare the result with the
previous design.
Chapter 4: Presents the results of antenna prototype measurements and apply
the antenna in the real environment, starting with the indoor application then applied
the RWSA antenna outdoor.
Chapter 5: Concludes the thesis. The conclusion is given based on the
analysis of results from the previous chapter and suggestion for future research.
CHAPTER II
WIRELESS LOCAL AREA NETWORK AND RADIAL WAVEGUIDE SLOT
ANTENNA
2.1
Introduction
Wireless Local Area Network (WLAN) applications are new, fast growing
telecommunication protocols operating mainly in a free Industry-Scientific-Medicine
(ISM) frequency bands. The choice of free frequency bands make then very
attractive from commercial point of view. The systems require suitable antennas for
point to multipoint communications. In order to attract the commercial market, these
antennas have to feature low manufacturing cost and pleasing aesthetic appearance.
Radial Waveguide Slot Array (RWSA) antennas seem to provide such required
features [2]. So far, the design, development of these low-cost and low-profile
antennas have been for satellite communications. In this case, the RWSA antenna has
to feature moderate to high gain. The present research focuses on the design and
development of Radial waveguide Slot Array antenna for Wireless Local Area
Network applications in indoor environment.
2.2
Wireless LAN Background
Wireless Local Area Network (WLAN) is a Local Area Network in which the
information is sent and received using Radio Frequency (RF) technology. WLAN
enables high bandwidth and mobility inside its coverage area and makes the
8
construction of the network easier because the need of cabling is omitted. A number
of different WLAN standards exist.
There are two types of wireless communication network; one is the cellular
network, evolved from mobile telephone, and the other is the wireless local area
network, emerged from computer network. Wireless network technologies were
uninteresting (and immature) for years until 1985 when the Federal Communications
Commission (FCC) of the United States authorized the Industrial, Scientific and
Medical (ISM) frequency bands. These three ISM bands accelerated the development
of WLANs because vendors no longer needed to apply for licenses to operate their
products [4].
In 1989, the IEEE 802.11 Working Group began elaborating on the Wireless
LAN Medium Access Control and Physical Layer specifications. The final draft was
ratified on 26 June 1997. The IEEE 802.11 standard defines what comprises a Basic
Service Set (BSS). That is, the set has two or more fixed, portable, and/or moving
nodes or stations that can communicate with each other over the air in a
geographically limited area. Two configurations are specified in the standard: ad-hoc
and infrastructure. The ad-hoc mode (see Figure 2.1.a) is also referred to as the peerto-peer mode or an Independent Basic Service Set (IBSS). This ad-hoc mode enables
mobile stations to interconnect with each other directly without the use of an access
point. All stations are usually independent and equivalent in the ad-hoc network.
Stations may broadcast and flood packets in the wireless coverage area
without accessing the Internet. The ad-hoc configuration can be deployed easily and
promptly when the users involved cannot access or do not need a network
infrastructure. For instance, participants of a conference can configure their laptops
as a wireless ad-hoc network and exchange data without much effort.
In the infrastructure mode (see Figure 2.1.b) there are access points which
bridge mobile stations and the wired network. BSSs can be connected by a
distributed system that normally is a LAN. The coverage areas of BSSs usually
overlap. Handoff will happen when a station moves from the coverage area of one
access point to another access point. Although the radio range of a BSS limits the
9
movement of wireless stations, seamless roaming among BSSs can construct a
campus-wide wireless network service [5].
Figure2.1.a: WLAN topology for ad-hoc mode.
Figure2.1.b: WLAN topology for infrastructure mode.
2.3 Indoor Hot Spot WLAN Service and Outdoor Last-mile Broadband Access
Hot spot service provides indoor public wireless access to the Internet,
typically in airports, coffee shops, restaurants or hotels. On the other hand, the lastmile broadband access is similar to the wireless local loop (WLL). Instead of the
10
expensive fixed networks, W-ISPs bridge their customers through the air with a large
coverage. Even so, WLAN last-mile services are still rarely deployed.
In general, an indoor wireless local area network (WLAN) consists of
wireless access points (APs) and user-end terminal equipments with WLAN network
interface cards (NICs), such as personal computers (PCs) and handheld devices
(notebooks, personal digital assistants (PDAs), cellular phones, etc.), to easily access
data and gain information anywhere in the inside area.
Since the indoor wireless AP as a hotspot is capable of providing network
interconnection, building an inside wireless networking is easy if the wireless APs
are of sufficient amount and are distributed uniformly in the indoor area. In recent
year, however, the requirement for the network accessing service has expanded from
the indoor area to the outdoor environment, so as to support better coverage of
network accessing areas and to provide more efficient and convenient data access
link services for people to support ubiquitous network applications [6]–[7]. However
due to the free space loss in wireless data transmission, it is hard to maintain the
overall signal quality in a large transmission range in outdoor environment. Hence,
the outdoor wireless network is quite different from the indoor wireless network
which can be built and realized easily.
The deployment of wireless APs is especially critical in the outdoor
environment to provide good signal quality in data communication for users [8]–[9].
On the other hand, the security certifying mechanism of authentication,
authorization, and accounting (AAA) in wireless networks is also an important issue
to improve the networking quality in support of reliable, open, secure, and flexible
mobile service accesses [10]–[11]. In order to further enhance the performance of
AAA servers, a service-oriented AAA architecture and a peer-to-peer authentication
and authorization mechanism are proposed in [11] and [12], respectively, for
enhancing the service ability in specific service needs and for minimizing
authentication delays when mobile users roam across different wireless networks.
11
2.4
IEEE 802.11b/a/g Standards
The IEEE 802.11 standard proposed in 1997 was a milestone for WLANs.
But two years later on 16 September 1999, the IEEE 802.11 standard was officially
revised. The new standard, still operating on the 2.4 GHz frequency band, is called
802.11b or 802.11 High Rate. The 802.11b standard provides a data rate up to 11
Mbps, which is comparable to a fixed Ethernet. It is a more robust system but still
accommodates the same 802.11 protocols. The IEEE 802.11b physical layer adopts
Complementary Code Keying (CCK) technology such that upgrading can be done
easily. While the data rate goes to 11 Mbps, it has fallback rates of 5 Mbps, 2 Mbps,
and 1 Mbps. The 802.11b uses the same bandwidth as the original 802.11 Direct
Sequencing Spread Spectrum (DSSS) physical layer. Backward compatibility thus
can be ensured. Besides, the coexistence of the 11 Mbps 802.11b system and the 2
Mbps 802.11 system permits a smooth transition to a faster WLAN system. Although
802.11b products have successfully conquered the WLAN market, the resulting
interference within the 2.4GHz ISM band is a major issue. Not only Bluetooth
devices, but also many medical equipment and household appliances (e.g. microwave
ovens and cordless telephones) use the 2.4 GHz frequency band. Therefore, the IEEE
802.11a standard was approved in September 1999 that instead uses the 5 GHz
frequency band. This band change implicitly implies that 802.11a and 802.11b are
not compatible.
What hinders the progress of 802.11a is not only the incompatibility with
today’s 802.11b products, but that the 5 GHz spectrum is not license-free in every
country. Therefore, the IEEE proposed the 802.11g standard in November 2001 to
enhance the 2.4 GHz 802.11b technology. 802.11g defines two optional modulations.
The Packet Binary Convolution Code (PBCC) modulation optionally supports
22Mbps and 33Mbps for payload data rate. Another optional modulation, OFDM,
supports at most 54Mbps payload data rate. In addition, compatibility with 802.11b
products is promised. The 802.11g standard was ratified on 13 June 2003. Products
based on its early drafts are available on the market already [5].
Typically a WLAN network consists of the following core components:
12
1. A WLAN access point (AP), which broadcasts messages on a certain
frequency and listens for responses from its clients.
2. The WLAN access card is the client interface that talks to the access point.
WLAN can be set up using so called ad hoc topology, in which the clients
send and receive messages between each other instead of through the access point.
The WLAN access point can provide a sufficient connection from a 30 to 50 meter
indoor location, giving the users the freedom to move within the coverage area. We
can build a WLAN in the areas where it is not wise or even possible to provide a
gateway using the normal cabling, e.g. telephone line, DSL line or optical fiber. We
can also have a “mobile” WLAN wit h a connection to other data networks.
2.5
Comparing the Wireless Standards
Table 2.1: 802.11a vs. 802.11b vs. 802.11g.
Wireless Standard
Frequency
802.11a
802.11b
802.11g
Wireless Standard
Wireless Standard
Wireless Standard
5 GHz Underused 5
2.4 GHz Heavily
2.4 GHz Heavily
GHz band can
used 2.4 GHz
used 2.4 GHz band.
coexist with 2.4
band. Interference
Interference from
GHz networks
from other 2.4
other 2.4 GHz
without
GHz devices such
devices such as
interference.
as cordless
cordless phones,
phones,
microwave ovens,
microwave ovens,
etc. may occur.
etc. may occur.
Speed
54 Mbps 5X greater
than 802.11b.
11 Mbps Cable.
54 Mbps 5X
greater than
802.11b.
13
Channels / Non
12 / 8
11 / 3
11 / 3
overlapping
Range (Range will
Shorter range than
Better range than
Better range than
depend on antenna
802.11b and
802.11a. 2.4 GHz
802.11a. 2.4 GHz
gain, transmit power, 802.11g. Due to
signal travel
signal travel
the receive
higher operating
farther, and can
farther, and can
sensitivity of the
frequency, typically
work through
work through walls
radio card and any
offers less range and walls and floors
and floors more
obstacles between
is less capable of
more effectively
effectively than 5
path ends).
working through
than 5 GHz
GHz signals.
wall and floors.
signals.
Incompatible with
Widely adopted.
Backwards
802.11b or 802.11g.
Will work in
compatible with
Compatibility
802.11g networks. 802.11b networks
(at 11 Mbps);
Incompatible with
802.11a.
Popularity
User base still
Currently has the
Latest ratified
relatively small.
largest user base.
standard. With
Limited selection on 802.11b is currently speeds up to 5
802.11a equipment.
used in most hot
spots including
airports, hotels,
campuses, and
public areas. Wide
selection of 802.11b
equipment.
times faster than
802.11b, Expect
this standard to
overtake 802.11b
as the standard of
choice.
14
Cost
Most expensive
Cheapest
tomorrow
Since this
standard's
ratification, prices
have dropped
significantly.
Pricing is
competitive with
802.11b. Cheaper
than 802.11a
Benefits
Excellent speed,
Largest user base,
The speed of
unaffected by 2.4
cheapest, used in
802.11a with the
GHz devices, can
most public hot
range of 802.11b,
co-exist with
spots, largest user
compatible with
802.11b and
base, wide
802.11b networks
802.11g networks
selection of
and hotspots,
without interference equipment
affordable
Wireless communications are becoming important for business and private
use, a wireless requires efficient and high gain antenna at low cost, microstrip
antennas are attractive in wireless communication because of light weight, low
profile and compatibility with Microwave Monolithic Integrated (MMIC) circuits.
However one of the major disadvantages is low gain. Annular slot array antenna
enjoys all the advantages of planar structure, while they have high gain.
In this research, WLAN is based on the IEEE 802.11 b\g standard in the
2.4GHz band. For 802.11b compatibility, 802.11g incorporates 802.11b’s
complementary code keying (CCK) to achieve bit transfer rates of 5.5 and 11 Mbps
in the 2.4 GHz band. In additional, 802.11g adopts 802.11a’s orthogonal frequency
division multiplexing (OFDM) for 54Mbps speeds but in the 2.4GHz range.
15
2.6
RWSA Evaluation
The radial waveguide slot array antenna is formed by a thin circular disk-
shaped plastic body, which is enclosed in a conductive coating or foil material. In the
standard RWSA design, the upper circular conductive surface carries a defined
distribution of radiating slots, while the rear conductive surface is devoid of any
slots. This rear surface incorporates a coaxial feeding element at its centre. Much
interest has developed over recent years in this antenna because of its potential to
overcome a number of the problems associated with its competitors, such as a
parabolic reflector antenna or a planar Microstrip patch array. Investigations are
performed both into linearly and circularly polarised antennas.
Slot antenna technology using narrow slots in planar conductors can be used
to achieve a flat antenna design; a natural way of feeding slot arrays is by using
waveguides. Because of low conduction and dielectric (mainly air dielectric is used)
losses attainable in such structures, the resulting gain of a slot array antenna is
usually higher than that of the same size microstrip patch array.
Another advantage is its high power level handling capabilities. Similar to
microstrip patch arrays, different pattern configurations and feeding/combining
methods can be applied to develop slot arrays. The simplest case is a onedimensional array formed by a rectangular waveguide with slots appearing at regular
intervals in its surface. In this case, a rectangular waveguide accomplishes a series
circuit-type combiner.
2.7
Introduction to RWSA
At the end of the 1950s, Kelly [13] proposed a radial waveguide as a feeding
network for a two-dimensional distribution of slots and demonstrated its use in the
early 1960s. [14, 15]
In 1964, Kelly et al. [16] introduced the annular slot
monopoles planar arrays with linear polarization which was limited only to the 900
16
sectoral radial waveguides instead of a full radial waveguide. This model has its
feeding mode controlled to give an arbitrary polarization.
Figure 2.2: A circular slot formed by a multiplicity of short linear slots.
Figure 2.3: Annular slot aperture and space geometry.
Goto and Yamamoto [17] were the first to propose the commercial use of
RLSA operating in a traveling TEM wave excitation for 12 GHz band. They
suggested a novel high gain planar antenna having a circularly polarized double
layered-RLSA. A double-layered RLSA was a double fold radial waveguide consists
17
of slots arrays arranged in spiral on the upper waveguide and a feeding structure at
the centre of the lower waveguide as demonstrated in Figure 2.4. Ando et al. [18] has
since then investigated extensively in the double-layered RLSA.
The concept known as a radial waveguide slot array (RWSA) antenna is very
attractive because only a single waveguide, instead of its multiple, is used as a
feeding network to a two-dimensional distribution of slots. In its original
construction, a circular waveguide supporting a TE 11 mode fed a slotted radial
waveguide using a suitable transition located on the side devoid of slots. The desired
antenna polarization (linear, circular, or elliptical) was attained via the choice of
circular-to-radial guide transition and a suitable distribution of slots. In the original
design, concentric annular arrays of crossed slots were used. In 1980, Goto and
Yamamoto [19] proposed the modified concept of the slotted waveguide antenna by
Introducing an alternative slot arrangement that would allow for circular polarization
to be obtained from a double layer radial cavity, fed by a simple probe feeding
structure centrally located in the lower level of the double-layer cavity.
The slot arrangement on the upper cavity surface took the form of a spiral
array; each element in the array consists of two slots, spaced so as to be phased in
quadrature, hence forming a unit radiator of circular polarization. This proposed
antenna had removed the complexity of the feed structure, but had added a
manufacturing complexity resulting from its double-layered nature; this addition was
necessary for maintaining constant amplitude aperture illumination, requiring an Ebend to get the radiated field to and from the upper and lower cavities.
A simplified single-layer structure proposed by Takahashi et al. [20] is
suitable for overcoming the manufacturing complexities brought about by the
double-layer cavity design, but introduces the problem of an intolerably tapered
aperture illumination profile resulting from the naturally decaying outward traveling
radial wave in the feeding cavity. Single- and double-layer versions of this antenna
including both circular (CP) and linear polarization (LP) cases have since been
introduced and investigated in the literature. Figure 2.4 shows the construction
details of single- and double-layer RWSA antennas introduced in the literature [2122].
18
Many Advantages of the single-layer RWSA antenna include potentially high
radiation efficiency; extremely low profile; ease of installation; and immunity to leaf,
water, and snow buildup as a result of its flat surface. Despite this remarkable
flexibility, there is, however, an inherent flaw in this RWSA antenna performance
when linear polarization is required.
2.8
Single-Layer RWSA Antenna Design
In its standard form the antenna consists of two plates spaced a distance d
apart, with the upper plate bearing the radiating slot pattern, and the rear plate left
unmodified. The radial guide formed between these plates is filled with a dielectric
material of relative permittivity
εr >1 (in practice, between 1.5 and 2.5) to avoid
grating lobes in the radiation pattern.
The operation of the antenna can be considered in either receive or transmit
modes of operation. Both are equally as valid because of the reciprocity theorem. In
the transmit mode of operation, the signal fed to the antenna via the coaxial cable is
launched by the feeding mechanism into an outward traveling axially symmetrical
wave inside the radial cavity.
The area of radius
ρ min
around the feed probe is left devoid of slots to allow
the formation of an axially symmetrical traveling wave. In turn, this cavity mode is
coupled into a radiated free-space wave via the slot pattern on the upper cavity
surface. Depending on the slot orientation and positioning, different types of wave
polarization can be radiated (linear, circular, or elliptical). Any residual power not
coupled by the slot pattern is lost in the cavity termination. The realization of a given
coupling function is achieved by using the theory of a single slot in a waveguide
[23]. By including other factors, such as avoiding slot overlap, the slot location,
orientation, and length are obtained in the form of a computer algorithm.
19
Figure 2.4: Radial waveguide slot waveguide array (a) double layered, (b)
single layered.
The output data can be used to theoretically model the radiation pattern prior
to the realization of the antenna. Alternatively, the output data is used to generate a
physical layout of the radiating surface, ready for computer-aided manufacture. To
overcome the inherent poor return loss performance, the LP RWSA antenna radiating
surface includes additional (reflection canceling) slots. An alternative solution
involves tilting of the main beam direction, [24, and 25] which does not require
introducing additional slots. Irrespective of the method, the final result is a slot
pattern, which produces high return loss at the feed point. The computer algorithm
developed to predict the radiation pattern of a given pattern of slots aids this process.
In this pattern-modeling approach, each radiating slot is replaced by an
equivalent magnetic dipole and the field pattern resulting from an entire set of slots
in the radiating surface is obtained using the principle of superposition. The slot
20
excitation coefficients are obtained in an approximate manner using a small coupling
theory of slots. The developed computer algorithm produces plots of the radiation
pattern of the RWSA antenna in an arbitrarily chosen plane.
Figure 2.5: single layer RWSA with different feeds (a) probe feed, (b) recessed
cavity feed.
Some experimental research series have been performed to confirm the
validity of the proposed theoretical concepts and to research experimentally some
aspects of studied problems. Compact antenna range assembly based on the analog
network analyzer has been employed. Presented data results from considerable
theoretical and experimental studies conducted by the author since 1990.
21
Problem Configuration of RWSA
Figure 2.6 shows the usual basic configuration of linear-polarized RWSA
antenna that is some in general features for the well-know X-band antennas [11, 26],
and millimeter-waves ones. Note that the millimeter-waves RWSA antenna has some
construction peculiarities concerning implementation of its principal components
like: 1) the radiating aperture formed by the upper plate of radial line with definite
slot topology performed on dielectric substrate by etching process; 2) the lower plate
of radial line served simultaneously as antenna construction base for its easy
handling and installation; 3) antenna feeding unit included two transitions, i.e.
‘rectangular guide - coaxial’ and ‘coaxial - radial line’. Shortly speaking, the RWSA
antenna operates like a traveling wave antenna with gradually decaying outward
wave, which starts from feeding point and excites consequently each partial linearpolarized radiator formed by pair of slots in common mode [11, 26].
Figure2.6: Schematic presentation of the single-layered linear-polarized
RWSA antenna with its principal elements: 1) upper radiating plate with slots on
dielectric substrate with metallic thin sheet; 2) conical launcher of radial line; 3)
matched edge load; 4) waveguide feeder; 5) antenna base and lower radial line plate;
6) slow-wave dielectric material.
22
Figure2.7: Common slot geometry of linear-polarized RWSA antenna.
(Figure2.7) to get dominant linear polarization, an electromagnetic coupling
between slots and radial outward wave produces definite amplitude-phase
distribution of field over aperture resulted finally in some antenna radiation
performances obtained.
2.10
General Theoretical Consideration
2.10.1 Model of Single Slot
Figure 2.8: equivalent electrical lumped-circuit model of slot in thin metallic plate.
23
An equivalent electrical lumped-circuit model of single slot (Figure2.8) is
starting point for the RWSA analysis [5]. This equivalent circuit with evident
resonance features characterized by resonance frequency f0 and quality factor Q [27]
is shown in Figure 2.8.
Figure 2.9: For the TEM two-plate guide.
The next step of analysis involves formal description of slot frequency
behavior in a transmission line like in note that some correction of slot’s length is
necessary due to edge radiation effect, Figure 2.9 equivalent transmission line model
of slot in the TEM two-plate guide.
It was established by the author that an approximated slot’s analysis based on
wave matrix model is productive in practice for considered problem. The basic idea
implemented here is one that slot’s influence on propagation features of waveguide
fundamental mode, i.e. TEM mode in this case, can be outlined as modification of
waveguide impedance and its wave propagation factor, which become frequencydepended, i.e. disperse and complex [28].
2.10.2
Model of Slots’ Assembly in Radial Line
Some specific properties of radial line [29] should be involved in study too. A
radial line is treated here by its ringed-segment parts as shown conditionally in.
24
exp(− j.β .d )
⎡
⎢
1 + d / Ro
T= ⎢
⎢⎣ 1 + d / Ro . exp(− j.β .d )
exp(− j.β .d ) ⎤
1 + d / Rb ⎥⎥
⎥⎦
0
The T-matrix as any wave matrix for radial-line requires special cares
concerning wave amplitude decreasing due to natural radial-wave outward
propagation. Such formal approach is preferable thanks the fact that it allows inside
framework of single mathematical model to compute all necessary values to
characterize antenna internal features like return-loss and external one as radiation
pattern and efficiency.
Figure2.10: Ringed segment of radial line for its presentation by
transmission line model.
Each segment is described by the T transmission matrix: In the radial-patch
model proposed an amplitude-phase distribution of electromagnetic field over round
aperture to achieve necessary radiation features is determined as superposition of all
radial subsections (Figure 2.10). In turn, amplitude-phase distribution of each
subsection is determined by voltage drop on it that is difference between its input and
output voltage for outward wave Frequency dependence of the T-matrix RWSA
model gives possibilities to estimate antenna total frequency response in the
operation frequency band.
25
Figure 2.11: Equivalent transmission line model of slots’ assembly in the
radial guide forming RWSA antenna aperture like quasi-periodic radial structure.
In accordance to discussed model, the slot-disturbed aperture of radial line
can be described via properties of equivalent transmission line that includes such
factors like
Figure 2.12: Equivalent electrical features of slotted radial line where quality
factor Q as parameter above is determined by slot geometry namely.
26
(Figure 2.12): 1) slow wave coefficient that modified effective wavelength in
radial line and slots’ spacing, 2) aperture coupling factor, i.e. leakage constants,
which determines the effects of power take-off by slots from traveling outward wave
that resulted in aperture field distribution, 3) phase of slot’s voltage drop that is
actual to maintain in-phase aperture field distribution. All these values are important
for the aperture synthesis procedure considered above to obtain slotted aperture
geometry for given pattern and radiation antenna requirements.
2.11
Small RWSA Antenna
The present invention relates to the antennas formed by an array of radiating
slots made in a wall of a set of microwave signal feeder or collector waveguides
positioned side by side. Antennas of this kind are well known in the prior art
especially for their ability to be aimed by phase shifts or frequency variation of the
microwave signals traveling through their waveguides.
The RWSA has been proven to be effective in the high gain applications like
point-to-point microwave link and direct broadcasting satellite services., however not
many has research into the RWSA for indoor WLAN applications which is' of lower
gain and having a broader beamwidth. In order to produce a less directive broad
beam antenna, the RWSA antenna will have less annular slots and therefore forming
a smaller RWSA antenna.
As we have seen, the different elements forming the structure of the antenna:
the radiating and stiffening plates as well as the chutes form part of the technology of
printed circuits. Like the printed circuits, they are formed by woven or unwoven
sheets of dielectrical materials, often based on fiber composites of thermoplastic or
thermohardening glass-resin, lined if need be with a metallization. Hence, no
mention has been made of the use of bonder during the assembling. However, it is
possible to use bonders during assembling to improve the adhesion between layers or
quite simply to obtain adhesion between layers when the resin used is not
thermoplastic but simply thermohardening.
27
In the same way, only copper-based metallization have been mentioned but it
is clear that metallization based on other materials may be envisaged, especially
those based on all the metals and alloys used in microwave applications
Few publishes have discussed about the small aperture RWSA analysis.
Takashi et al. [30] and Zagriatski and Bialkowski [31] examining on the circularly
polarized small aperture RWSA. Figure 2.13 shows the prototype by Bialkowski.
Figure 2.13: CP RWSA antenna proposed by Zagriatski and Bialkowski.
Tharek and Farah [32] analyzed on the linearly polarized small aperture
RWSA at 5.5GHz band based on IEEE 802.1 la standard.
L.M. Choong, have investigate Small Aperture Radial Waveguide Slot Array
Antenna Design for Wireless Local Area Network Application [33], the design
worked at 2.4 GHz, This project will further the previous work by analyzing their
linearity polarized small aperture RWSA at 2.4GHz band and from their design and
develop a small aperture linearly polarized RWSA antenna based on IEEE 802.11b/g
standard to be high directivity and more functional for indoor WLAN applications.
28
2.12
Summery
The WLAN standard and requirements, characteristics of the RWSA antenna
and small aperture RWSA antenna studied and reviewed in this chapter. And
Parameter study of various antenna mechanical parameters is discussed Discussion
on level of influence of each mechanical parameter on return loss characteristic is
also presented, by focused on the high gain application.
Based on the literature review, the design specifications had been assigned
for the linear polarized small aperture RWSA antenna for this research project. The
design specifications include:
1. Frequency of operation lower UNNI ISM band 2.4GHz.
2. Antenna gain not exceeding 9 dBi.
3. Antenna type: Radial Waveguide Slot Array (RWSA).
4. Linear polarization.
CHAPTER III
RWSA ANTENNA DESIGN AND SIMULATION MODELLING
3.1
Introduction
Recent developments in Broadband application have increased the requires
for wide beamwidth of radiation pattern and lower antenna gain in contrast to other
high gain application like DBS, designing antenna may work on different situations.
Therefore only few slots are needed and hence produce a much smaller size compare
to the conventional RWSA antenna. The smaller size RWSA antenna also makes it
easier to fabricate and commercialized due to its low profile and low cost features.
Some of the obvious advantages of the small aperture RWSA antenna that
lead to the study of applying this antenna in the indoor and outdoor WLAN
applications is:
1. Excellent cost.
2. Excellent performance ratio.
3. Flat; can be concealed.
4. Maintenance free.
5. Hardware and network reliability.
6. Aesthetically pleasing.
7. Potential to build the antenna into building infrastructure.
There fore this chapter details the design stages and simulation modeling for
the RWSA antenna.
30
.
3.2
Antenna Structure
Simple structure is one of the most advantage of RWSA which aimed to
design. Therefore many factors should be considered especially that contribute to the
radiation characteristic for the annular slot fed by a radial waveguide like waveguide
mode, arrangement of the discrete slots, and annular slot conductance.
Figure 3.1: R WSA antenna structure.
The R WSA antenna shown in Figure 3.1 consists of:
1. Two plates that were adhered to a dielectric material; they act as the radial
cavity waveguide.
2. Upper plate bears the radiating slots pattern and the rear plate in corporate
feed element at its center.
3. Both plates spaced within distance d apart, and filled with a dielectric
material of dielectric constant more than one to provide slow wave structure
in the waveguide and thus avoiding grating lobes in the radiation pattern [33].
4. Slots were arrayed so that their radiations were added in phase in the beam
direction.
5. Power fed at the centre by coaxial cable and transfer into a radially outward
traveling wave with a rotational symmetry to excite the slots.
31
6. An area of certain radius on the upper conducting plate was left without any
slot to let the axially symmetric traveling wave to stabilize when entering the
feeding structure.
The antenna is drafted of two radial waveguide made of copper plate of
0.15mm thickness with a dielectric material adhere between the two radial
waveguide, with Four slots on the upper plate. The four slots are concentrically
arrayed along as annular path with radius, ρ a to form a single ring RLSA antenna.
Four slots are used as it produces vertical linear polarization due to the insignificant
Eφ component [32]. Every slot is positioned at the quadrant and tangent of the
annulus as demonstrated in Figure 3.2.
The four slots are arc-spaced by 0.47 λ g that produce the slot radius, ρ a
of 0.3λ g , where: λg <
λo
. The overall of the antenna radius is ρ w , sum of ρ a and
εr
ρ sc . The length of the slot Ls is near to the half wavelength in the radial waveguide
at the desired frequency.
Figure 3.2: The radiating surface of the RLSA antenna is formed by 4
discrete slots arranged at tangent of the array radius.
32
The choice of dielectric material is either Teflon with relative permittivity,
ε r =2.1 or Polypropylene with relative permittivity, ε r =2.33 and support the radial
waveguide height, d, where d <
λg
2
. The SMA connector with a coaxial fed
monopole is used in the design for coaxial-to-radial line adapter, which excites the
radial waveguide at the centre. Using the SMA connector, the adapter is free to
change its probe length, Lp which provides a lot of flexibility to the design
procedures. This project use coaxial-to-radial line adapter to be shorted (Lp=d) Probe
as shown in Figure 3.4.
Figure 3.3: RLSA antenna structure shorted probe (lower layout).
Figure 3.4: Insertion of coaxial monopole SMA connector into the slotted radial
waveguide through the backing plate.
33
3.3
Initial Calculation Results
Based on the structure of small aperture linear polarized RLSA antenna in
Figure 3.2 and the theoretical equations on Farah's 5.2GHz prototype [32], initial
parameters are calculated for both Teflon and Polypropylene. Generally, the
2.4GHz prototype is bigger in physical size as expected due to the lower frequency
value that leads to a higher guided wavelength value which is the main parameters
for the antenna structure. Calculations are summarized below:
Table 3.1: Initial calculation results based on 5.2 GHz antenna prototype.
Parameter
1. Dielectric Permittivity,
Material
Teflon
Polypropylene
2.1
2.33
εr
2. Guided Wavelength,
λg
3. Radial Cavity
Thickness, b
λg =
λo
εr
λg =
λo
εr
λo =
c
fo
λo =
c
fo
λo =
3 × 108
2.4 × 10 9
λo =
3 × 108
2.4 × 10 9
λo = 0.125mm
λo = 125mm
ε r = 2.1
ε r = 2.33
λ g = 86.26mm
λ g = 81.89mm
b<
b<
4. Slot Array Radius, ρ a
λg
2
86.26
2
b<
b<
λg
2
81.89
2
b<43.23mm
b<40.945mm
b=43.00mm
b=40.00mm
ρ a = 0.3λ g
ρ a =0.3 λ g
ρ a = 0.3(86.26)
ρ a =0.3(81.89)
ρ a = 25.88mm
ρ a =24.567mm
34
5. Slot Circuit Distance,
ρ sc =0.4 λ g
ρ sc =0.4 λ g
ρ sc
ρ sc =0.4(86.26)
ρ sc =0.4(81.89)
ρ sc =34.50mm
ρ sc =32.756
ρ w = ρ a + ρ sc
ρ w = ρ a + ρ sc
ρ w = 25.88 + 34.50
ρ w = 24.567 + 32.756
ρ w = 60.38mm
ρ w = 57.323mm
Angular Spacing=0.47 λ g
Angular Spacing=0.47 λ g
Angular Spacing=0.47(86.26)
Angular Spacing=0.47(81.89
Angular Spacing=40.54mm
Angular Spacing=38.48mm
Ls=0.5 λo
Ls=0.5 λo
Ls=0.5(124.91)
Ls=0.5(124.91)
Ls=62.46mm
Ls=62.46mm
9. Slot Width, ws
ws=6.3mm
ws=6.3mm
10. Slot coupling,
β = sin θ
β = sin θ
β = sin θ
β = sin 90 0
β = sin 90 0
β =1
β =1
6. Waveguide Radius, ρ w
7. Angular Spacing
8. Slot Length, Ls
Calculations based on the theoretical study of the 5.2GHz prototype for .the
2.4GHz design are not very practical and applicable. Even though it is not
uncommon that the design parameters are not interchangeable since both designs
are operating a different frequency. While the general concept can be adopted,
modifications on the design parameters are necessary to design for 2.4GHz RWSA
antenna.
The RWSA antenna with a radial cavity thickness of 40mm or more is not
practical and very costly to fabricate. Since the radial cavity thickness should be less
than half of the guided wavelength, the thickness will be fixed at 5mm for
practicality and cost effectiveness. The slot array radius of ρa = 0.3λ g would not
table to accommodate the four slots which have a length of Ls = 0.5 λo without the
slots will overlap on each other. Modification need to be made that the slot array
radius should be at lest half of the guide wavelength ρ a = 0 . 3 λ
.
35
3.4
Finite Difference Time Domain (FDTD) Simulation
Understanding electromagnetics (EM) and appreciating its applications in
microwaves, RF and antennas require a generally higher level of abstraction than
most other topics encountered by undergraduate and graduate electrical engineering
students. The need to maintain project interest, in spite of the reputation of
microwave and RF design as a difficult and abstract subject, leads us to considering
using simulation software and scientific visualization to render the abstract EM
concepts into a more intuitive form.
In this research project, electromagnetic tool based on the finite difference
time domain (FDTD) method Zeland FIDELITY version 4.0 is used to model the
antenna structure. The finite difference time domain (FDTD) method of
electromagnetic calculation is widely used in a variety of electromagnetic radiation,
integration and scattering applications. Advantages of Zeland FIDELITY version
4.0 are summarized as below:
1. Easy to implement.
2. Final algebraic equation in time-marching style.
3. Less computational resources for large structure (compare to MoM
simulator) and strong curved structure (compare to FEM simulator).
4. Wideband result (MoM and FEM provide result in sweeping frequency).
5. Able to handle complicated dielectric structures.
6. Possible to analyze all parts of the antenna.
The following list the basic procedures for FDTD calculations:
1. Pre-processing.
o Establish computational domain, the space where the simulation will be
perform.
o Define the entire geometry parameters including time step, domain size, cell
size, absorbing boundary and source condition.
I. Geometry definition
o Draw the geometry in the software layout.
36
o Specify materials (free space, metal, dielectric, permeability, permittivity,
conductivity etc) for each cell within the defined computational domain.
¾ define cell size
o Define cell size of structure, each cell. Size is defined as ΔX , ΔY , ΔZ for x, y
and z direction respectively.
o Cell size must be much less than the smallest wave length (1/10 of wave
length or less).
¾ Total number of cells.
o The number of cells for FDTD simulation is the sum of free space boundary
cells.
II. Time step calculation
o A geometry is modeled time step by time step.
o Choice of the grid size, will determine the accuracy of the analysis.
o Will affect the stability.
o Must be small enough with at least a fraction of the minimum wavelength to
ensure an accurate result.
1
Δt ≤
1
1 1
v max
+ 2 2
2
Δx
Δy Δz
o Where
Vmax = maximum phase velocity of the signal in the problem
Δ x, Δ y, Δ z= space increments in the x, y and z direction respectively.
III. Excitation and source modeling
o Excitation of FAT A calculation involves of time-varying source pulse that may be
modulated or unmodulated.
o Gaussian shape is chosen as the envelope of the source.
IV. Absorbing Boundary Condition (ABC)
o Establish a boundary.
o ABC simulates the field sampling space extending to infinity by suppressing
reflection of the outer boundaries.
2. Time stepping
o This process is the primary computational feature of an FDTD method.
o During simulation, the source condition, E-field, H-field components at each
point within the computational domain and absorbing boundary conditions
37
are updated.
3. Post processing
o Final step of FDTD analysis.
o The simulation result is presented at desired time step specifically at a point
within the computational domain for both E and H fields.
The FDTD simulation is chosen for the modeling of the small aperture RLSA
antenna as it is able to evaluate all parts of the antenna.
3.5
Antenna Simulation Modeling
The electromagnetic simulation software adopted is Zeland’s, which is one of
the most popular commercial product of its kind and yields high accuracy analysis
and design of complicated microwave and RF printed circuits, antennas, high speed
digital circuits and other electronic components Zeland is an integrated full- wave
electromagnetic simulation and optimization package for the analysis and design of
3-D Microstrip antennas, microwave and millimeter-wave integrated circuits, and
high-speed printed circuit board. It has become the most versatile, easy to use,
efficient and accurate electromagnetic simulation tool.
The finite difference time domain (FDTD) method, Zeland FIDELITY
version 4.0 will be used in the antenna structure modeling. The initial parameters for
the designed antenna will be used for initial simulation. Once the initial simulation
result is obtained, next will proceed to the optimization of the parameters, and finally
redesign of the RWSA antenna will be carry out if necessary.
The analysis, space that consists the antenna and space boundaries are
quantized by Yee cells, which dependent on the size of the geometry. The antenna
geometry was meshed into cubical size of 0.5mm. Figure 3.5 shows the antenna and
space boundary in the simulation domain.
38
X
Z
Y
Figure 3.5: Simulation domain in 3D outline view, which shows the antenna
structure and the space boundaries.
In the Zeland simulation environment, the antenna geometry included the
slotted upper plate, a dielectric disk, lower plate with centre hole, coaxial monopole
and the coaxial port. The boundaries were spaced with 5 cells from the antenna in all x,
y, and z directions. These geometries were combined to form the antenna structure,
thus modeling a true 3D metallic structure in multiple dielectric layers in an open,
closed or periodic boundary.
Several
geometries
with
different
parameters
are
analyzed
numerically, which is based on the method of moments. A RWSA with 4 Symmetric
Slots and a circular shape offers the most promising radiation characteristics had
been designed based on the small aperture RLSA 5.2GHz antenna [32].
The sequence of the defined objects is important to form the antenna structure
correctly. The object list in Figure 3.6 is vital to define the RWSA geometry
structure in the simulation environment.
39
Figure 3.6: Object list to define the antenna structure.
The slotted upper plate comprised of 2D circular copper plate of zero
thickness, while the four rectangular slots are defined from four 2D polygons. The
slots coordinates are determined in the AutoCAD drawing and transferred to the3D
structure as documented in APPENDIX A. Each object has to have their dielectric
properties defined for its geometry.
A wire is used to define the dielectric cylinder. The SMA connector which
made of gold is defined as an enclosed coaxial port to reduce the simulation domain
and therefore the simulation speed. The antenna is excited with sine modulated
Gaussian pulse. PML absorbing boundary condition (ABC) is applied in' the
simulation to truncate the analysis region. Figure 3.7 show the RWSA structure in
3D view.
Similar simulation setup will be expected in Zeland as Farah's
prototype [32], however the antenna parameters like dimensions, number of mesh
cubes, plate thickness etc will be different. Once the antenna structure is defined,
the time stepping process is ready to simulate the antenna structure.
40
Figure 3.7: 3D view of the antenna structure, built in FIDELITY. The structure is
meshed into small rectangular cubes.
The design parameters, initial calculation results, simulation tool and the
antenna design modeling in the simulation environment for the small size linear
polarized RWSA antenna are presented.
Next stage is to start simulate the design parameters, and analyses on the
simulation result in order to obtain an optimum results for the antenna prototype
before fabrication process.
3.6
Antenna Design and Simulation Results
Two important stages are involved in the simulation procedure in designing
the linear polarized RWSA antenna, first is the slot pattern design for radiation
pattern synthesis and next is the input impedance optimization.
41
3.7
Simulation Results
Simulation is carried out in three organized stages. First of all, the material
selection for Teflon or Poly-propylene need to be determine before proceeding to the
feeding technique determination. Finally, once the material and the type of feeding
technique are selected; input impedance optimization is carried out to obtain the
desired results.
3.8
Radiation Pattern
The radiation pattern is more directivity than previous design [33]. The
simulation illustrated in Figure 3.8 and Figure 3.9 shows an omnidirectional
radiation. Pattern with the shape resembles a flower. The radiation pattern is
symmetric at the broadside axis and with a deep null at the broadside and small back
lobe. The peak directivity is 8.03214dBi. The simulation radiation pattern is suitable
for the indoor WLAN environment and the directivity value is within the FCC
regulation.
Figure 3.8: Radiation pattern of the 2.4GHz RWSA antenna design.
42
(a)
(b)
Figure 3.9: 2.4GHz RWSA Antenna Radiation Pattern viewing from (a) z plane and
(b) y plane.
Simulation showed that the design produce a semi-omnidirectional flower
like radiation pattern (Figure 3.8) with the beamwidth of more than 100 degree and
directivity of 8.03214dBi. This fits indoor WLAN applications which require a wide
beamwidth. The measurement has very good agreement with the simulation result in
terms of resonant frequency. This wide variation is due to the inaccuracy in the
simulation meshing when it comes to very small structure like the SMA probe.
3.9
Return loss Various Frequencies
The simulation result of Received Signal Strength Index (RSSI) measurement
was carried out on the RWSA 2.4 GHz antennas. This result revealed that the
antenna can be applied for the IEEE 801.1lb/g applications.
Return loss versus Frequency in case of Polypropylene as radial waveguide
cavity, depending on the Return Loss result next step will be implementing and
improve this result for indoor WLAN.
43
Figure 3.10: Return loss in case of polypropylene as radial waveguide cavity.
Return loss results:
1. band width is 2.4835 - 2.4 = 0.025 × 109 = 83.5 MHz = 3.68%.
2. Return Loss = -30 dB.
3. Return Frequency = 2.44 GHz.
3.10
Comparison between this Design and Previous Design [33]
In this design we followed same previous design steps and then change the
antenna diameters in order to achieve the best return loss.
Comparison between this design and previous design
10
RL (dB)
0
2.25
-10
2.3
2.35
2.4
2.45
2.5
2.55
2.6
2.65
Last Design
-20
Previous Design
-30
-40
-50
Frequency (GHz)
Figure 3.11: Comparison between this design and previous design [33].
44
3.11
Summary
The design parameters, initial calculation results, simulation tools and antenna
design modeling in the software environment have been presented, simulation
analysis was performed and the optimum result were obtained for 2.4GHz RWSA
antenna prototype.
Next steps are to fabricate the antenna based on optimum simulation results,
and finally performance measurement of the antenna prototype.
CHAPTER IV
FABRICATION AND MEASUREMENTS
4.1 Introduction
The previous chapter discussed the calculations and the main idea of
the design, then the simulation results are manifested extremely good result. That
result was for the simulation environment not for real case. The real antenna
performance may be effected y many factors such fabrication inaccuracy, parameter
negligence, etc.
RWSA prototype fabrication process is the axon of this chapter,
including fabrications, measurements, adjustments, and performance analysis, its
practical approach towards the theoretical design.
Evaluation of the design will be depending on basic antenna
characteristics like return loss, gain, radiation pattern, and received signal strength.
Eventually, performance comparison analysis and evaluation will be discussed.
4.2 Antenna Prototype
The antenna prototype fabrication procedure is divided into two maim
portions, which are the RWSA slotted radial waveguide and the feed probe. Both
structures are then combining to complete the RWSA prototype structure. Figure 4.1
46
illustrates the RWSA antenna prototype in side view with reference to the material
selections and physical mounting.
Figure 4.1: The R WSA antenna prototype structure.
The RWSA slotted radial waveguide consists of a slotted upper copper plate,
the rear copper plate the dielectric substrate (Polypropylene) and the copper plate
that surround the RWSA radial cavity circumference. The polypropylene radial
waveguide was fabricated by CNC machine while the centre hole in the radial cavity
is drilled by drilling machine to ensure its accuracy as it is very difficult to cut using
conventional cutting tools. The upper and lower copper plates as well as the side
copper plate that cover the circumference of the radial waveguide was cut from thin
copper plate with thickness of 0.l5 mm. The simple structure of the copper plates
enable them to be cut using metal cutters without needing to send to the
manufacturer. The three plates were properly aligned and adhered to the
polypropylene radial cavity using double sided tape.
The feed probe section involves two items, the SMA connector and the brass
backing plate. The probe of the SMA connector is first trimmed to the suitable length
for open feed probe. The brass backing plate has 4.0mm thickness and a centre hole
of 4.0mm. The dielectric coating with 4.0mm diameter is cut to 4.0mm of length to
fit the back brass plate. The feed probe is then inserted into the centre hole of the
backing plate until the flange is attached to it and is held in position with screws. The
brass backing plate should use conductive epoxy to adhere to the rear copper plate to
ensure proper grounding. However, at the time of fabrication, double sided tape was
used to attach the back plate to the back of the copper plate as the conductive epoxy
is not available.
47
The antenna prototype parameters based on the optimum Zeland (FDTD)
simulation are as follow:
1. Radial cavity thickness, b=50.0mm.
2. Slot array radius, ρ a = 0.54λg = 44.5mm .
3. short circuit distance, ρ sc = 0.33λg = 27 mm
4. Waveguide radius, ρ w = ρ a + ρ sc = 71.5mm .
5. Center hole, ρ c = 0.65mm .
= 70.0mm .
6. Slot length, l s
7. Slot width, ws=6.0 mm.
Table 1 shows the parameters measurement for both the simulation and the
actual prototype. From the Table, the parameters are 0.5 -1mm difference. The slot
length difference is caused by the inaccuracy in the' cutting process. The centre hole
drilled by drilling machine is difference of 0.05mm. The negligence of the double
sided tape in the simulation causes difference in antenna diameter and the radial
waveguide height in the prototype. The brass backing plate is also neglected in the
simulation environment.
Table 4.1: antenna parameters comparison for simulation and prototype for First
design.
Antenna Parameters
Simulation (mm)
Prototype (mm)
Center hole diameter
1.8
2.0
Coaxial monopole length
4.8
4.8
Slot length
70.0
69.0
Slot width
6.0
7.0
Slot array radius
45.0
45.0
Antenna diameter
144.0
144.0
Dielectric height
5.0
5.0
Radial waveguide height
5.0
5.5
48
4.3 Antenna Measurement Setup
The measurement of return loss versus frequency for RWSA antenna
prototype was performed using S11 parameter. The setup of the measurement is
demonstrated by utilizing an Agilent 8722ES vector network analyzer [APPENDIX
B], the antenna radiating surface is aimed at free space or microwave absorbing
material during measurement.
4.4 Return Loss Measurement Result for the First Design
Figure 4.2 shows that the first design of RWSA antenna resonance at
frequency 2.5GHz giving a return loss of -28.323dB. The bandwidth is calculated
giving a result of 30MHz or 1.202%.
Return Loss Measurments for The First design
Return Loss (dB)
0
2.38
-5
2.4
2.42
2.44
2.46
2.48
2.5
2.52
2.54
-10
-15
First Design
-20
-25
-30
-35
Frequency (GHz)
Figure 4.2: Return loss result for R WSA first design antenna prototype.
It is apparent from Table above that very narrow bandwidth, there was no
increase of Return Loss associated with 2.4 GHz, No significant differences were
found between first design and simulations result. Overall, first design did not affect
differently in these measure.
49
4.5 RWSA 2.4 GHz Simulations and Prototype (First Design) Measurement
Comparison
Table 2: RWSA 2.4 GHz simulation and prototype measurement comparison
Parameters
Zeland simulation
Prototype measurement
2.4275GHz
2.5GHz
Return loss
-30dB
-28.323dB
Bandwidth
25MHz
30Mhz
Resonant frequency
4.6 Second Design
4.6.1 Introduction
It is becoming increasingly difficult to ignore the instability of the first design
which we already done, and there is a glitch resident in the frequency shifting.
However, the major problem with this kind of application is the IEEE802.11b/g have
specific frequency can operate. Therefore, there has been little discussion about
prefabricate the antenna with more abiding design, While a variety of definitions of
the term mismatching have been suggested [35].
4.6.2 Theoretical Ideas and Solutions
However, far too little attention has been paid to the effecting of the slots
dimensions on the Return loss measurements. The theoretical slot-design procedure
is similar to that proposed in [33], which concerned a double-layer RLSA with an
inward traveling radial wave. The discussed slot geometry resides on a single-layered
50
cavity. A unit radiator is defined as an adjacent slot pair lying along the Φ=constant
direction. With suitably chosen guide height (d< λg/2), the inner field is assumed to
be represented by a TEM wave whose variation with cavity radius is approximated
by
F ( ρ )αe
jK gp
4.1
For a given slot, the coupled field is proportional to the slot orientation factor
as given by:
g =e
jk g p
sin θ
4.2
Where θ is the angle the slot makes with the current flow line for the
resultant radiation from each slot to combine at bore sight to produce linear
polarization, the slot excitation phases are required to differ by 00 or 1800.
Therefore, the slot spacing is chosen as being half the guide. The semi-structured
approach was chosen because the evidence from this study suggests that increase the
length and decrease the width of the slots can reduce the frequency of the slot array
antenna. There is, therefore, a definite need for new particular design solves the
frequency shifting problems.
Another problem with the first approach was that it fails to take stable
matching position into return loss measurements operation, so we trend to reduce the
center hole diameter to be exactly like what we done in the simulation part, and we
used Epoxy adhered material instead of double sided tape, and the reason was to
reach the best grounded condition.
4.6.3 Second Design Structure
Table 3 shows the parameters measurement for both the simulation and the
actual prototype.
51
Table 3: antenna parameters comparison for simulation and prototype.
Antenna Parameters
Simulation (mm)
Prototype (mm)
Center hole diameter
1.8
1.8
Coaxial monopole length
4.8
4.8
Slot length
70.0
71.0
Slot width
6.0
6.0
Slot array radius
45.0
44.0
Antenna diameter
144.0
143.0
Dielectric height
5.0
5.0
Radial waveguide height
5.0
5.5
4.6.4 Comparison between the 1st & 2nd Design
Table below shows the technical differences between the 1st & 2nd design
Table 4: antenna parameters comparison for 1st & 2nd design prototype.
Antenna Parameters
First design
Second design
Center hole diameter
2.0
1.8
Coaxial monopole length
4.8
4.8
Slot length
69.0
71.0
Slot width
7.0
6.0
Slot array radius
45.0
44.0
Antenna diameter
144.0
143.0
Dielectric height
5.0
5.0
Radial waveguide height 5.5
5.5
(dielectric + double-sided
tape + copper plate).
It is apparent from this Table that very few different have been changed in a matter
to reach batter performance more stable and high band width.
52
4.6.5 Return Loss Measurement Result for the second Design
Figure 4.3 indicated that the R WSA antenna resonance at frequency 2.44GHz
giving a return loss of -30.3dB. The bandwidth is calculated giving a result of
83.5MHz or 3.68%.
Return Loss Measurments for The second design
Return Loss (dB)
0
-52.38
2.4
2.42
2.44
2.46
2.48
2.5
2.52
2.54
-10
-15
-20
Second Design
-25
-30
-35
-40
-45
Frequency (GHz)
Figure 4.3: Return loss result for R WSA second design antenna prototype.
Simple statistical analysis was used to reach the present result by depending on
the rabid change of SMA matching, through current satisfy result we can go
regresses the radiation pattern for only second design.
4.6.6 Comparison between the First and the Second Design Parameters
comparison
Return Loss (dB)
0
-52.38
Comparison Between the First and the Second Design
2.4
2.42
2.44
2.46
2.48
2.5
2.52
2.54
-10
-15
-20
Second Design
-25
First Design
-30
-35
-40
-45
Frequency (GHz)
Figure 4.4: Comparison between the First and the Second design Parameters.
53
From the data in Figure 4.4, it is apparent that the length of frequency during 2nd
design can be more useful for our applications. It can be seen from the data in Figure
4.4 and Figure 4.5 that the second design graph reported significantly more
contiguity to simulation results than the first design group.
4.6.7 Comparison between the RWSA Second Design and the Simulation
Results Biases on the Return Loss
Return Loss (dB)
Comparison between the Second design and the simulation
results
0
2.35
-10
2.4
-20
2.45
2.5
S
2.55
Second Design
Simulation Results
-30
-40
-50
Frequency (GHz)
Figure 4.5: Return loss result Comparison between the second design and the
simulation results.
4.6.8 RWSA 2.4 GHz Simulations and Prototype (Second Design) Measurement
Comparison
Table 5: RWSA 2.4 GHz simulation and prototype measurement comparison.
Parameters
Resonant frequency
Return loss
Bandwidth
Zeland simulation
2.438GHz
-30dB
45MHz
Prototype measurement
2.44GHz
-30.3dB
45Mhz
Strong evidence of 2nd design effectiveness was found when we compared the
result with the simulations, a positive correlation it can be used forward to apply the
antenna in the next level measurements.
54
4.7 Radiation Pattern Measurements
Figure below illustrate the direction of E-field, and the direction of H- field
for the single slot, since that Electrical and magnetic field are perpendicular on each
other, and the RWSA is circular shape, so the Electrical field pattern should be same
like Magnetic field pattern.
Figure 4.6: direction of E-field, and the direction of H- field for the single slot.
Figure 4.7 shows the 0o, 45o, and 90o which considered during the Radiation
pattern measurements in order to prove that the symmetric arrange of slots produce
E-field correspondingly to M-field.
Figure 4.7: Rotating degree during the Radiation field pattern measurements at 00,
45o, and 90o.
55
Figure 4.8: Radiation Pattern at 00.
Figure 4.9: Radiation Pattern at 450.
56
Figure 4.10: Radiation Pattern at 900.
Figures above may give us good results, since the pattern is directed in on
direction, which is close to what we have in the simulation results (see Figure 3.9.b).
There was some problem in the measurements during the Back loops, P18 anechoic
chamber ( place of Radiation pattern measurements) was not sealed environment, the
RF absorption and isolation capabilities is wanting, interference enter throw the
signal reflections from the open sides, Reflections in undamped screened rooms
significantly increase measurement uncertainty, and Poor grounding conditions. All
these reasons may have bad effecting on the measurements accuracy.
4.8 RWSA Antenna Gain Result over Deferent Frequencies
The gain was measured by applying RWSA antenna under different
frequencies, through Figure 4.11 it was -23 dBm, which equal to 7 dB, and it’s so
close to the directivity result (Figure 3.8), since the directivity was 8.03214dB so
there should wasted power because:
57
Gain = directivity × efficiency (η )
η = (Power output/ (Power output +Power Loss)
So, -23 dBm was quite good result.
RWSA Gain
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
-10
power (dbm)
-20
-30
RWSA
-40
-50
-60
-70
fre que ncy (GHz)
Figure 4.11: antenna gain under different frequencies.
It’s also possible to proof the Gain by calculating the antenna dimensions
⎛ N .Slotspacing ⎞
⎟⎟ dB,
Gain = 10 Log ⎜⎜
λ
o
⎝
⎠
⎛ 4 × 7.1 × 10 −2 × 0.6 × 10 −2
Gain =10 log ⎜⎜
3 × 10 8 / 2.4 × 10 9
⎝
4.3
⎞
⎟⎟ =-18.716 dB
⎠
By considering some power loss, it possible to assume this Gain is reasonable in
this case.
4.9 Received Signal Strength Index
Received signal strength index had been measured by using AirMagnet
software (see appendix C), Figure below shows that RWSA gives a higher RSSI
performance compare to the monopole antenna at the same measurement distance (5
58
and 22 meters) with the same frequency range of 2.4-2.4835 GHz.
RSSI Comparison between RWSA and Monopole on 5 meters
distance
-30
-35
0
2
4
6
8
10
12
dBm
-40
RWSA
-45
Monopole
-50
-55
-60
Channels
Figure 4.12: RSSI Comparison between RWSA antenna and RSSI of the
monopole antenna using AirMagnet for a short distance.
RSSI Comparison between RWSA and Monopole on 22 meters
distance
-66
-68 0
2
4
6
8
10
12
-70
d Bm
-72
RWSA
-74
Monopole
-76
-78
-80
-82
Cannels
Figure 4.13: Comparison between the RSSI of the RWSA antenna and RSSI of
the monopole antenna using AirMagnet for a Long distance.
59
4.10 Summary
Radial Waveguide Slot array antenna was successfully fabricated and the
return loss, Radiation pattern, gain, and received signal strength were measured and
performed. There was good agreement between simulation and prototype
measurements.
Receive signal strength results reveals that the 2,4GHz RWSA antenna
prototype has a better transmission quality than the monopole antenna in case that
radiation should be in one direction. So, RWSA antenna can operate in 2.4 GHz for
WLAN indoor environment.
CHAPTER V
CONCLUSION AND SUGGESTIONS FOR FUTURE WORK
5.1 Conclusion
This thesis has been concerned with successfully design, develop, and
fabricate RWSA, many publications discussed the large aperture design of RWSA
antenna, but only few who Dissect the small aperture of RWSA. Furthermore, the
small aperture RWSA antenna modeling is different from the large aperture case,
since the modeling of the later has ignored the cylindrical sort wall at the aperture
periphery and assumed for an infinite parallel plate.
The mentioned approaches are not suitable when design the small RWSA,
which antenna impedance need to be evaluated. The method of the moment has been
proposed to analyze the antenna performance in case of Return Loss, radiation
pattern, gain, and RSSI measurements.
The first stage of this project dealt with a monograph about the indoor
wireless local area network requirements, standards, and applications. The research
has taken an effort to learn the RWSA antenna characteristics. However, that was
important to elaborate exactly what happen during the radiating operation.
Next step, slot aperture that was used as the antenna radiator was
investigated. The information was important during the calculation part in order to
put the slot element at the right place on the radial waveguide.
61
There fore, the antenna design was analyzed using an FDTD based antenna
simulator, Zeland Fidelity 4.0. On account of the rectangular meshing of FDTD
method and the circular structure of the antenna design, the resolution was
maximized as high as 0.1mm to increase the accuracy.
Next step was optimizing the antenna parameters to obtain a good return loss,
and radiation pattern within the operation frequency, in reviewing the literature, no
data was found on the association between the best SMA position and antenna, when
we try to determine the most effective measurements we couldn’t put the SMA
screws exactly into the holes. So, we used for that tape to adhered the SMA with the
brass for the 2nd design. Measurements show agreement between the simulation
results and the prototype measurements in the term of the performance especially for
the second design.
The prototype was applied to the conventional WLAN access point and tested
for its network performance in terms of the received signal strength index. Result
indicate that the prototype cover the range for WLAN with a better efficiency than
monopole antenna.
RWSA antenna for indoor WLAN application for 2.4 GHz was successfully
design developed and proven in term of functionality, therefore it may considered as
another alternative for the monopole antenna.
5.2 Suggestions for Future Work
In order to design an antenna with higher directivity for outdoor WLAN in
2.4 GHz required to use in wireless campus project UTM so the future work will be
Simulate same antenna dimensions using Double-sided cupper clad board which
Consists of double-sided copper clad material with top and bottom cover films. The
cover films are pre-routed to access copper from both sides using plated thru holes
there are many benefits among this design idea like there upper and lower plate will
62
be very thin as we considered in the simulation part even slot etching will be easier.
But, there will be a big challenge waylays in the idea about drilling for inserting the
SMA wire inside the dielectric material, and how the absorbing material will be
surrounding the antenna.
Second proposal is optimizing of RWSA design. RWSA with good
performance from the point of view of gain, bandwidth, beamwidth, etc., can be
designed by optimizing its geometry. If the optimization is made by controlling scale
factor, spacing factor, subtended angle, zero offset, etc., higher gain, wider
polarization, bandwidth are likely to be achieved. These data must be interpreted
with caution because it still can reach the best, but meantime for this stage already
finished.
Different Slot antennas shape. The conventional RWSA shape determines the
shape of the uni-ominidirectional investigated here, but the slot antenna can be used
to create different overall geometries as well. We can be wound into a tapered
RWSA antenna (by using advanced design may allow us to increase and decrease the
entourage), or any other number of designs. The tapered RWSA antenna is expected
to offer wider bandwidths and it will be useful for many applications.
REFERENCES
1. T. E. Tice.; J. D. Kraus., The influence of conductor size on the properties of
helical beam antennas. Proc. Inst. Elec. Eng., November 1949, p. 1296.
2. V. H.. Rumsey., Frequency Independent Antennas. IRE national convention
record, Part I, pp. 114-118, 1957.
3. K.M. Luk.; K.W. Leung., Editors, Dielectric Resonator Antennas. Research
Studies Press Limited, Hertfordshire, England, UK, 2002.
4. Kin-Lu
Wong;
Fu-Ren
Hsiao;
Chia-Lun
Tang.
A
Low-Profile
Omnidirectional Circularly Polarized Antenna for WLAN Access Point.
Antennas and Propagation Society Symposium, 2004. IEEE. Vol. 3. 20-25
June 2004. pp. 2580 – 2583.
5. Jui-Hung Yeh; Jyh-Cheng Chen; Chi-Chen Lee. WLAN standards. IEEE
Potentials, Vol. 22, Issue 4, Oct-Nov 2003 pp. 16 – 22.
6. J. Weatherall.; A. Jones., Ubiquitous networks and their applications. IEEE
Wireless Commun., vol. 9, no. 1, pp. 18–29, Feb. 2002.
7. D. Remondo.; I..G. Niemegeers., Ad hoc networking in future wireless
communications. Comput. Commun. vol. 26, no. 1, pp. 36–40, Jan. 2003.
8. M. Kamenetsky. ; M. Unbehaun.., Coverage planning for outdoor wireless
LAN systems. In Proc. 2002 Int. Zurich Semin. Broadband Commun.–
Access, ransmission, Networking, Feb. 2002, pp. 49-1–49-6.
9. E. Amaldi.; A. Capone.; M. Cesana.; F. Malucelli., Optimizing WLAN radio
coverage. In Proc. 2004 IEEE Int. Conf. Commun., Jun. 2004, pp. 180–184.
10. C. Rensing.; M. Karsten.; B. Stiller. AAA: a survey and a policybased
architecture and framework. IEEE Network, vol. 16, no. 6, pp. 22–27,
Nov./Dec. 2002.
11. R. He, M. Yuan, J. Hu, H. Zhang, Z. Kan, and J. Ma, A novel serviceoriented
AAA architecture. In Proc. 14th IEEE Int. Symp. Personal, Indoor and
Mobile Radio Commun., vol. 3, Sept. 2003, pp. 2833–2837.
64
12. T. Braun and H. Kim, Efficient authentication and authorization of mobile
users based on peer-to-peer network mechanisms. In Proc. 38th Annu. Hawaii
Int. Conf. System Sciences, Jan. 2005, pp. 306b–306b.
13. K.C. Kelly., Recent Annular Slot Array Experiments. IRE National
Convection Records, vol. 5, pp. 144-151, March 1957.
14. Goebels, F. J. Jr. and Kelly, K. C. Arbitrary Polarization from Annular Slot
Planar Antennas. IRE Trans. Antennas Propag., AP-9, 342, 1961.
15. Kelly, K. C. and Goebels, F. J. Jr, Annular Slot Monopulse Antenna Arrays,
IEEE Trans. Antennas Propag., AP-12, 391, 1964.
16. Goto, N. and Yamamoto, M. Circularly polarization Radial Line Slot
Antennas. IECE Japan Technical Report. Aug 1980. AP80-57.
17. Sasazawa, H., Oshima, Y., Sakurai, K., Ando, M., Goto, N. Slot Coupling in
a Radial Line Slot Antenna for 12GHz and satellite TV reception. IEEE
Trans. On Antennas and Propagations. Sept. 1988. Vol AP-36. PP. 12211226.
18. Ando, M.; Skurai, K.; Goto, N. Characteristics of a Radial Line Slot Antenna
for 12GHz Bad Satellite TV Reception. IEEE Transactions on Antenna and
Propagation [legacy, pre -1988]. Vol. 34. Issue: 10. Oct 1986. pp.1269-1272.
19. Goto, N. and Yamamoto, M. Circularly Polarized Radial Line Slot Antennas,
IECE Techn. Rep. (in Japanese), AP80-57, 43, August 1980.
20. Takahashi, M. et al. A Single-Layered Radial Line Slot Antenna, IECE
Techn. Rep., AP89-54, October 1989.
21. Ando, M. et al. A Radial Line Slot Antenna for 12GHz Satellite TV
Reception, IEEE Trans. Antennas Propag., AP-33, 1347, 1985.
22. Ando, M. New DBS Receiver Antennas, Proc. 23rd European Microwave
Conf., Madrid, Spain, 1993,84.
23. Takahashi, M. et al. A Slot Design for Uniform Aperture Field Distribution in
Single-Layered Radial Line Slot Antennas, IEEE Trans. Antennas Propag.,
39, 954, 1991.
24. Davis, P.W. and Bialkowski, M.E. Linearly Polarised Radial Slot Antennas
with Improved Return Loss Performance, IEEE Antennas Propag. Mag., 41,
52, 1999.
25. Takada, J., Ando, M., and Goto, N. A Beam-Tilted Linearly-Polarized Radial
Line Slot Antenna, Electron. Commun. Jpn., 72, 27, 1989.
65
26. M. Ando.; T.Numuta., J. Takada.; N.Goto., A Linearly Polarized Radial Line
Slot Antenna. IEEE Trans. Ant. Propagat., vol. 36, pp. 1675-1680, December
1988.
27. S. Ramo.; J. Whinnery.; J. van Duzer., Fields and Waves in Communications
Electronics. J.Wiley ans Sons, New York, 1984.
28. R.A. Collin., Foundations of Microwave Engineering. McGraw-Hill, New
York, 1964.
29. J. Takada.; M. Ando.; N. Goto., Suppression of Reflection from Slots in a
Linearly-Polarized Radial Line Slot Antenna. Proc. of IEEE Ant. Propagat.
Int. Symp., pp. 1342-1345, 1991.
30. Takashi, M., Takada, J. Ando, M., Goto, N. Characteristics of Small
Aperture, Single-Layered, Radial Line Slot Antennas. IEE Pt. H. Feb 1992.
Vol 139(1). Pp. 79-83.
31. Zagriatski, S.; Bialkowski, M.E., Circularly Polarised Radial Line Slot Array
Antenna For Wireless LAN Access Point. 15th Int. conf. on Microwaves,
Radar and Wireless Communication, 2004. MIKON-2004. Vol. 2. 17-19 May
2004. pp.649 – 652.
32. Tharek, A. R.; Farah Ayu, I.K. Theoretical Investigations of Linearly
Polarized Radial Line Slot Array (RLSA) Antenna for Wireless LAN Indoor
Application at 5.5GHz. 11th Mediterranean Electrotechnical Conference,
2002. MELECON 2002. 7-9 May 2002. 7-9 May 2002.pp. 364 -367.
33. L.M. Choong., Small Aperture Radial Waveguide Slot Array Antenna Design
and Development for Wireless Local Area Network Application., University
Technology Malaysia, May 2006.
34. Robert G. Meyers; Qiubo Ye. Incorporation of Zeland’s IE3D in the
Microwave and RF Classroom. ECE Department, Rose-Hulman Institute of
Technology. Terre Haute, Indiana, US 47803.
35. Davis, P. W. and Bialkowski, M. E. Experimental Investigations into a
Linearly Polarized Radial Slot Antenna for DBS TV in Australia, IEEE
Trans. Antennas Propag., AP-45, 1123, 1997.
APPENDIX A
ANTENNA PROTOTYPE DIMENSIONS
68
Figure A.1 : 2.4 GHz antenna prototype.
68
Figure A.2 : 2.4 GHz antenna prototype side view.
68
Figure A.1 : 2.4 GHz antenna prototype tope view.
APPENDIX B
ANTENNA MEASUREMENT SETUP
B.1 Measurement of Return Loss versus frequency
The measurement of Return Loss versus frequency for RWSA antenna
prototype was performed using S11 parameter. The setup of the measurement is
demonstrated in figure B.1. The antenna radiating surface is aimed at free space or
microwave absorbing material during measurement.
TL Test Head
6583
Marconi Scalar Analyzer
6204
RF
RL
RLh
Out
RWSA
(AUT)
Figure B.1: Measurement setup for return loss.
APPENDIX C
RSSI SETUP
C.1 measurement of received signal strength index Versus WLAN
The measurement setup of RSSI for the monopole antenna and
2.4GHz RWSA antenna is illustrate in figure C.1. Measurement tools are
conventional WLAN access point (AP) with its antenna removable, a laptop with the
AirMagnet software. The measurements for 11 WLAN channels were taken for both
type of antenna using the same access point place at the same height and the same
distance from the access point with the same operating frequency.
Wall
Laptop with
AirMagnet software
A
P
d
Figure C.1: Measurement setup for RSSI
72
APPENDIX D
Matlab Code for Radiation Pattern Graphs
% Read data from the wanted file
fid=fopen('C:\Documents and Settings\LWAY\Desktop\matlab\faisal.dat','r');
a=fscanf(fid,'%f %f ',[2 inf]);
a=a';
status=fclose(fid);
angdeg=a(:,1);
dB=a(:,2);
angrad=angdeg*pi/180;
% limit the dB to a min of -40dB (as my PLOT package)
dBn = dB-min(dB);
%n=find(dBn<0);
%dBn(n)=zeros(size(n));
polar(angrad,dBn,'-r')
%text (-10,40,'0 dB');
%text (-10,30,'-10');
%text (-10,20,'-20');
%text (-10,10,'-30');
%text (-10,0,'-40');