DESIGN OF QUAD BAND ANTENNA FOR MOTOROLA TRANSCEIVER
SYSTEM
RUBINI VIJAYASURIAR
This project is submitted in partial fulfilment of the
requirements for the award of the degree of
Master of Engineering (Electrical-Electronic &Telecommunication)
Faculty Of Electrical Engineering
Universiti Teknologi Malaysia
NOVEMBER 2007
iii
My humble pranams at the lotus feet of Bhagawan
Specially dedicated to my beloved parents, family, and friends
who have always been there for me. Without their love and support,
none of this would be possible.
iv
ACKNOWLEDGEMENT
In preparing this thesis, I was in contact with many people, researchers,
academicians, and practitioners. They have contributed towards my understanding and
thoughts. In particular, I wish to express my sincere appreciation to my thesis supervisor,
Associate Professor Dr. Mazlina Esa for her invaluable guidance, critics, and motivation. I
would also like to thank Dr. Koh from Motorola technology for his guidance. Without
their support, this project would not have been completed successfully.
I would also like to acknowledge and express my gratitude to the following
people for their magnificent support and contributions to my journey of completing this
master’s programme.
For generously sharing their wisdom, support encouragement and patients. I would
like to extend my sincere appreciation to my fellow postgraduate classmates especially
Navindren, Ganavickenesh, Zul, and Chua who have provided assistance at various
occasions. Their views and tips were very useful indeed.
My precious friends for their love and support. Thank you Suresh for being there
thru good and bad times and whose love and support knows no limit. Hema, Kogi and
Easwari for their constant motivation and encouragement. And my amazing family: Mr.
Vijayasuriar my dad, my courageous and beautiful mother, Selvanayaky and my wonderful
sisters Shantini and Ghandini who have never fail to love, support and inspire me.
v
ABSTRACT
A rapid growth of personal communication has lead to the need for more
compact antennas. In addition, the increase in the capacity and quality of the new
services provided by mobile communications requires the development of new antennas
with wider bandwidths. At the same time, due to miniaturization of the transceivers, the
antennas should have small dimensions; low profile and the antennas should have the
possibility to be embedded in the terminals. This project involves the design of quadband antenna for a transceiver system of Motorola Penang. Available antennas are for
specific application and there is an immediate need to enhance these for quad-band
application. The operating frequencies of the antenna that will be looked into are the 800
Mhz/ 900Mhz, the GPS frequency of 1.5 GHz and 2.4GHz is WLAN s used for potential
dual mode iDEN-WLAN product Transmission line technology will be employed. The
operating frequencies will be controlled by different radiating structures of the proposed
antenna. Specific geometrical ratio of the individual segregated segment will be applied.
Hence, the frequency ratio of two adjacent resonant frequencies can be easily tuned to
the desired value of the wireless application. Simulations will be performed on the
designed antennas for good quad-band operation with low reflections. The work
involves simulations using SEMCADX simulation tool. This simulation tool is a 3-D
EM solver and is capable of representing data in time and in frequency domain .The
results obtained was analyzed.
vi
ABSTRAK
Peningkatan drastik kualiti dan kapasiti pelbagai servis baru dalam dunia
telekomunikasi, mewajibkan rekabentuk antenna baru yang bersaiz kecil dengan saluran
“bandwidth” yang lebih lebar. Dalam masa yang sama, disebabkan size transeiver yang
semakin kecil, rekabentuk antenna perlu mempunyai dimensi dan profil yang kecil untuk
dimuatkan dalam terminal.Projek in mendokumentasikan rekabentuk antenna “Operasi
Empat Frekuensi ” untuk sistem transeiver Motorola Penang. Antena sedia ada dalam
pasaran kini adalah untuk applikasi spesifik dengan frekuensi berasingan. Frekuensi
operasi antena yang akan direkabentuk ialah frekuensi GSM 800 MHz/900 MHz,
frekuensi GPS 1.5 GHz dan frekuensi WLAN 2.4 GHz.Teknologi talian transmisi akan
digunakan. Frekuensi operasi ini akan dikawal dengan struktur radiasi antena yang akan
direkabentuk untuk memudahkan applikasi tanpa talian specifik disambungkan. Simulasi
akan dibuat pada antena yang akan direkebentuk untuk ”Operasi Empat Frekuensi”
dengan nilai refleksi yang rendah. Kajian ini akan dibuat dengan alat simulasi
SEMCADX ialah alat simulasi 3D yang digunakan untuk penyelesaian elektomagnetik
serta boleh membuat representasian data dalam domain masa dan frekuensi. Hasil
simulasi telah dianalisi.
vii
TABLE OF CONTENTS
CHAPTER
1
2
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENTS
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
ix
LIST OF FIGURES
x
LIST OF SYMBOLS
xiii
LIST OF ABBREVIATIONS
xiv
LIST OF APPENDICES
xv
INTRODUCTION
1.1
Problem Statement
1
1.2
Overview of Antenna for Mobile Phones
3
1.3
Objective of project
4
1.4
Scope of project
5
1.5
Organization of Thesis
6
INTERNAL MOBILE ANTENNA TECHNOLOGY
2.1
Internal mobile antenna
8
2.2
Monopole Antenna
9
2.3
Antenna Parameter
11
viii
3
4
QUAD BAND ANTENNA DESIGN
3.1
Previous Work on Quad Band Antenna
16
3.2
Design consideration
21
ANALYSIS AND RESULTS
4.1
Individual arm simulation results
29
4.2
Further analysis on modified models
38
4.3
Optimum modified monopole
53
5
CONCLUSIONS
5.1 Conclusion
57
5.2 Future work
58
REFERENCE
59
Appendices
63
ix
LIST OF TABLE
TABLE NO.
TITLE
PAGE
1.1
List of frequencies and applications
9
3.1
Design flow of Quad Band antenna
26
4.1
Details of freq and BW
41
4.2
Overall performance of the ground
Plane length variation
4.3
46
Overall Antenna performance with
Additional plastic
51
x
LIST OF FIGURE
FIGURE
TITLE
PAGE
1.1
Multi antennas in a typical mobile environment
3
1.2
Current frequency bands used by mobile phones
4
2.1
Monopole Antenna
10
2.2
Radiation pattern for monopole antenna
11
2.3
Antenna VSWR Chart
13
2.4
Radiation pattern
14
2.5
Radiation pattern over a system coordinate
14
2.6
3D antenna radiation pattern
16
3.1
Layout of terminal antenna. All measurements in mm
17
3.2
U-Slot Patch
18
3.3
L-slot Patch
18
3.4(a)
Geometry of the proposed thin internal GSM/DCS
19
patch Antenna or a portable mobile terminal
3.4 (b)
Detailed dimensions of the top patch of the antenna
19
3.5
Geometrical configuration of the proposed antenna
20
3.6
Simulated geometry and parameter of the radiating
21
element
3.7
Design flow of quad band antenna
22
3.8
Final antenna configuration
23
3.9
3D Yee cell showing the E- and H-field
25
components in staggered grid
4.1
Monopole antenna 1, element 1 length =85mm
30
4.2
Monopole antenna 2, element 1 length =89mm
30
4.3
Monopole antenna 3, element 2 length = 30mm
30
4.4
Monopole antenna 4 , element 3 length = 50mm
31
xi
4.5
Frequency response for monopole antenna 1
32
4.6
Frequency response for monopole antenna 2
32
4.7
Results for monopole antenna 3
33
4.8
Results for monopole antenna 4
33
4.9
Monopole antenna 5
34
4.10
Monopole antenna 6
34
4.11
Monopole antenna 7
35
4.12
Results of monopole antenna 5
36
4.13
Results of monopole antenna 6
37
4.14
Results of monopole antenna 7
37
4.15
Results for final configuration with
39
element thickness varied
4.16
Upper mode BW Vs. Element Thickness
39
4.17
GPS mode Vs. Element thickness
40
4.18
Upper mode BW Vs. element thickness
40
4.19
Antenna element thickness Vs. Bandwidth
42
4.20
Overall antenna BW and S11 for different
43
ground plane size
4.21
Lower mode antenna BW and S11 for different
44
ground plane size
4.22
GPS mode antenna BW and S11 for different
44
ground plane size
4.23
Upper mode antenna BW and S11 for different
45
ground plane size
4.24
Bandwidth versus ground plane size for final
46
antenna configuration
4.25
S11 versus ground plane size for final antenna
47
4.26
Antenna configuration with additional plastic
48
4.27
Antenna performance with additional plastic with
49
various thickness
xii
4.28
Lower mode with additional plastic with various
49
thickness
4.29
GPS mode with additional plastic with various
50
thickness
4.30
Upper mode with additional plastic with various
50
thickness
4.31
Bandwidth versus plastic thickness
51
4.32
Return loss versus plastic thickness
52
4.33
Final antenna configuration with plastic
53
4.34
Final antenna element
54
4.35
Overall antenna design
54
4.36
Final antenna simulation results
55
4.37
Antenna efficiency for the upper band
55
4.38
Antenna efficiency for lower band
56
4.39
Antenna efficiency for GPS band
56
xiii
LIST OF SYMBOLS
Ω
- Ohm
%
- Percentage
eant
- Antenna total efficiency
eref
- Reference reflection (mismatch)
θ
- Radial distance in x-axia from x-y plane
Φ
- Radial distance in z-axis
η
- Efficiency
εr
- Dielectric constant
f
- Frequency
c
- Speed Of Light
λ
- Lambda
δ
-Loss Tangent
xiv
LIST OF ABBREVIATION
ABC
- Absorbing Boundary Condition
dB
- Decibel
EM
- Electromagnetic
FDMA
- Frequency division multiple access
FDTD
- Finite Difference Time Domain
GSM
- Global system for mobile communication
GPS
- Global Positioning System
IMTS
- Improved Mobile Telephone Service
ISM
- Industrial Scientific Medical
kHz
- Kilo Hertz
LCP
- Liquid Crystal Polymer
MHz
- Mega Hertz
NAMPS
- Narrowband Analog Mobile Phone Service
PCB
- Printed Circuit Board
PEC
- Perfect Electrical Conductor
PIFA
- Planar Inverted F Antenna
SRFT
- Simplifies Real frequency Technique
SAR
- Standard Absorption Rate
VSWR
- Voltage Standing Wave Ratio
WLAN
- Wireless Local Area Network
xv
LIST OF APPENDICS
APPENDIX
TITLE
PAGE
A
SEMCADX Feature and Option List
63
B
RT/Duroid Data Sheet
65
C
Element Thickness Results
67
D
Ground plane size Results
78
E
Plastic thickness Results
94
CHAPTER 1
INTRODUCTION
This chapter presents an introduction, which includes the problem statement,
background of the project, overview of mobile antennas, scopes and objective of the
project. The thesis outline is then given.
1.1
Problem Statement
In the past decade, cellular based communications have become a necessary
part of everyday life. Mobile communications are becoming increasingly integrated
into both terrestrial and satellite based radio systems with the impetus being personal
voice conversations [1]. The cellular infrastructure has developed and matured into a
reliable system that is utilized by many different types of communication systems.
Considerable effort has already been invested in developing the respective end-user
devices that work on the cellular system.
2
The development of cellular radio system has been rapid. Alongwith, demand
in the civilian use of terrestrial position-location systems has been rapidly increasing.
The civilian Global Positioning System, GPS, is quickly becoming the standard for
personal and commercial navigation and position location. The traditional
applications useful to professional navigators and surveyors have now permeating
the routine aspects of consumer life.
Existing consumer GPS applications are void of convenient method to
transmit the GPS determined position and velocity information to a remote location.
The GPS system of receive merely saw an obvious need to include transmit
capabilities over a wireless band to relay the data to a remote location. Many
different technological advances were introduced to facilitate the increased
appearance of personal communication devices; i.e., faster and more highly
integrated circuits, compact high-resolution display screens and lightweight powerful
batteries. These have experienced a similar reduction in size. The expansion of
wireless applications has also lead to an immediate need for reduced size multifunctional antennas that operate over broad bandwidths or multiple independent
bands.
With the increase in applications that operate at different frequencies, there is
a need for advanced antennas and antenna systems with new capabilities and better
performance. The use of multiple antennas adversely increases design complexity,
cost and size requirements, as shown in Figure 1.1 [2]. Therefore, there is a need for
a single multi-band operating antenna.
3
WiMax
IEEE802.15
WiFi
WLAN
Bluetooth
Cellular
GPS
3G
Figure 1.1: Multi antennas in a typical mobile environment [2].
1.2
Overview of Antenna for Mobile Phones
Antennas provide the transition between wireless communications interfacing
the free-space medium and the RF electronic of transceiver systems. The overall
perspective of wireless communication systems plus the pertinent details on the stateof-art aspects of associated technology show that, in modern deployment profile, the
manufacture of mobile phones antennas poses multidisciplinary considerations. The
characteristics of antennas used for mobile phones are as follows [3]:
i.
minimum occupied volume concerning portability and overall size
minimization of the mobile terminal and shape.
ii.
light weight
iii.
multi-band operation for different communication standard
iv.
adequate bandwidth covering the frequency range used by the system,
including a safety margin for production tolerances.
v.
good return loss, bandwidth, gain
and radiation pattern, operating
frequency and diversity
The design considerations have led antenna designers to consider a wide
variety of antenna structures to meet the often-conflicting needs for wireless
4
applications. To date, relatively small antennas have found acceptance in the rapidly
growing cellular phone market. Examples include monopole, loaded monopole, loop,
helical, Planar inverted-F antenna (PIFA), patch or slot type and multiple antennas
for diversity. Monopole antenna, is one of the latest antenna configurations [4]. It is
sensitive to dual polarization as well as possesses dual frequencies characteristics.
These make it even more appealing as one prime choice for growing
telecommunication industry. The antenna can be generally regarded as an omnidirectional, low gain and low profile antenna. It also uses the volume sharing
principle where, the longer arm can be used to resonate at a lower frequency band,
while the shorter arm can be used to resonate at a higher frequency band. Another
advantage of using monopole over other internal antennas is the ease of fabrication
and it has favorable electrical performance such as wide bandwidth. Figure 1.2
shows the current frequency bands used by mobile phones [5].
Figure 1.2: Current frequency bands used by mobile phones [5].
1.3
Objective of Project
The objective of this project is to design a quad band antenna that is suitable
for a transceiving system of Motorola Penang, Malaysia. The folded monopole
technology has been selected for the desired application.
5
1.4
Scopes of Project
The scopes of the project are as follows:
i.
Design single operating monopoles at four different bands i.e., 800
MHz and 900 MHz (mobile), 1.5 GHz (GPS), and 2.4 GHz (WLAN).
ii.
Simulate the single operating monopoles for comparison purposes.
iii.
Modify existing antenna to operate at quad band.
iv.
Simulate and perform parameteric investigations for optimum
performance using SEMCADX [6].
v.
Conclude the findings.
The proposed antenna is initially designed with individual arm to resonate at
the desired frequency Then, two arms are simulated together, followed by three arms
which can then operate as a quad band antenna. The final configuration is then
selected and further analysed by performing parameteric investigations of the ground
plane size, element thickness and adding plastic to the antenna. The designed
monopole antenna for Motorola Penang configurations are listed below:
•
Single Arm Monopole configuration
•
Double Arm Monopole configuration
•
Folded Arm Monopole configuration
•
J-Folded Arm Monopole configuration
•
Triple Arm Monopole Configuration
The design specification of the antenna is as follows:
(i)
operating frequencies of 890 MHz to 915 MHz, 935 MHz to 960
MHz, 1.575 GHz and 2.4 GHz
6
(ii)
voltage standing wave ratio, VSWR < 3
(iii)
good return loss of < -5 dB
(iv)
input impedance of 50 ohm
(v)
efficiency of > 60 %
The chosen microwave board has the following parameters:
(i)
microwave board
: RT/Duroid 5870
(ii)
thickness of substrate , h
: 1.6 mm
(iii)
relative permittivity of substrate, εr
: 2.33
(iv)
loss tangent of substrate, tan δ
: 0.0013
(iv)(v) thickness of conductor, t
1.5
: 35 µm
Organization of Thesis
This chapter presents an introduction, which includes the problem statement,
background of the project, overview of mobile antennas, scopes and objective of the
project. The thesis outline is then given.
In chapter 2, internal mobile antenna technologies are reviewed. This is
followed by brief discussion on the fundamentals of antennas.
Chapter 3 presents the undertaken design methodology. Numerical
simulations are described next.
7
Simulated results in the form of return loss response, voltage standing wave
ratio and radiation pattern are presented and discussed in Chapter 4. Optimizations in
the form of parameteric investigations are then carried out for optimum performance.
The final chapter concludes the thesis. Recommendations for future work are
also given.
CHAPTER 2
Internal Mobile Antenna Technology
2.1
Internal Mobile Antenna
Mobile terminals today are mostly equipped with the monopole antenna.
Monopoles are very simple in design yet are well suited to mobile communication
applications.
However, the linear monopole antenna possesses a number of drawbacks.
They are relatively large and protrude awkwardly from the handset case. The
problem with the monopole’s obstructive and space demanding structure also
complicate efforts taken to equip a handset with several antennas to enable multiband
operation. Monopoles also lack any built-in shielding mechanisms, to direct any
radiating waves away from a user body. Thus, this increases the potential risk of
producing cancerous tumors growth in the user’s head and also reduces the antenna
efficiency [6].
In recent years, the demand for compact handheld communication devices
has grown significantly. Antenna size is a major factor that limits device
9
miniaturization. The challenge in antenna designs calls for multiband capability,
apart from bandwidth enhancement. Multiband wireless phone has become popular
recently because they permit people to use the same phone in multi network that
have different frequencies. Table 1.1 lists a few useful wireless applications and their
operating frequencies. Systems that require multiband operation require antenna that
resonate at the specific frequencies. This only adds complexity to the antenna design
problem.
Table 1.1: List of frequencies and application [6]
Wireless Applications
GSM-900
GSM-1800
GSM-1900(USA)
3G-(UMTS2000)
2.2
Frequency Bands (MHz)
890 to 960
1710 to 1880
1850 to 1990
1885 to 2200
Monopole Antenna
The monopole antenna as shown in Figure 2.1 results from applying the
image theory to a dipole. If a conducting plane is placed below a single element of
length L/2 carrying a current, then the combination of the element and its image acts
identically to a dipole of length L except that the radiation occurs only in the space
above the plane [7]. The directivity is doubled and the radiation resistance is halved
when compared to the dipole. Thus, a half wave dipole can be approximated by a
quarter wave monopole (L/2 = λ/4). The monopole is very useful in mobile antennas
where the conducting plane can be the car body or the handset case. The typical gain
for the quarter wavelength monopole is 2 to 6 dB and it has a bandwidth of
approximately 10%. Its radiation resistance is 36.5 Ω and its directivity is 3.28 or
5.16 dB [8]. The radiation pattern for the monopole is shown in Figure 2.2.
10
In practical design, the quarterwave monopole does not require matching
circuits. The longer monopole induces less currents to the chassis of the phone, but
matching circuit is required.
Figure 2.1 : Monopole antenna [7]
Figure 2.2: Radiation patterns of a Monopole Antenna [8]
11
2.3
Antenna Parameters
Several important antenna parameters include Voltage Standing Wave Ratio,
VSWR, return loss or RL, directivity, gain, and efficiency.
(a)
VSWR and RL
VSWR and RL are used as performance parameters to quantify the
percentage of power that is reflected at the input to the antenna. VSWR closer to
1.0:1 is more desirable than one that is higher (i.e. 1.5:1 is better than 2.0:1).
Although a 2:1 VSWR implies a reflected voltage twice that of the forward voltage,
the actual power loss in radiation is 10 % or 0.5 dB. A VSWR of 3.0:1 is considered
the maximum acceptable and results in a 25% reduction of power or 1.2 dB loss.
Therefore, it is very important to attain the best impedance match possible for
maximum efficiency in the antenna system. Figure 2.3 shows a typical VSWR chart
where the band edges are at 2:1 VSWR and the center frequency of 2.45 GHz at 1:1.
RL refers to a measure of signal attenuation level as it is reflected from the
antenna. An open antenna has 0 dB return loss i.e. all the power transmitted to the
antenna is reflected. A near perfect match has an extremely large negative value
(typically -66 dB). A greater negative value is better than a smaller negative number
(i.e. – 20 dB is more efficient than –15 dB).
12
Figure 2.3: Antenna VSWR Chart [9]
(b)
Directivity and Gain
A critical factor when designing an antenna system is directing radiated
energy towards the receiver antenna. An isotropic source has radiated energy that is
spherical and provides equal intensity radiation in all directions. The gain is
determined by many factors such as type of antenna, electrical length, antenna
placement and antenna orientation. Gain and directivity can be controlled to a
certain extent. For instance, in some applications, it is beneficial to direct radiated
power towards the horizon for increased range.
One method to do this is by
changing the electrical length of an antenna so that the high angle of the radiation
component is redirected. Figure 2.4 shows a radiation pattern for a very directive
antenna.
13
Figure 2.4: Example of a Radiation pattern [10]
(c)
Efficiency
The quality of the transmission and reception of an antenna is strongly
dependent on the losses at the input terminals and within the structure of the antenna.
The total efficiency of an antenna has to take into account losses due to conduction
and dielectric properties of the antenna as well as losses caused by the reflections due
to mismatch between the transmission line and the antenna [10]. The total antenna
efficiency is computed as:
eant = eref .erad
(2.1)
where
eant ≅ total antenna efficiency
eref ≅ reflection (mismatch) efficiency = 1 − S11
2
erad = ec .ed ≅ conduction and dielectric efficiency ≅ antenna radiation efficiency
S11 is the Scattering parameter of input reflection coefficient.
For a diversity antenna system, the concept of efficiency has to be expanded
to include the effects of mutual coupling. This is defined as:
ediv = (eref .erad ) strongbranch .ecoupling
(2.2)
14
Due to decrease of mobile phone size, high efficiency antennas are difficult to
obtain. The total radiated power and sensitivity of the phones are not optimal, thus
network performance decreases. Standards to include the efficiency of mobile phone
antennas are under development both in Europe and the US. At 1800 MHz and
above, directive internal antennas can be used to decrease the power absorbed by the
user which may (or may not) cause problems for the behavior of the phone in the
network. Below 900 MHz, antennas of small handsets are not directive and difficult
to obtain high efficiency in talk position. Mean effective gain defines performance in
the network typically between 5 to 15 dBi.
(d)
Radiation Pattern
An antenna radiation pattern is the graphical representation of the radiation
properties of an antenna in its radiating far-field region. The same pattern holds for
the antenna operating in both the transmit and receive modes (i.e. reciprocity).
Radiation patterns are defined over a coordinate system, where r ≅ distance from
the origin , Φ ≅ radial distance (radians) from x-axis in x-y plane defined from 0 to
2π θ ≅ radial distance (radians) from the z-axis (downward is positive) defined 0 to π.
Figure 2.5: Radiation pattern over a system coordinate [11]
15
Three dimensionally, the radiation characteristics of the antenna/phone
system yields:
Figure 2.6: 3D antenna radiation pattern [11]
The relationship of gain and impedance to efficiency is
Rr
Rr + Rd
( 2.3)
G PK
Directivity
(2.4)
η=
η=
CHAPTER 3
QUAD-BAND ANTENNA DESIGN
This chapter reviews previous quad band antenna design available in the
literature. Design considerations for the proposed quad band antenna is then
presented. Brief description of the simulation software SEMCADX used is then
given.
3.1
Previous Work on Quad Band Antenna
The design and evaluation of a dual band PIFA antenna has been proposed
for the cellular bands GSM900/1800 (890 to 960 and 1710 to 1880 MHz) [12]. This
is shown in Figure 3.1. By applying a complex matching network, synthesized using
the Simplified Real Frequency Technique (SRFT) [13], the bandwidth of the antenna
has been extended for GSM850/900/1800/1900 coverage (824 to 960 and 1710 to
1990 MHz). Simulated and measured performances of a prototype antenna were
presented and discussed. A flat PIFA element is located in the topmost section 8 mm
above a typically sized 35×100 mm2 at the top-right positions for maximum
impedance bandwidth [14]. Dual-band functionality was implemented by using two
unequally sized galvanically coupled resonant patches [14]. A short patch is resonant
17
at 1800 MHz and a longer, bent patch, is resonant at 900 MHz, as indicated in Fig.
3.1. No substrate has been used for the PIFA carrier. The chassis is manufactured
using single-sided 0.8 mm FR-4 (εr = 4.44 and tan δ = 0.02) PCB, with the bottom
side metallized.
Figure 3.1: Layout of a terminal antenna. All measurements in mm [14]
A classical Planar Inverted-F (PIF) antenna was modified by etching plunged
in parallel U-slots of decreasing size, and by inserting a capacitive plate between the
radiating element and the ground plane [15]. The antenna was tuned by changing
positions and sizes of U-slots and the capacitive plate. An L-slot perturbation was
also investigated. By changing the dimensions of slots, the antennas were tuned for
operating in two frequency bands with the emphasis to the maximum width of the
frequency band (up to 80 % –10 dB return loss). The U-slot antenna is fed by the
microstrip line. Antenna dimensions are designed for the substrate CuClad 217
(dielectric constant εr = 2.17, substrate height h = 1.54 mm). Required operation
bands are around central frequencies f1 = 885 MHz, f2 = 1 875 MHz, and f3 = 2 460
18
MHz.. The L-slot antenna is fed by the microstrip line. Antenna dimensions are
depicted in Fig.3.2. The antenna is designed for the substrate FR4 (dielectric constant
is εr = = 4.17, substrate height h = 3.08 mm). Required operation bands are around
central frequencies f2 = 1 830 MHz and f3 = 2 430 MHz.
Figure 3.2: U-Slot Patch [15]
Figure 3.3: L-slot Patch [15]
19
A novel thin GSM/DCS dual-band internal patch antenna with an air-layer
substrate thickness of 3 mm only was designed [16]. The antenna has a simple
configuration as shown in Fig. 3.4. Two resonant modes at approximately 900 and
1800 MHz are easily excited by embedding a T-shaped slit in the antenna’s top
patch. By incorporating that, a small portion of the top patch is extended beyond the
top edge of the system ground plane of the mobile terminal, enhancing the
bandwidths of the two resonant modes for covering the GSM and DCS bands.
Figure 3.4 (a) Geometry of the proposed thin internal GSM/DCS patch antenna.
(b) Detailed dimensions of the top patch of the antenna [16].
The employed method of extending the antenna’s top patch over the top edge
of the ground plane is much simpler and more practical than employing slotted or
modified ground plane to improve the bandwidths of internal patch antennas [17],
[18]. The proposed antenna is especially suited for application in thin mobile phones
or PDA phones as an internal antenna.
20
Details of a capacitive coupled polymeric internal antenna for Bluetooth or
GPS application has been presented [19]. The proposed antenna assembly occupies
very little space on the PCB (as small as a 4 mm by 4 mm square on a varying
substrate height of 1 to 3 mm). The small element is a surface mount coupling plate
that can be manufactured and installed the same way present day chip antennas [19]
are manufactured and installed on wireless device PCBs. The actual radiating
element lies at a distance above it and is capacitively fed using the plate.
Since the radiating element is not on the PCB, it is not susceptible to
shielding cans or other metal objects nearby. The proposed radiating element can be
fabricated on a flexible film substrate such as liquid crystal polymer (LCP) from
Rogers Corporation and then adhesively bonded to the inside plastic cover of the
device. The absence of any physical connection with the actual radiating element
makes this design simple, easy, and cost-effective to manufacturers. Design
examples covering both the Bluetooth (2.4 to 2.485 GHz) and GPS (1.575 GHz)
frequencies are given.
The geometry of the proposed antenna is shown in Figures 3.5 and 3.6. There
are three metal layers. The first layer is the PCB of size 90 mm by 70 mm. The
coupling plate is located on the second layer. The actual antenna is on the third layer.
The complete structure in an actual usage scenario should be flipped upside down
with the antenna side on the top. The antenna is printed on an LCP film and then
adhesively bonded to the inside back cover of the device.
Figure 3.5 : Geometrical configuration of the proposed antenna [19]
21
Figure 3.6: Simulated geometry and parameter of the radiating element [19]
3.2
Design Considerations
A conventional monopole should be of quarter wavelength long, λ/4. Hence,
the corresponding lengths for each frequency of operation are as follows:
800/900 MHz band, λ/4 = 87.31 mm
1575 MHz band, λ/4 = 47.6 mm
2400 MHz band, λ/4 = 31 mm
There are several variable parameters available for parametric investigations. These
include feed location, element and ground plane length, height and width to achieve
optimization. In the thesis, the following parametric investigations were carried out:
i.
Element Length
ii.
Length of the ground plane
iii.
Dimensions of the plastic added to the antenna.
The first resonating element has an electrical length of 85 mm, where the first
two resonating frequencies are achieved with this single element. The first element
takes the shape of a C, and it was extended further to 89 mm, to achieve optimal
performance. The first antenna element is desired to achieve the first two resonating
frequencies in the mobile communication band, i.e., 880 to 960 MHz. Next, the
resonating antenna element was simulated with an electrical length of 30 mm to
achieve the 2.4 GHz WLAN band. The third element has a J-shape configuration and
22
was designed to have an electrical length of 50 mm to achieve the fourth resonating
frequency, 1.575 GHz the GPS frequency. The design of the quad band antenna is
achieved with individual arms resonating at the desired frequency. The single
elements are then combined and tuned to obtain the best result with least reflection
and a sufficient bandwidth. The final antenna element chosen was then further
analyzed. The antenna element thickness, ground plane size were varied. In addition,
a plastic holder to the antenna was added and the thickness of the plastic was varied.
The results obtained were analyzed. The overall design flow is summarized as Figure
3.7. Detailed investigation is given in chapter 4.
Start
Provide the first resonating
Element that resonates at the
first and second frequency
Provide the second resonating
Element that resonates at the
third frequency, which is
Jshape
Provide the third resonating
Element that resonates at the
fourth frequency
Results obtained are analyzed
Parametric analysis is done to
the antenna configuration.
Antenna Element is put
together and tuned to operate
at optimal resonating
frequencies
Figure 3.7: Design flow of Quad band antenna
The details of each antenna element used are explained in the next chapter,
together with the results obtained and analysis done on each model. Figure 3.8
shows an antenna configuration layout that was used for further parametric analysis.
23
Figure 3.8: Final antenna configuration
Various configurations were used in each step to achieve the desired
resonating frequencies. Among the configurations used are as below:
•
Single Arm Monopole configuration
•
Double Arm Monopole configuration
•
Folded Arm Monopole configuration
•
J-Folded Arm Monopole configuration
•
Triple Arm Monopole Configuration
The final configuration has a combination of the folded monopole that takes
the shape of “C”, a single linear monopole and also the J-folded arm monopole. This
means that they are integrated to obtain a single monopole antenna that operates at
quad band frequencies.
24
3.3
Brief Description of SEMCADX Simulation software
SEMCAD-X is a 3-D full wave simulation environment based on the FDTD
method, developed and provided by Schmid & Partner Engineering (SPEAG) [20].
The software is designed to address the electromagnetic TCAD needs of the wireless
and medical sectors in terms of antenna design, EMC and dosimetry. SEMCAD-X
provides standard RF solvers as well as Low Frequency solvers. Furthermore, a
range of specific method enhancements have been integrated. It allows rapid import
and processing of various CAD formats and features a uniquely fast OGL based
rendering engine. The postprocessor provides the extraction of any EM or SAR /
temperature related result. Finally, the direct combination of postprocessors for
SEMCAD-X and the DASY4 near-field scanners enable a direct comparison of
simulated and measured data. In addition, a multi-parameter multi-goal optimization
engine based on Genetic Algorithms allows to optimize CAD imported and derived
structures of any complexity.[6]
The steps involved in the simulation can be summarized in three simple steps
as below:
•
Modeling the Plane Antenna model
•
Entering the relevant simulation parameters, setting up the grid and voxeling
the model
•
Running the simulation and extracting the results
The simulation parameters that need to be set are frequency of operation,
bandwidth, selecting the boundary condition, source and exitation, assigning the
materials for each element in the simulation, and sensors that is needed to obtain far
field data.
The Finite-Difference Time-Domain method (FDTD) formulation is now
described.[6]
25
(a)
Discretization of Maxwell’s Equations
The FDTD is a direct solution of Maxwell’s curl equations in the time
domain [21]. The electric and magnetic field components are allocated in space on a
staggered mesh of a Cartesian coordinate system shown in Figure 3.9. The E and Hfield components are updated in a leap-frog scheme using the finite-difference form
of the curl which surrounds the component. The transient fields can be calculated
when the initial field, boundary and source conditions are known. Maxwell’s curl
equations are discretized using a 2nd order finite-difference approximation both in
space and in time in an equidistantly spaced mesh. The first partial space and time
derivatives lead to
∂F (i, j , k , n) F n (i + 1 / 2, j , k ) − F n (i − 1 / 2, j , k )
+ O[(∆x) 2 ]
=
∂x
∆x
(3.1)
∂F (i, j , k , n) F n +1 / 2 (i, j , k ) − F n−1 / 2 (i, j , k )
=
+ O[(∆t ) 2 ]
∂t
∆t
(3.2)
with F n as the electric (E) or magnetic (H) field at time n · ∆t , i, j and k are the
indices of the spatial lattice, and O[( ∆x )2] and O[( ∆t )2] are error terms.
Figure 3.9: 3D Yee cell showing the E- and H-field components in Staggered
grid.[16]
26
For the explicit finite-difference scheme to yield a stable solution, the time
step used for the updating must be limited according to the Courant-Friedrich-Levy
(CFL) criterion. For the FDTD formulation of Maxwell’s equations on a staggered
grid, this criterion reads
∆t ≤
1
1
1
1
+
+
c
2
2
(∆x)
(∆y )
(∆z ) 2
(3.3)
where ∆x, ∆y and ∆z are the mesh steps of a Cartesian coordinate system and c the
speed of light within the material of a cell.[6]
From Equation 3.3, it is clear that the time step is directly related to the cell
size.
The cell size therefore has a significant impact on the computational
requirements of a simulation. In an equidistantly spaced mesh, a reduction of the
mesh step size by a factor of two will increase the necessary storage space by a factor
of eight and the computation time by a factor of 16 (!). For nonuniform meshes, the
impact of the smallest mesh cell on storage space is not as high. Nevertheless, the
time step must be chosen for the smallest cell in the mesh. Therefore this affects the
overall simulation time as well.
As a powerful enhancement to reduce computational resources while
maintaining its accuracy, SEMCAD-X features a Conformal FDTD Solver. The
ability to use a conformal mesh with coarser spatial resolution than nonetheless
produces the same accuracy as a fine staircasing mesh results in remarkable savings
in memory requirements (fewer cells) and simulation time (larger time step).[6]
PEC (perfect electric conductor) model is used for all metals in the
simulation. In this algorithm the effective PEC-free edge length and the PEC-free
area are taken into account while time updating. Generally, the improvement in
27
accuracy is much more significant than for dielectric models. Furthermore, there is
no need to reduce the conventional time step in order to guarantee numerical
stability, i.e., the method is always stable. However the algorithm’s accuracy can be
improved with a slightly reduced time step. Therefore the user can put a specific
focus on either speed or accuracy. The time step reduction benefit can be dependent
on the example.[6]
(b)
Boundary Condition Used
The boundary condition used is the Analytical Absorbing Boundary
Condition. Theoretically, the transparent boundary condition is a non-local operator,
since for each point on the boundary the values therein relate with the values at all
points on the boundary. [6] Therefore, substituting the transparent boundary
condition by a local boundary condition, such as the analytical absorbing boundary
condition (A-ABC), is actually making a high frequency approximation. In other
words:
• the extent of the boundary must be large compared to the wavelength,
• the boundary must be put far away from large objects, and
• the efficiency is sensitive to the incident angle of the incoming wave.
CHAPTER 4
ANALYSIS AND RESULTS
This chapter presents all the simulated results obtained using SEMCADX.
The results are then analyzed and discussed.
4.1
Individual Arm Simulations
The monopole antenna was first designed individually to resonate at each
corresponding desired frequency of operation. The individual arm should resonate at
the individual 800/900 MHz, 1.5 GHz, and 2.4 GHz frequencies, as shown in Figures
4.1 and 4.4. Specifically, the desired operation bands are around central frequencies
f1 = 892.5 MHz and f2 = 947.5 MHz, f3= 1.575 GHz and f4 = 2.4 GHz.
The chosen RT/Duroid microwave laminate board has the following
parameters: dielectric constant, εr = 2.33, substrate thickness, h = 1 mm, substrate
loss tangent = 0.0013, thickness of Cu layer = 35 µm. The monopole has microstrip
line feed. Very low loss dielectric property is observed.
30
Figure 4.1 Monopole antenna 1, element 1 of length 85 mm
Figure 4.2: Monopole antenna 2, element 1 of length 89 mm
Figure 4.3: Monopole antenna 3, element 2 of length 30 mm
31
Figure 4.4: Monopole antenna 4, element 3 of length 50 mm
Each of the four Monopoles was simulated with a fixed ground plane size of
80 mm. The results obtained for individual arm are as shown in Figures 4.4 to 4.7.
All the monopoles are resonating well at their desired frequencies of operations with
reasonably good return loss of better than -12 dB. The respective return losses of the
Monopole 1, 2, 3 and 4 are -21 dB, -18 dB, -12 dB and -13 dB. It can be observed
that Monopole antenna 1 resonates at the second desired operating frequency, which
is f2 = 947.5 MHz, but does not cover the first operating frequency. Monopole
antenna 2 is the extension of monopole antenna 1. The results obtained showed that it
is able to resonate at the first two operating frequencies, i.e., f1 = 892.5 MHz and f2 =
947.5 MHz. However, the reflection bandwidth obtained exceeds the desired 50
MHz for both frequencies. Both monopole antennas 1 and 2 exhibit third resonance
at 3.0 GHz. This is also the harmonic of the first resonating frequency, respectively.
32
Figure 4.5: Return loss response of monopole antenna 1
Figure 4.6: Return loss response of monopole antenna
33
Figure 4.7: Return loss response of monopole antenna 3
Figure 4.8: Return loss response of monopole antenna 4
34
Monopole antennas 3 and 4 have been designed to operate at 2.4 GHz and
1.575 GHz, respectively. Both antennas show good results and the resonating
frequency corresponds to the λ⁄4 values.
The antenna configuration with two monopole arms was simulated, and the
resonance of the elements was analyzed. Figure 4.9 shows the Monopole antenna 5
that is a combination of Monopole antennas 1 and 3. The antenna was then
simulated. In Figures 4.10 and 4.11, all three antenna elements are combined forming
Monopole antennas 5 and 6. The coupling effects of individual arms require the
antenna to be further fine-tuned to achieve desired quad-band frequencies.
Figure 4.9: Monopole antenna 5
Figure 4.10: Monopole antenna 6
35
Figure 4.11: Monopole antenna 7
The simulated RL of Monopole antenna 5 is shown in Figure 4.12. It can be
inferred that the combination of Monopole antennas 1 and 3 provides resonances for
the first three desired operating frequencies. However, poor RL of merely -7.5 dB is
obtained at 1.575 GHz. This is due to a change in the input impedance, thus causing
impedance mismatch when more than one monopole antenna added together to the
desired 50 Ohm input of the antenna. The input impedance reduces causing slight
impedance mismatch. Nevertheless, this can be overcome by adjusting the feed
position for a better RL response that allows less reflection at the input, thus reducing
the impedance mismatch.
Monopole antenna 6 is the combination of Monopole antennas 1, 2 and 3. It
uses the J-folded arm to resonate at the GPS frequency, the extended C arm to
resonate at the mobile frequency, while the single linear arm is used to resonate at
the WLAN frequency. The configuration is able to resonate at all quad frequencies
but with relatively sufficient impedance match at the input.
Monopole antenna 7, on the other hand uses the J-folded arm to resonate at
the mobile frequency, and the extended C arm for the GPS frequency. The
configuration also resonates at all 4 frequencies, but the RL achieved do not meet the
desired design specification.
36
Figure 4.12: Return loss response of Monopole antenna 5
Figure 4.13: Return loss response of Monopole antenna 6
37
Figure 4.14: Return loss response of Monopole antenna 7
It can be inferred that the simulated results obtained showed that Monopole
antenna with individual arm resonates well at the desired frequency that corresponds
to the λ⁄4 length. Monopole antennas were tuned for operating in quad frequency
bands with the emphasis to the maximum width of the frequency band (up to 20 %
for the allowable return loss –6 dB) and efficiency of at least 60%. Monopole
antenna 6 configuration is the selected antenna configuration for further parametric
investigation.
38
4.2
Further Analysis of Modified Monopole
Further investigation was then performed on the Monopole antenna 6 for
parametric studies. The varying parameters are element thickness, ground plane size
and a plastic holder was added to the antenna with varying thickness. The simulation
results obtained was analyzed and the best parameters were selected.
(a)
Varying element thickness
The element thickness of the antenna was varied form 0.25 to 1 mm in steps
of 0.25 mm. The simulated results obtained are as shown in Figures 4.15 to 4.18.
Figure 4.15: Simulated RL of Monopole 6 with varying element thickness
39
Figure 4.16: Variation of Upper mode BW with Element Thickness
Figure 4.17: Variation of GPS mode BW with Element thickness
40
Figure 4.18: Variation of Upper mode BW with element thickness
The element thickness was varied from 0.2 mm to 1 mm. This was done in
order to help improve the antenna BW for all the operating modes; lower, GPS and
upper modes. It was found that the BW does not change significantly for each mode.
The best BW is obtained when element thickness is 1 mm.
Table 4.1: Frequency and BW Performances with Varying Element Thickness
41
Figure 4.19 shows the relationship of the operating bandwidth with element
thickness of Monopole Antenna 6. There is a slight increase in bandwidth for the
lower mode and the GPS mode as the antenna element becomes thicker. The upper
mode exhibits almost constant bandwidth.
This is because, when the antenna
element is thicken, the quality factor of the antenna decreases and the εr of the
antenna also decreases, thus the surface of the radiating element will be further away
from the ground plane and therefore it will increase the bandwidth [20]. In this
study, however, the change is not as significant as in reference [21], because the
change in element thickness is only up to 1 mm to ensure that the antenna is able to
fit into a compact mobile phone compared to the study done up to 3 mm that showed
a more significant change in the bandwidth of the antenna being studied.
Bandwidth (%)
Measured Impedance Bandwidth Vs. Element Thickness
40
35
30
25
20
15
10
5
0
Lower mode
GPS mode
Upper mode
0.25mm
0.5mm
0.75mm
1.0mm
Thicknes (mm)
Figure 4.19: Relationship of Bandwidth with Antenna element thickness.
(b)
Varying ground plane size
Based on reference [22], the size of the ground plane plays an important role
in widening the antenna’s bandwidth. The ground plane size was varied from 70 mm
to 100 mm (normal mobile phone size), and the results obtain is as above. Two
parameters were taken into consideration, the RL and the BW improvement seen for
42
the variation. Figures 4.20 to 4.23 show the detail analysis of the results obtained. It
can be seen that the lower mode (800/900) is achieved, while the best BW is
obtained at 90 mm ground plane size. For the GPS mode, the best ground plane size
is obtained at 75 mm and 80 mm, while for the upper mode the best BW is obtained
at 70 mm. The trend observed is that the upper and GPS band BW deteriorates, as the
length of the ground plane increases. The lower band has a reverse trend, where the
bandwidth improves as the ground plane size increases and, this remains constant
from 90 mm to 100 mm. The impedance bandwidth of the upper band could not be
obtained at 95 mm and 100 mm. Hence, an intermediate value needs to be taken to
get best bandwidth for all operating mode, which is ground plane length of 80 mm.
For the RL variations with length of the ground plane, it can be seen that the
lower mode achieves better impedance match RL as the length of the ground plane
increases. The GPS mode and the upper mode exhibit an opposite trend, where RL
decreases with the increase of the ground plane length. The best overall value for
both the BW and RL is 80 mm. This also is the best value based on the antenna
element thickness, and similar to the trend seen in reference [23] to [27]. The overall
performance is tabulated in Table 4.1.
43
Figure 4.20: RL and BW variations of Monopole antenna 6 for varying ground
plane sizes
Figure 4.21: Lower Mode RL and BW variations of Monopole antenna 6 for
varying ground plane sizes
44
Figure 4.22: GPS Mode RL and BW variations of Monopole antenna 6 for varying
ground plane sizes
Figure 4.23: Upper Mode RL and BW variations of Monopole antenna 6 for varying
ground plane sizes
45
The ground plane was varied and the BW and RL variations are shown in
Figures 4.24 and 4.25. the bandwidth of the antenna at the lower band increases as
the length of the ground plane increases. The trend seen for the GPS and the upper
band , the bandwidth of the antenna decreases until there is no change after it reaches
a length of 90mm, where at this point the ground plane acts like an infinite ground
plane. Lengthening the ground plane length affect the higher frequency where the
return loss and the bandwidth decrease because the λ length that is shorter [28].
Table 4.2: Overall performance of the Monopole antenna 6 with varying ground
plane length
BW (%)
Bandwidth Vs. Ground Plane Length
45
40
35
30
25
20
15
10
5
0
Lower mode
GPS mode
Upper mode
70mm
75mm
80mm
85mm
90mm
95mm
100mm
Length (mm)
Figure 4.24: BW relationship with ground plane size for Monopole antenna 6
47
S11 Vs. Length
0
-5
70mm
75mm
80mm
85mm
90mm
95mm
100mm
S11
-10
Lower mode
-15
GPS mode
-20
Upper Mode
-25
-30
-35
Length
Figure 4.25: RL relationship with ground plane size for Monopole antenna 6
(c)
Adding plastic
The plastic used within the handset may be chosen for their mechanical
properties and low cost rather than their dielectric and loss tangent parameters. Lossy
plastics are an obvious area of concern, but cost drivers mean that it is not normally
possible to use low loss plastics throughout the design.
In practical design of an antenna in mobile phone, The antenna will be
mounted to a plastic or bracket to hold the antenna in place. With this in
consideration, the antenna designed was placed on a plastic holder the same size as
the antenna area used. The plastic holder thickness was varied from 0.25 mm to 2
mm in steps of 0.25 mm. Figure 4.27 shows the BW and S11 variation with the
change in thickness of the plastic used. The BW for the upper mode does not change
with the variation in thickness. The best BW is seen at 1.0 mm for the GPS mode.
The lower mode, the best BW is obtained at 1.25 mm and 1.5 mm thickness.
48
Based on the return loss, for the lower mode, the best return loss is seen at 1
mm and 2 mm, for the GPS mode, the same trend is observed. The upper mode on
the other hand, does not change with the varied thickness of the plastic being used.
Taking both the BW and return loss into consideration, the best value for the
thickness of the plastic is 2mm, where a good return loss is seen for GPS and the
lower mode and at the same time, the percentage of BW for all three band are
approximately the best compared to other thickness used.
Figure 4.26: Antenna configuration with additional plastic
49
Figure 4.27: Antenna performance with additional plastic with various thickness
Figure 4.28: Lower mode with additional plastic with various thickness
50
Figure 4.29: GPS mode with additional plastic with various thicknesses
Figure 4.30: Upper mode with additional plastic with varying thickness
51
Table 4.3: Overall Antenna performance with add-on plastic
BW Vs. Plastic thickness
35
30
lower mode
20
GPS mode
15
Upper mode
10
5
2.
0m
m
m
1.
75
m
1.
5m
m
m
1.
25
m
1.
0m
m
m
0.
75
m
0.
5m
m
m
0
0.
25
m
BW (%)
25
Thickness of plastic (mm)
Figure 4.31: Bandwidth versus plastic thickness
52
S11 Vs. Plastic Thickness
0
0.25mm 0.5mm 0.75mm 1.0mm 1.25mm 1.5mm 1.75mm 2.0mm
R e tu r n L o s s
-5
Lowe Mode
-10
GPS Mode
-15
Upper Mode
-20
-25
Plastic Thickness (mm)
Figure 4.32: Return loss versus plastic thickness
Figure 4.32, shows the behavior of the bandwidth versus the plastic thickness
added to the antenna. As shown, the trend seen for the upper band is almost constant
bandwidth as the thickness of the plastic increases. The lower band on the other hand
experiences a decrease in bandwidth when plastic thickness varies from 0.25 mm to
1 mm. beyond that, there is an increase in bandwidth. The GPS band exhibits the
best bandwidth at 1 mm and 2 mm plastic thickness.
The plastic that is added to the antenna causes the permittivity of the
dielectric used to increase thus increases the Q factor of the antenna. The antenna
will not be further away from the ground plane. [28] The equation (4.1), show the
relationship between the bandwidth and the quality factor. Hence, the bandwidth will
decrease when Q factor increases. Such trend is observed when the bandwidth
decreases as the thickness of the plastic increases.
BW = ∆f =
fo
Q
(4.1)
53
Figure 4.32 shows the relationship of RL with varying plastic thickness.
Here again, the upper band remains but the lower and the GPS bands exhibit similar
trend. The best value of thickness that provides good RL for all three bands is the 1
mm plastic thickness. Considering both the BW and RL parameters, the 1 mm
thickness is selected.
4.3
Optimum Modified Monopole
The final antenna configuration was designed to have a ground plane size of
80 mm, a plastic thickness of 1 mm and element thickness of 1 mm. Figures 4.33 to
4.35 show the final antenna configuration that was designed. The final results
obtained is shown in Figure 4.36, where the antenna resonated well at all four desired
frequencies and exhibits sufficient RL of less then -6 dB.
Figure 4.33: Optimum modified monopole with plastic
54
Figure 4.34: Optimum modified monopole antenna element
Figure 4.35: Overall optimum modified monopole antenna
55
Figure 4.36: RL response of optimum modified monopole antenna
The antenna efficiency can be seen from Figures 4.36 to 4.38. The antenna is
able to meet efficiency of more than 60% for the useful desired frequency and meets
the design specification.
Efficiency
Upper band
90.00%
80.00%
70.00%
60.00%
50.00%
40.00%
30.00%
20.00%
10.00%
0.00%
Upper band
2.350
2.375
2.400
2.425
2.450
Frequency
Figure 4.37: Antenna efficiency for the upper band
56
Lower mode
120.00%
E ffi c i e n c y
100.00%
80.00%
60.00%
Lower mode
40.00%
20.00%
95
80
0. 9
65
0. 9
40
0. 9
25
0. 9
10
0. 9
95
0. 9
80
0. 8
65
0. 8
50
0. 8
35
0. 8
0. 8
0. 8
20
0.00%
Frequency
Figure4.38: Antenna efficiency for lower band
E ffi c i e n c y
GPS BAND
90.00%
80.00%
70.00%
60.00%
50.00%
40.00%
30.00%
20.00%
10.00%
0.00%
GPS BAND
1.500
1.525
1.550
1.575
1.600
Frequency
Figure 4.39: Antenna efficiency for GPS band
CHAPTER 5
CONCLUSIONS
This chapter summarizes the findings and suggests potential future work.
5.1 Conclusions
The main aim of this thesis is to design a quad band antenna for Motorola
transceiver system. A sound understanding of the principles in antenna design
and monopole antenna technology for mobile communication is studied. In order
to accomplish the aim of this thesis, four objectives are defined in chapter one of
this report. The primary aim is to obtain an optimal antenna design that meets all
the design specification. A practical antenna that has efficient, practical, and
small and low profile that is suitable to be integrated into Motorola handheld
device is selected. This was accomplished through an extensive research on
technical papers, journals, books. A careful study shows one of the most
promising antennas configuration suitable for integrating into modern handset
design is the monopole antenna technology.
58
Once the antenna has been determine, the next step is to ensure that the
selected antenna meets specification. Therefore, Specific geometrical ratio of
structure was identified and parameters was set for the antenna design.
Final antenna configuration was chosen and further parametric analysis was
done. Simulate and optimization of design was done using SEMCADX.
Simulation results were analyzed to ensure good resonance of low return loss was
obtained.
5.2 Future work
Possible future work for this project could include different bands and design
techniques can be used for future work. Miniaturizing the antenna for size
reduction of the final design can be looked into. Many techniques can be used
for this purpose including meanderizing the antenna.
Fabrication of the antenna design, and comparing the simulation and
measured results can be done for future work. The radiation characteristic of the
antenna can also be studied and analyzed for future work.
REFERENCE
[1] K. Fujimoto and J. R. James, Eds., Mobile Antenna Systems Handbook, 2nd ed.
Norwood, MA: Artech House, 2001.
[2] K. L. Wong, Planar Antennas for Wireless Communications, New Jersey: John Wiley &
Sons, 2003
[3] J. D. Kraus, Antennas, New York: McGraw-Hill Book Co., 1988.
[4] Z. Ying, “Multi frequency-band antenna,” PCT application WO01/91 233, May 2001.
[5] Di Nallo, C. Faraone, “A Multiband internal antenna for mobile phones” Electronics
LettersVolume 41, Issue 9, 28 April 2005 .
[6] SEMCADX reference manual 2006 , Schmid & Partner Engineering AG (SPEAG).
[7] David.M Pozar, Microwave Engineering, Third Edition, NJ: Wiley IE, 2005.
[8] John D Kraus, Ronald J Marhefka, Ahmad S Khan,Antenna for all application, 3rd
edition , McGraw-Hill,2006.
[9] Shun-Yun Lin, “Multiband folded planar monopole antenna for mobile handset”
Antennas and Propagation, IEEE Transactions on Volume 52, Issue 7, July 2004
[10] F. H. Blecher, “Advanced mobile phone service," IEEE Transactions on Vehicle
Communications, vol. VT-29, May 1980.
[11]. Ciais, P.; Staraj, R.; Kossiavas, G.; Luxey, C, “Compact internal multiband antenna for
mobile phone and WLAN standards” Electronics Letters Volume 40, Issue 15, 22 July 2004
[12] Shun-Yun Lin; “Multiband folded planar monopole antenna for mobile handset”
Antennas and Propagation, IEEE Transactions on Volume 52, Issue 7, July 2004.
[13] K.C. Gupta, Ramesh Garg, Inder Bahl, Prakash Bhartia, “Microstrip Lines and
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62
APPENDIX A: SEMCADX FEATURES AND OPTIONS LIST
63
64
APPENDIX B: RT/DUROID DATA SHEET
65
67
APPENDIX C: ELEMENT THICKNESS RESULTS
Element thickness 0.25mm
68
69
Element thickness 0.5mm
70
71
Element thickness 0.75mm
72
73
74
75
Element thickness of 1mm
76
77
77
APPENDIX D GROUND PLANE SIZE RESULTS
Ground plane size 70mm
78
79
Ground plane size 75mm
80
81
82
83
84
Ground plane size 85mm
85
86
Element length 90mm
87
88
89
GROUND PLANE SIZE 95MM
90
91
Element thickness 100mm
92
93
APPENDIX E: ANTENNA WITH PLASTIC RESULTS
Plastic thickness 0.25m
94
95
Plastic thickness 0.5mm
96
97
98
Plastic thickness 0.25
99
100
Plastic thickness 0.75mm
101
102
103
Plastic Thickness of 1.5mm
104
105
Plastic thickness 1.75mm
106
107
108
Plastic Thickness 1.25mm
109
110
Plastic thickness 2mm
111
112