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THE CHINESE UNIVERSITY OF HONK KONG
Design of Mobile Phone Antenna
Yip Wah Chun
香港中文大學電子工程學系
DEPARTMENT OF ELECTRONIC ENGINEERING
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Design of Mobile Phone Antenna
Author: Yip Wah Chun
Student I.D.: 03608183
Supervisor: Professor K.L. Wu
Associate Examiner: Professor K.N. Leung
A project report presented to the Chinese University of Hong Kong
in partial fulfillment of the Degree of Bachelor of Engineering
Department of Electronic Engineering The Chinese University of Hong Kong
April, 2007
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Abstract
In recent years, the demand for small and mobile communication devices,
especially the mobile phone, has grown rapidly. Devices having internal
antenna is a trend and is required for such applications Antenna size is a major
factor that limits device miniaturization. To decrease the size, antenna design
is base on microstrip antennas and planar inverted-F antennas (PIFA) which
have been used for handheld wireless devices because these antennas have
low-profile geometry and can be embedded into the mobile phone.
Nowadays, mobile phones are not only for voice communication but they are
required for operation in more than one frequency band.
Dual-band and tri-band phones have been now become a standard because of
the multiple frequency bands used for wireless applications.
Reducing antenna size generally degrades antenna performance. It is
therefore important to also examine the effect on the size reduce and
parameter tradeoffs for reducing the size. In the handheld environment,
antennas are mounted on a small ground plane. Ground plane size effects on
antennas are investigated
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Acknowledgements
I would to acknowledge Professor Wu Ke Li on the advice on the project. He
has a deep knowledge on electromagnetic wave that I can gain more
knowledge on it. Through the project, I learn how to use simulation tools to
design the antenna. All these meetings are a great help for this project.
I would to thank tutor Lam Fuk Ming who give many advice on the project.
Also, I have to thanks all the staffs in Microwave Laboratory for all the
supports.
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Content
Abstract .......................................................................................................................... I
Acknowledgements....................................................................................................... II
Content.........................................................................................................................III
Chapter 1- Introduction..................................................................................................1
1.1 Introduction......................................................................................................1
1.2 Thesis Outline ..................................................................................................2
Chapter 2 - Antenna of Mobile Unit ..............................................................................3
2.1 Small mobile phone antenna............................................................................3
2.1.1 Miniaturization..............................................................................................4
2.2 Bandwidth ........................................................................................................5
2.3 Reviews of Mobile Phone Antennas ................................................................5
2.4 Monopole .........................................................................................................6
2.5 Normal Mode Helical Antenna ........................................................................7
2.6 Meander Line Antenna.....................................................................................8
2.7 Inverted-L Antenna (ILA)................................................................................9
2.8 Inverted-F Antenna (IFA) ..............................................................................10
2.9 The meander Planar Inverted-F Antenna .......................................................12
Chapter 3 – Design of Antenna....................................................................................13
3.1 Overviews ......................................................................................................13
3.2 Design Tools ..................................................................................................13
3.3 Design Consideration.....................................................................................14
3.3.1 Location of Antenna............................................................................15
3.3.2 Ground plane effect.............................................................................16
3.3.3 Antenna Height Effect.........................................................................19
IV
Chapter 4 – Antenna Simulation ..................................................................................20
4.1 Dual band Mobile Phone Antenna .................................................................20
4.1.1 Return loss ..........................................................................................21
4.1.2 Current Distribution ............................................................................22
4.1.3 Radiation Pattern.................................................................................24
4.2 Triple band Antenna.......................................................................................25
4.2.1 Return Loss .........................................................................................26
4.2.2 Current Distribution ............................................................................27
4.2.3Radiation Pattern..................................................................................29
Chapter 5 – Antenna Implementation ..........................................................................31
5.1 Antenna Fabrication .......................................................................................31
5.1 Experimental Setup – Network Analyzer ......................................................33
5.2 S11 .................................................................................................................34
Conclusion ...................................................................................................................35
Reference .....................................................................................................................36
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Chapter 1- Introduction 1.1 Introduction
In the mobile communication, in the past decade, the industry has grown
significantly. In the past, the mobile unit has only for voice communication, it
has changed and more band and applications are need in a mobile phone
which may lead the mobile phone has multiple antenna.
In the mean time, the most of the mobile phone has been in internal antenna
elements instead of external whip and helix antennas used previously.[1] Also,
the space is very limited for antennas inside the casing of a mobile unit,
antennas with as small size as possible are needed. One great challenge in
the antenna development is to obtain compact antenna elements with
sufficient bandwidth and high efficiency.
We have to male the trade of between the different properties of the antenna
such as the size, bandwidth, gain, etc.[2] Besides, universal antenna elements
cannot be realized because the antenna performance depends strongly on the
size of the metal parts of the device and the location of the antenna on it.
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1.2 Thesis Outline
In this chapter, there is a brief introduction on mobile phone issue is stated on
discussed.
In chapter 2, there is a review on the mobile phone antenna, discussion on
different type antenna on mobile phone.
In chapter 3, design issues on the mobile phone antenna are investigated and
it showed how they affect the antenna.
In chapter 4, a design on the mobile phone antenna is mention and simulation
result is shown.
In chapter 5, it showed the antenna fabrication and measurements on the
antenna are carried out.
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Chapter 2 - Antenna of Mobile Unit
2.1 Small mobile phone antenna
In recent years, the mobile cells market has been growing rapidly all over the
world. One of the trends in mobile phone in the past few years has been to
reduce the size and weight of the mobile phone. This remarkable reduction in
the unit’s size has sparked a rapid evolution of the antennas used for mobile
phone.
Hence, the design of antennas for small mobile terminals is becoming more
challenging. The antennas are required to be smaller and smaller and their
performances have to be maintained. However, usually a degradation of the
gain and bandwidth are observed when the antenna’s size is reduced.
Furthermore, more than one antenna will be implemented in a mobile phone
as more applications are required today. As a result, the design of two or more
antennas on a small mobile phone is more challenging compared to the design
of a single conventional antenna in the mobile phone. [3]
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2.1.1 Miniaturization
To decrease the size of an antenna, the resonant frequency remains the same
even though the antenna size is reduced. Some of the parameters that may
suffer are:
1 Reduced efficiency (or gain)
2 Shorter range
3 Smaller useful bandwidth
4 Increased sensitivity to external factors
There are several means for miniaturization.
1 By loading the antenna in a way that the self-resonance is obtained when the
antenna volume is smaller than that of a basic structure.
2 By increasing the effective resonator length by bending the structure
according to some geometrical configuration, e.g. meandering.
Several techniques can be applied to further reduce the antenna size.
However we have to trade off the effect by applying different miniaturization
methods.[4]
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2.2 Bandwidth
For a small antenna, the term bandwidth typically refers to the impedance
bandwidth. The antenna should have an adequate bandwidth covering the
frequency range used by the required wireless communication system. The
requirements for operating frequency and bandwidth are different for each
system. Typically, the impedance bandwidth in cellular systems could be
defined as the return loss of Lretn > 6 dB for the whole operating frequency
range. [5]
2.3 Reviews of Mobile Phone Antennas
For the mobile communication systems in 1980s (the earliest mobile
communication), the typical mobile phone was nearly 600cc in volume and
approximately 850g in weight. The antenna used for the first phone was a half
wavelength monopole antenna. After many years of evolution, the volume for
the mobile phone had been reduced to less than 60cc and a weight of less
than 60g around 2000. it can see that the built-in antennas are more preferable
than the half-wavelength monopole antenna.
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2.4 Monopole
The quarter-wavelength monopole antenna is the fundamental mobile antenna
and has a simple structure as shown in Figure 2.1. However, a
quarter-wavelength monopole antenna caused large leakage currents to the
terminal case compared to the half-wavelength monopole antenna [6].
For a half-wavelength monopole, the maximum current amplitude occurs
around the center of the monopole therefore current amplitude around the feed
point (between the monopole and the terminal case) is small. However, for a
quarter-wavelength monopole the maximum current amplitude occurs around
the feed point and large current flows into the terminal case. Due to the
leakage currents, the length of the terminal case significantly changes the
radiation characteristics of an antenna.
Moreover, the 3/8 or 5/8 wavelengths monopole antennas have been
employed for mobile terminals as they have the appropriate input impedance
for matching to the feeding line and yet the current flow on the terminal case is
very small. This antenna is also named as the “whip” antenna.
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Fig 2.1 - 1/4-wavelength monopole antenna
2.5 Normal Mode Helical Antenna
In the normal mode, the dimensions of the helix are small compared with the
wavelength. The far field radiation pattern is similar to an electrically short
dipole or monopole. These antennas tend to be inefficient radiators and are
typically used for mobile communications where reduced size is a critical factor.
A Tesla coil secondary coil is also an example. Figure 2.2 show a structure of a
helix
Fig 2.2 - Geometrical configuration of a helix
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2.6 Meander Line Antenna
This antenna define as an antenna with the wire folded back and forth where
resonance is found in a much more compact structure than can otherwise be
obtained.
For example we can shorten a monopole by using a printed meander pattern
instead of a helical as shown in Figure 2.3. Meander line antenna is also a
physically small but electrically large antenna.
A planar and compact meander line antenna has been studied [7]. Multi-band
characteristics can be accomplished by connecting two or more λ/4 meanders
in parallel with each being tuned to its own frequency as shown in Figure 2.4.
Fig 2.3 Meander printer antenna
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Fig 2.4 Dual-band meander line antenna.
2.7 Inverted-L Antenna (ILA)
The inverted-L antenna is an end-fed short monopole with a horizontal wire
element placed on top that acts as a capacitive load. Figure 2.4 shows the
structure of the inverted-L antenna. The inverted-L antenna is an attractive
alternative because of its simple layout. The design is uncomplicated and can
be easily manufactured with low cost materials.
Additionally, many of the electrical characteristics of the inverted-L are similar
to those of the well understood short monopole.
The ILA has low input impedance as its input impedance is equal to that of the
short monopole plus the reactance of the horizontal element closely placed to
the ground plane.
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Fig. 2.4 – Structure of Inverted-L antenna
2.8 Inverted-F Antenna (IFA)
Most of the new mobile terminals (e.g. GSM phones) have built-in antennas
which are not extruded from the terminal’s exterior. Generally, the very top of
the phone is not the best position to place the antenna because the antenna
element should be kept away from the user to avoid unnecessary losses. Also,
the antenna should not be placed too low on the back of the phone either as
such a position will increase the antenna’s losses due to the users’ hand.
Therefore, the surface on the upper back of the phone is a preferable position
to place the built-in antenna. The well known built-in antennas i.e. Inverted
F-antenna (IFA) and PIFA have been widely used in most of current mobile
terminals.
The IFA is originally transformed from an inverted-L antenna (ILA) which
consists of a short monopole as a vertical element and a wire horizontal
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element attached at the end of the monopole. The ILA is a low profile antenna
as the height of the vertical element is usually much less than a wavelength.
The horizontal element normally has a length of about a quarter wavelengths.
The planar version of the inverted-F antenna, the planar inverted-F antenna (PIFA),
meets the specifications which are required in a reduced size environment as shown in
figure.2.5.
The common characteristics of the PIFA have been analyzed in [8] The
shorting pin is positioned at the corner of the planar element to yield a
maximum reduction in the antenna’s size. The narrower the shorting plate
width, W, the lower the resonant frequency of the PIFA. The resonant
frequency (f) of the PIFA can be determined from the equation below
f =c/ 4(L1+L2) (3.1)
where L1 is the width of PIFA, L2 is the length of PIFA and c is the speed of light
in free space.
Figure 2.5 – Structure of Planar Inverted-F Antenna
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2.9 The meander Planar Inverted-F Antenna
One other variation of the PIFA is introduced with the meander like structure, it
has a further reduction in size while still maintaining adequate bandwidth. The
bandwidth still maintained and the size is only an eighth of a wavelength long.
The meander PIFA is modification of the conventional PIFA design that is
slightly reduced in size from the conventional PIFA. It uses several slits cut
laterally in the PIFA radiating element. These slits effectively act to increase
the electrical length of the antenna and allow for reduced overall antenna
volume.
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Chapter 3 – Design of Antenna
3.1 Overviews
The mobile phone antenna to be designed is based on the structure of the
Planar Inverted-F Antenna. The idea is to cut slot on the planar element of a
PIFA, sp that the antenna can work as a multi-band PIFA. As shown in figure
3.1, the basic principle is that the longer arm resonates at low band whilst
shorter arm resonates at high band.
Figure 3.1 – Structure of a dual band antenna
3.2 Design Tools
The Cellular PIFA was simulated using a commercial 2.5D Method of Moments
code (IE3D). The reason to use IE3D is that It use the moment method codes
use an integral equation formulation combined with a matrix method to solve
the antenna characteristics. The surface nature of the integral equation
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formulation makes it particularly suited to solving wire and surface geometries.
Moment method codes have the advantage of typically being computationally
faster than other numerical analysis methods
3.3 Design Consideration
The dimensions of the phone may vary a lot depending on the handset design.
In current mono block mobile phone, the typical length is in the range of 80-
140 mm, the width in the range of 40-60 mm, and the thickness a few
millimeters. For the phones with a slider, the phone dimensions change in
different use positions.
Beside, antenna location and antenna height can affect the performance of the
antenna. The bandwidth and efficiency can be varied with changing the above
parameters.
A rough design of the antenna is designed as follow: Different parameter of the
antenna is studied then.
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Figure 3.2 – Structure of the mobile phone antenna (dimension in mm)
3.3.1 Location of Antenna
The location of the antenna is studied to find the best position to locate the
antenna.
The antenna’s position is varied from top of the antenna to see its effect on the
performance of the antenna. Its effect on the bandwidth of antenna is plotted
as follow:
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Location of Antenna
0
1
2
3
4
5
0 10 20 30 40 50
Location (mm)
Ban
dWid
th (
%)
Frequency-900MHz
Frequency-1800MHz
Figure 3.3 – Effect of different location of antenna
3.3.2 Ground plane effect
It is studied that most of the antennas used in current mobile phones are small
unbalanced antennas for which the ground plane is an important factor. This
can includes inverted-F antennas (IFA), planar inverted-F antennas (PIFA),
and their derivatives. When it is attached to a relative small finite ground plane,
some of the properties of these antennas can be very different from those of
the same antennas on a large or infinite ground plane.
There is a strong influence of the mobile size on the antenna parameters. The
effect of a small ground counterpart has also been noticed in [5] in a different
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context.
Figure. 3.4 shows the results for a length of the mobile phone antenna ground
plane ranging from 80 mm to 150 mm. It is noticed that a strong effect which.
the impedance bandwidth of the antennas rises until the mobile reaches a
certain length
Ground Plane Effect
0
1
2
3
4
5
6
7
8
9
80 90 100 110 120 130 140 150
Ground Plane (mm)
rel.
Ban
dwid
th -
10dB
(%
)
Frequency-900MHz
Frequency-1800MHz
Figure 3.4 Effect of ground plane on bandwidth
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Beside, its effect on the resonant frequency of the antenna is showed in figure
3.5, it can see that the resonant frequency is not much affected by the size of
the ground.
Effect on Fr
0
500
1000
1500
2000
80 90 100 110 120 130 140 150
mm
Freq
uen
ct(M
Hz)
1800
900
Figure 3.5 Effect of ground plane on resonant frequency
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3.3.3 Antenna Height Effect
It is known that in PIFA, the antenna height has a effect on the performance of
the antenna. Figure 3.6 shows that the antenna height effect on the bandwidth
of the antenna. It is noticed that as antenna height increase the bandwidth
increase.
Effect of Antenna Height
0
1
2
3
4
5
6
2 3 4 5 6 7 8
Height (mm)
Ban
dwid
th (
%)
Frequency-900MHz
Frequency-1800MHz
Figure 3.5 – Antenna height effect on bandwidth
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Chapter 4 – Antenna Simulation
4.1 Dual band Mobile Phone Antenna
After studied the factors that affect the antenna, a dual band mobile phone
antenna is designed. The dimension of the ground of the antenna is 40mm ×
110mm, the size of the antenna part is 40mm × 30mm, with a height of 7mm. Figure 4.1
show the top view of the mobile phone antenna and figure4.2 show the slide view of the
mobile phone antenna
Figure4.1 Top view of the antenna
Figure 4.2 Side view of the antenna
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4.1.1 Return loss
The return loss is plotted in figure4.3, it can show that the antenna work on the
desired frequency band, 900MHz and 1800MHz.
Figure 4.3 Return loss of the dual band mobile phone antenna
For the 10bB bandwidth efficiency, at 900MHz, the bandwidth is 8.7%, at
1800MHz, the bandwidth is 3.8%.
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4.1.2 Current Distribution
The vector and average current distribution of the antenna at 900MHz and
1800MHz are showed in figure 4.4 and they are compared with that in 500MHz
and 2100MHZ
Figure 4.4a Current distribution at 900MHz
Figure 4.4b Current distribution at 1800MHz
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Figure 4.4cCurrent distribution at 500MHz
Figure 4.4dCurrent distribution at 2100MHz
It is obvious that the current distribution is denser in the operating band.
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4.1.3 Radiation Pattern
The radiation patterns are shown is figure 4.5
Figure 4.5a Pattern view of the antenna at 900MHz
Figure 4.5b Pattern view of the antenna at 1800MHz
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4.2 Triple band Antenna
The antenna is used the Dual inverted-F antenna geometry together with a
meander structure to obtain the desired frequency range.
The structure of the antenna is shown in figure 4.6
Figure 4.6 structure of the antenna
Part Length (mm) Width (mm)
a 30 9
b 30 6
c 30 6.5
d 29 6.5
e 28.8 6
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4.2.1 Return Loss
The return loss is plotted in figure4.7, it can show that the antenna work on the
GSM band and has a third band at 2.5GHz
Figure 4.7 Return loss of the triple band antenna
For the 10bB bandwidth efficiency, at 900MHz, the bandwidth is 7.6%, at
1800MHz, the bandwidth is 4.8%. For the third band, it has a 6dB bandwidth
which is 2.5%.
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4.2.2 Current Distribution
The vector and average current distribution of the antenna at 950MHz and
1800MHz and 2450MHz are showed in figure 4.4 and they are compared with
that in 500MHz
Figure 4.8a Current distribution at 900MHz
Figure 4.8a Current distribution at 1800MHz
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Figure 4.8a Current distribution at 2450MHz
Figure 4.8a Current distribution at 500MHz
It can see that the current is denser in the operating frequency.
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4.2.3Radiation Pattern
The pattern views are compared in figure 4.9
Figure 4.9a Pattern view of the antenna at 930MHz
Figure 4.9b Pattern view of the antenna at 1880MHz
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Figure 4.9b Pattern view of the antenna at 2450MHz
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Chapter 5 – Antenna Implementation
After the antenna is simulated as shown in Chapter 4, the antenna is fabricated
using fr4 as the material. It has 0.8mm thick with a dielectric constant 2.2.
5.1 Antenna Fabrication
The fabrication of the antenna is carried out in the darkroom and the fabricated
antenna is shown in figure 5.1.
Figure 5.1a Dual band antenna
Figure 5.1b Top view of dual band antenna
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Figure 5.1c Triple band antenna
Figure 5.1d Top view of triple band antenna
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5.1 Experimental Setup – Network Analyzer
R3767CG Network Analyzer is a microwave measurement system, which can
determine the S-Parameters for a given two-port device. The S-Parameter is in
the form of a four scattering matrix and S11, S12, S21, S22 have both
amplitude and phase values.
Figure 5.2 R3767CG Network Analyzer
For the test equipment, it may exist some errors and alters the measurement
result. Therefore, before taking the measurement, an error correction process
should be performed by Calibration. This calibration is to let the Network
Analyzer measure the standards (i.e. open circuit, short circuit and precision
load impedance) provided in the Calibration Kit.
This calibration can remove directivity, source match and reflection tracking
from reflection measurements
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5.2 S11
The return loss of the dual band antenna is shown in figure5.3 , it is noticed
that the resonant frequency has a shift to the desired frequency band.
Figure 5.3 Return loss of antenna
The error can be due to the fabrication of the antenna is not perfect enough.
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Conclusion
In conclusion, in designing an antenna for mobile phone, there are many
factors that need to be considered. Today, mobile phone has many types, such
as mono block, slide, fold and swivel, So far it has been impossible to make
the universal antenna (module), because different form factors have different
requirements on antenna shape and placemen
The antennas suggested in this project can work on dual band or triple band
which is suitable for GSM and some application.
Also, the mobile phones are requiring more and more application beside the
voice communication, and it would become more complicated and challenging.
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Reference
[1] L. Setian, Practical Communication Antennas with Wireless Applications,
Prentice Hall PTR, New Jersey: 1998.
[2] Design Guide for Wireless Device Antenna Systems, Centurion Wireless
Technologies, Inc, 2000
[3] Multi band, multi antenna system for modern mobile terminal, Zhinong
Ying and Johan Anderson, IEEE 2003
[4] O. Lehmus, Miniaturization methods of handset antennas, Master’s
Thesis, Helsinki University of Technology, Radio Laboratory, Espoo,
Finland, Feb. 1999, 99 p.
[5] J. Toftgård, S. N. Hornstleht, and J. B. Andersen, “Effects on portable
antennas of the presence of a person,” IEEE Trans. Antennas Propagat.,
vol. 41, no. 6, June 1993, pp.739-746.
[6] K. Hirisawa and M. Haneishi, Analysis, Design, and Measurement of
small and Low-Profile Antennas, Artech House, Boston: 1992.
[7] A.B. Smolders, Microstrip Phased-Array Antennas: A Finite-Array
Approach, Thesis Report, Endhoven University of Technology, 1994,
[8] K. Hirasawa, and M. Haneishi, Design, and Measurement of Small and
Low-profile Antennas, MA: Artech House, 1991.