chapter i introducing of the microstrip antenna -...
TRANSCRIPT
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Chapter I
Introducing of the Microstrip Antenna
1.1 Introduction
Microstrip antenna is a printed type of antenna consisting of a dielectric substrate
with relative permittivity and permeability
where
sandwiched in between a ground plane and a metallic patch. The concept of
microstrip antenna was first proposed in 1953, twenty years before the practical
antennas were produced [1].
Since the first practical antennas were developed in early 1970's, interest in this
kind of antenna increase and in 1979 the first professional meeting on micro strip
antennas was held in New Mexico. The microstrip antenna is physically very simple
and flat, these are two of the reasons for the great interest in this type of antenna.
Microstrip antennas have several advantages compared to other bulky type of
antennas. Some of the main advantages of micro strip antennas are that it has low
fabrication cost, its lightweight, low volume, and low profile configurations that it
can be made conformal, it can be easily be mounted on rockets, missiles and
satellites without major modifications and arrays of these antennas can simply be
produced [2].
However, micro strip antennas have some drawbacks including narrow bandwidth,
low power handling capability and low gain. But with technology advancement and
extensive research into this area these problems are being gradually overcome.
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In many practical designs, the advantages of microstrip antennas far outweigh their
disadvantages. With continuing research and development it is expected that micro
strip antennas will replace conventional antennas for most applications. Some of the
notable applications for microstrip antennas are in the areas of mobile satellite
Communications, the Direct Broadcast Satellite (DBS) system and Global
Positioning System (GPS). Microstrip antennas also found useful in non-satellite
based application such as remote sensing and medical hyperthermia application.
1.2 General Description
In its simplest form, micro strip antenna is a dielectric substrate panel sandwiched in
between two conductors. The lower conductor is called ground plane and the upper
conductor is known as patch. Microstrip antenna is commonly used at frequencies
from to 100 GHz and at frequencies below ultra high frequency, UHF micro strip
patch become exceptionally large. The radiating patch can be design in various
shapes according to the desired characteristics. Illustrated in Figure 1.1 is the
simplest structure of a rectangular microstrip patch antenna.
Figure 1.1 Microstrip Patch Antenna Layout
1.2.1 Conducting Layers
The common materials used for conducting surfaces are copper foil or copper foil
plated with corrosion resistant metals like gold, tin and nickel. These metals are the
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main choice because of their low resistivity, resistant to oxidation, solderable, and
adhere well to substrate.
An alternative to metal for conducting surface is to use conductive ink. It is easier to
fabricate but have three disadvantages. First, is that conductive inks cannot be
soldered in the usual way, to overcome this solder pastes are used. Secondly is
oxidation, but the effect is negligible since the oxide is also conductive. The third is
the problem of silver ion migration. Silver ions tend to migrate under humid
conditions and this will cause a short across the conductive ink lines.
1.2.2 Dielectric Substrate
The first step in designing micro strip antenna is to choose the suitable substrate.
There are various types of substrate available in market that provides considerable
flexibility in the choice of a substrate for particular applications.
In most cases, considerations in substrate characteristics involved the dielectric
constant and loss tangent and their variation with temperature and frequency,
dimensional stability with processing, homogeneity and isotropicity. In order to
provide support and protection for the patch elements, the dielectric substrate must
be strong and able to endure high temperature during soldering process and has high
resistant towards chemicals that are used in fabrication process.
The surface of the substrate has to be smooth to reduce losses and adhere well to the
metal used. Substrate thickness and permittivity determine the electrical
characteristics of the antenna. Thicker substrate will increase the bandwidth but it
will cause the surface waves to propagate and spurious coupling will happen. This
problem however, can be reduced or avoided by using a suitably low permittivity
substrate. Below are six categories of dielectric material that are used for substrates.
(1) Ceramic - Alumina ( r = 9.5, tan (δ) = 0.0003)
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This type of dielectric has low loss but brittle. It has high frequency applications and
also has excellent resistance against chemicals. The temperature range for alumina is
up to 1600oC.
(2) Synthetic materials - Teflon ( r = 2.08, tan (δ) = 0.0004)
These materials possess good electric properties but have a low melting point and
have poor adhesion. The dimensional stability for this substrate is relatively poor
but reinforcement with glass or ceramic will improve the dimensional stability to
fairly good.
(3) Composite materials – Duroid ( r = 2.2 /6.0/ 10.8, tan (δ) = 0.0017)
Composite materials are a mixture of fiberglass and the synthetic materials cited
above. These materials have good electrical and physical properties and excellent
dimensional stability.
(4) Ferromagnetic - Ferrite ( r = 9 - 16, tan (δ) =0.001)
This type of dielectric is biased by an electrical field. The resonant ftequency of the
antenna depends upon the biasing; hence magnetically tuneable antennas are
possible.
(5) Semiconductor - Silicon ( r = 11.9, tan (δ) =0.0004)
This type of dielectric can be integrated into circuit, but only small areas are
available so it is not suitable for antenna applications.
(6) Fiberglass - Woven fiberglass ( r = 4.882, tan () = 0.002)
This material is relatively low in cost for such low loss tangent. However, woven
fibers tend to be anisotropic and this is undesirable in many designs [3].
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1.2.3 Configurations
Since the early development of microstrip antenna until now, a variety of
configurations have been produced and investigated to improve the performance of
microstrip antenna. Some of the common shapes are rectangle, triangle and circular.
Several shapes such as pentagon and ellipse are known to give circular polarization.
Instead of using just one patch, microstrip antenna has been combined in many ways
to improve the antenna characteristics.
By arranging patches side by side on the same substrate to produce a flat array for
example will give higher directivity and gain. A wider bandwidth can be achieved if
antennas are stacked on top of each one another with gaps in between.
Shown in Figure 1.2 below are some of the shapes that have been investigated for
micro strip patch.
Figure 1.2 Some Shapes of a Microstrip Antenna
1.2.4 Microstrip Feeds
Matching is usually required between the antenna and the feed line, because antenna
input impedances differ from customary 500hm line impedance. An appropriately
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selected port location will provide matching between the antenna and its feed line.
And the location of the feed line also affects the radiation characteristics. There are
three common techniques for exciting a particular microstrip antenna. These are
coaxial probe, microstrip line and aperture coupling.
The coaxial probe is the most popular technique and is illustrated in Figure 1.3. The
coaxial connector is attached to the ground plane and the coaxial center conductor
extends through the substrate and is attached to the radiating patch. For coaxial
probe the location of the feed is normally located at one third of the distance from
the center of the patch to the side. The advantages of this method are that the probe
location can selectively excite additional modes and it can be use with plated vias
for multi layer circuits.
Figure 1.3 Coaxial feed
In the second technique, micro strip line is connected directly to the radiating patch;
see Figure 1.4. The location of the feed line may affect a small shift in resonant
frequency, due to the change in coupling between the feed line and the antenna. This
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technique provide good polarization however, it is very difficult to minimize the
spurious radiation from the microstrip line. Spurious radiation will increase
sidelobes on the radiating pattern.
Figure 1.4 Microstrip Line Feed
In the aperture coupling the feed line and the patch are on different sides of the
ground plane as shown in Figure 1.5. A slot is cut in the ground plane to couple the
electromagnetic to the radiating patch, thus no via connectors needed. This technique
is to avoid spurious radiation escapes from the feed line and corrupt the sidelobes or
polarization of the antenna.
Figure 1.5 Aperture coupling feed
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1.2.5 Losses in Microstrip
The dissipative losses associated with microstrip lines are one of the major
limitations with the micro strip antenna. That is why it is important to find new
ways to reduce this loss without jeopardizing the geometrical simplicity of an
antenna.
There are three types of micro strip line losses; these are ohmic loss, dielectric loss
and radiation loss. The ohmic loss is cause by the finite conductivity of the metal
forming the circuit. The dielectric loss is a measure of the energy dissipated within
the substrate. Power loss is due to radiation occurs at discontinuities in the micro
strip such as open ends, splitters and impedance steps.
1.3 Bandwidth
Antenna bandwidth is basically the range of frequencies over which essential
performance parameters are satisfactory. There is no unique definition for
satisfactory performance and this will differ £Tom application to application. With
f A and f B be the upper and lower frequencies for which satisfactory performance
is obtained. And fC is the center frequency (or sometimes the design frequency).
Then bandwidth as a percent of the center frequency, represented as % B is given
by
B= (fA - fB)/fC x100% (1-1)
Bandwidth is also can be defined as a ratio
by
B= fA/ fB (1-2)
The second equation is used for wideband antennas, where bandwidth is expressed
in ratio. Microstrip antenna is categorized as narrowband antenna, and the bandwidth
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is usually expressed as a percent using Equation 1.5. Antenna with fA/ fB = 2 or
more is classified as broadband antenna.
1.4 Polarization
The polarization of an antenna in a given direction from the antenna is the
polarization of the wave transmitted by the antenna. The polarization in a given
direction is that of the local plane wave at points on a radiation sphere centered on
theantenna. Thus, polarization is that of what the wave is radiated when the antenna
is transmitting. Most antennas are reciprocal, and the transmitting and receiving
polarization properties are identical.
There are three most common antenna polarization are linear polarization, elliptical
polarization and circular polarization. Linearly polarization is achieved when
electric field vector moves back and forth along a line; see Figure 1.6 whereas the
axial ratio is zero or infinite while the title angle gives the orientation. A general
elliptical polarization is as shown in Figure 1.7a and 1.7b is characterized by three
quantities which are the axial ratio, title angle and the sense of rotation . The wave
that produced elliptical polarization is travelling in the +z-direction, with rotation
can be either to the left or right. If it rotates counter-clockwise, it is right-hand
polarized.
Circularly polarized (Figure 1.8a and 1.8b) is produced when electric field vector
remains constant with length but rotates around a circular path, the rotation can be
either to the left or to the right. circular polarization is obtained for unit axial ratio,
where the title angle losses its meaning. accordingly, the quality of the circular
polarized is determined by the axial ratio.
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Antenna can give circular polarization if two orthogonal components with equal
amplitude but the quadrature are radiated but if that amplitudes are not equal then the
antenna will give elliptical polarization
Figure 1.6 Linear Polarizations
Fig 1.7 Elliptical Polarizations
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Figure 1.8 Circular Polarizations
The polarization of a simple micro strip antenna such as rectangular and circular
patch is normally linear. However, for corner feeding rectangular patch, circular
polarization may be obtained with a single excitation. Circular polarization may be
obtained also in circular patch by exiting two orthogonal modes of the antenna with
signals 900 out of phase. There are some microstrip antennas that are found to have
circular polarization using a single feed, such as triangular, pentagonal and elliptical.
Circular polarization is especially important in the design of antenna arrays.
1.5 Radiation Field
Radiation of the micro strip antenna occurs trom the mnging fields between the edge
of the microstrip antenna radiation patch and the ground plane. At high trequencies
the radiation loss of the antenna is much larger than conductor and dielectric losses.
When fabricated on thick, low dielectric constant substrates open-circuited
microstrip lines radiate more power.
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Now consider a simple case of a rectangular microstrip antenna spaced a small
traction of a wavelength above ground plane, as shown in Figure 1.9(a). With the
assumption that there are no variations of the electric field along the thickness and
width of the microstrip patch, the electric field of the radiator is illustrated in Figure
1. 9(b). The patch length is about half of a wavelength (λ/2) and the radiation fields
differ along the length. Radiation of the antenna is mostly resulted from the fringing
fields along the open circuited edges of the patch. This fringing fields can be
resolved into two components; normal and tangential components with the respect to
the ground plane.
The tangential components, which are parallel to the ground plane, are in phase and
the resulting fields give the maximum radiated field normal to the surface to the
structure. Consequently, the patch can be represented by two slots λ/2 apart and
radiating in the half space above the ground plane; see Figure 1.9(c). The normal
components are out of phase because the patch line is λ/2 long, thus the far field
produced by them cancel in the broadside direction. With the same consideration to
the variation field along the width of the patch, microstrip antenna may be
represented by four slots surrounding the patch.
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Figure 1.9 (a) Rectangular micro strip antenna; (b) Side View; (c) Top View
1.6 Methods of Analysis
The most popular models for the analysis of Microstrip patch antennas are the
transmission line model, cavity model, and full wave model (which include primarily
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integral equations/Moment Method). The transmission line model is the simplest of
all and it gives good physical insight but it is less accurate. The cavity model is more
accurate and gives good physical insight but is complex in nature. The full wave
models are extremely accurate, versatile and can treat single elements, finite and
infinite arrays, stacked elements, arbitrary shaped elements and coupling. These give
less insight as compared to the two models mentioned above and are far more
complex in nature.
1.6.1 Transmission Line Model
This model represents the microstrip antenna by two slots of width W and height h ,
separated by a transmission line of length L. The microstrip is essentially a no
homogeneous line of two dielectrics, typically the substrate and air.
Figure 1.10 Microstrip Line
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Figure 1.11 Electric Field Lines
The edge of the patch acts approximately as cavity with perfect electric conductor on
the top and bottom surfaces and perfect magnetic conductor on the sides. Hence, as
seen from Figure 1.11, most of the electric field lines reside in the substrate and parts
of some lines in air. As a result, this transmission line cannot support pure transverse
electric- magnetic (TEM) mode of transmission, since the phase velocities would be
different in the air and the substrate. Instead, the dominant mode of propagation
would be the quasi-TEM mode. Hence, an effective dielectric constant ( ) must
be obtained in order to account for the fringing and the wave propagation in the line.
The value of is slightly less than because the fringing fields around the
periphery of the patch are not confined in the dielectric substrate but are also spread
in the air as shown in Figure 1.11 above. The expression for is given by
Balanis as:
wheff
/121
1
2
1ε
2
1ε rr (1-3)
Where
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Consider Figure 1.12 below, which shows a rectangular microstrip patch antenna of
length L , width W resting on a substrate of height h . The co-ordinate axis is selected
such that the length is along the x direction, width is along the y direction and the
height is along the z direction.
Figure 1.12 Microstrip Patch Antenna
In order to operate in the fundamental mode, the length of the patch must be
slightly less than λ / 2 where λ is the wavelength in the dielectric medium and is
equal to where is the free space wavelength. The mode implies
that the field varies one λ / 2 cycle along the length, and there is no variation along
the width of the patch. In the Figure 1.13 shown below, the microstrip patch antenna
is represented by two slots, separated by a transmission line of length L and open
circuited at both the ends. Along the width of the patch, the voltage is maximum and
current is minimum due to the open ends. The fields at the edges can be resolved into
normal and tangential components with respect to the ground plane.
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Figure 1.13 Top and Side View of Antenna
It is seen from Figure 1.13 that the normal components of the electric field at the two
edges along the width are in opposite directions and thus out of phase since the patch
is λ / 2 long and hence they cancel each other in the broadside direction. The
tangential components (seen in Figure 1.13), which are in phase, means that the
resulting fields combine to give maximum radiated field normal to the surface of the
structure. Hence the edges along the width can be represented as two radiating slots,
which are λ / 2 apart and excited in phase and radiating in the half space above the
ground plane. The fringing fields along the width can be modeled as radiating slots
and electrically the patch of the microstrip antenna looks greater than its physical
dimensions. The dimensions of the patch along its length have now been extended on
each end by a distance ΔL , which is given empirically by Hammerstad as:
)8.0/()258.0ε(
)264.0/)(3.0ε(412.0
eff
eff
hw
hwhL (1-4)
The effective length of the patch now becomes:
(1-5)
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For a given resonance frequency , the effective length is given by as:
eff
efff
cL
02 (1-6)
For a rectangular Microstrip patch antenna, the resonance frequency for any
mode is given by James and Hall as:
(1-7)
Where m and n are modes along L and W respectively.
For efficient radiation, the width W is given by Bahl and Bhartia as:
0
1/2
r
2f
1)/2]c[(εW
(1-8)
The electical field of the rectangular patch antenna with respect (m,n) cavity modes
as:
(1-9)
and the surface current on the bottom of the patch is x directed as:
(1-10)
where is absolute magnetic constant is relative magnetic constant.
1.6.2 Cavity Model
Although the transmission line model discussed in the previous section is easy to use,
it has some inherent disadvantages. Specifically, it is useful for patches of
rectangular design and it ignores field variations along the radiating edges. These
disadvantages can be overcome by using the cavity model. A brief overview of this
model is given below.
In this model, the interior region of the dielectric substrate is modeled as a cavity
bounded by electric walls on the top and bottom. The basis for this assumption is the
following observations for thin substrates ( h << λ ) .
• Since the substrate is thin, the fields in the interior region do not vary much in the z
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direction, i.e. normal to the patch.
• The electric field is z directed only, and the magnetic field has only the transverse
components and in the region bounded by the patch metallization and the
ground plane. This observation provides for the electric walls at the top and the
bottom.
Figure 1.14 Charge distribution and current density creation on
the microstrip patch
Consider Figure 1.14 shown above. When the microstrip patch is provided power, a
charge distribution is seen on the upper and lower surfaces of the patch and at the
bottom of the ground plane. This charge distribution is controlled by two
mechanisms-an attractive mechanism and a repulsive mechanism as discussed by
Richards. The attractive mechanism is between the opposite charges on the bottom
side of the patch and the ground plane, which helps in keeping the charge
concentration intact at the bottom of the patch. The repulsive mechanism is between
the like charges on the bottom surface of the patch, which causes pushing of some
charges from the bottom, to the top of the patch. As a result of this charge movement,
currents flow at the top and bottom surface of the patch. The cavity model assumes
that the height to width ratio (i.e. height of substrate and width of the patch) is very
small and as a result of this the attractive mechanism dominates and causes most of
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the charge concentration and the current to be below the patch surface. Much less
current would flow on the top surface of the patch and as the height to width ratio
further decreases, the current on the top surface of the patch would be almost equal
to zero, which would not allow the creation of any tangential magnetic field
components to the patch edges. Hence, the four sidewalls could be modeled as
perfectly magnetic conducting surfaces. This implies that the magnetic fields and the
electric field distribution beneath the patch would not be disturbed. However, in
practice, a finite width to height ratio would be there and this would not make the
tangential magnetic fields to be completely zero, but they being very small, the side
walls could be approximated to be perfectly magnetic conducting .
Since the walls of the cavity, as well as the material within it are lossless, the cavity
would not radiate and its input impedance would be purely reactive. Hence, in order
to account for radiation and a loss mechanism, one must introduce a radiation
resistance and a loss resistance . A lossy cavity would now represent an
antenna and the loss is taken into account by the effective loss tangent which is
given as:
(1-11)
Where is the total antenna quality factor and has been expressed the form:
(1-12)
represents the quality factor of the dielectric and is given as :
(1-13)
where
is the angular resonant frequency.
is the total energy stored in the patch at resonance.
is the dielectric loss.
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is the loss tangent of the dielectric.
represents the quality factor of the conductor and is given as :
(1-14)
Where
is the conductor loss.
Δ is the skin depth of the conductor.
H is the height of the substrate.
represents the quality factor for radiation and is given as:
(1-15)
where is the power radiated from the patch.
Substituting equations (1-12), (1-13), (1-14) and (1-15) in equation (1-10), we get
(1-16)
Thus, equation (1-14) describes the total effective loss tangent for the microstrip
patch antenna.
1.6.3 Full Wave Solutions-Method of Moments
One of the methods, that provide the full wave analysis for the microstrip patch
antenna, is the Method of Moments. In this method, the surface currents are used to
model the microstrip patch and the volume polarization currents are used to model
the fields in the dielectric slab. It has been shown by Newman and Tulyathan how an
integral equation is obtained for these unknown currents and using the Method of
Moments, these electric field integral equations are converted into matrix equations
which can then be solved by various techniques of algebra to provide the result. A
brief overview of the Moment Method described by Harrington is given below.
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The basic form of the equation to be solved by the Method of Moment is:
(1-17)
where F is a known linear operator, g is an unknown function, and h is the source or
excitation function. The aim here is to find g , when F and h are known. The
unknown function
g can be expanded as a linear combination of N terms to give:
(1-18)
where is an unknown constant and is a known function usually called a basis or
expansion function. Substituting equation (1-16) in (1-15) and using the linearity
property of the operator F , we can write:
(1-19)
The basis functions must be selected in such a way, that each in the above
equation can be calculated. The unknown constants cannot be determined directly
because there are N unknowns, but only one equation. One method of finding these
constants is the method of weighted residuals. In this method, a set of trial solutions
is established with one or more variable parameters. The residuals are a measure of
the difference between the trial solution and the true solution. The variable
parameters are selected in a way which guarantees a best fit of the trial functions
based on the minimization of the residuals. This is done by defining a set of N
weighting (or testing) functions { } = , ,..... = in the domain of the
operator F . Taking the inner product of these functions, equation (1-17) becomes:
(1-20)
where m = 1,2,.....N
Writing in Matrix form, we get:
(1-21)
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Where
The unknown constants can now be found using algebraic techniques such as LU
decomposition or Gaussian elimination. It must be remembered that the weighting
functions must be selected appropriately so that elements of { } are not only
linearly independent but they also minimize the computations required to evaluate
the inner product. One such choice of the weighting functions may be to let the
weighting and the basis function be the same, that is, . = This is called as the
Galerkin’s Method as described by Kantorovich and Akilov.
From the antenna theory point of view, we can write the Electric field integral
equation as:
(1-22)
where
E is the known incident electric field.
J is the unknown induced current.
is the linear operator.
The first step in the moment method solution process would be to expand J as a finite
sum of basis function given as:
(1-23)
where is the basis function and is an unknown coefficient. The second step
involves the defining of a set of M linearly independent weighting functions, j w .
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Taking the inner product on both sides and substituting equation (1-22) in equation
(1-19) we get:
(1-24)
Where j = 1,2,.....M
Writing in Matrix form as,
(1-25)
where
J is the current vector containing the unknown quantities.
The vector E contains the known incident field quantities and the terms of the Z
matrix are functions of geometry. The unknown coefficients of the induced current
are the terms of the J vector. Using any of the algebraic schemes mentioned earlier,
these equations can be solved to give the current and then the other parameters such
as the scattered electric and magnetic fields can be calculated directly from the
induced currents. Thus, the Moment Method has been briefly explained for use in
antenna problems. The software used in this thesis, ADVANCE DESIGN SYSTEM
(ADS) is a Moment Method simulator which will be used for design and simulation
in this thesis.
1.7 Commercial Applications for Microstrip Antennas
Due to reduction in manufacturing cost and the simplified design process using
ADVANCE DESIGN SYSTEM (ADS), the microstrip antenna has been increasingly
in demand in the commercial sector. The current satellite communication
applications benefit greatly from the compactness, lightweight and low profile of the
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micro strip antenna. The commercial applications of micro strip antenna are
discussed in the next sections.
1.7.1 Mobile Satellite Communications
Mobile satellite communication can be accomplished by using either a few sets of
fixed geostationary station or a larger number of low Earth-orbiting satellites.
An example of the geostationary satellite systems is International Maritime Satellite
System (lNMARSAT), which uses frequencies in the L-band. The INMARSAT
version for land application, Standard-M terminal uses a briefcase size microstrip
array antenna. The antenna uses six circular patches and provides the gain of 14.5
dB. Toyota Central R&D Labs have produced phased array antennas that can be
steered electronically. It consists of 19 dual stacked patches to cover both
transmitting and receiving frequency bands.
1.7.2 Global Positioning System (GPS)
GPS is funded by and controlled by the U. S. Department of Defense (DOD). The
GPS system was originally designed for and operated by the U. S. military. The
satellite-based GPS has grown to have significant commercial applications, and now
there are many thousands of civil users of GPS worldwide.
GPS system made of twenty-four satellites circling the Earth every twelve hours at
an altitude of 20,200 km. Each satellite transmits at two frequencies in L-band, at any
time four of these satellites will enable users on the ground to determine their
positions every 100 nanoseconds. The GPS ground antenna has to be circularly
polarized, omni-directional, wide-beam and low gain antenna. When it comes to size,
mass and cost at L-band, the microstrip patch antenna is the best candidate. Ball
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Corporation has produced a dual stacked patch antenna to achieve the required two
L-band frequencies of the GPS system.
1.7.3 Direct Broadcast Satellite System (DBS)
A DBS system has been providing television coverage to public in many countries.
The ground user antenna needs high gain of about 30dBi, circularly polarized, low
axial ratio antenna and operating at the frequency of 12 GHz.
Conventional parabolic reflector antennas can easily meet these specifications.
However, they are rather bulky in size and cannot be installed onto an existing
building.
Performance of reflector antennas degraded due to rain, wind and snow. These led to
development of the micro strip array antennas for DBS. For example, Yagi Antenna
Corporation developed an array with 1024 circular patch elements with a peak gain
of 33dBi. NHK Science and Technical Research Laboratories have developed
several types of mobile DBS receiver for buses, trains, cars and airplanes.
In the case of mobile DBS receivers for cars, a micro strip array antenna with a tilted
beam has been investigated and tested.
1.7.4 Non-satellite based applications
Besides for satellite base applications micro strip antenna also used in many other
areas. In aircraft, micro strip antenna has been used for the purposes of altimetry,
collision avoidance and remote sensing. In medical field, micro strip antenna found
to be useful for medical hyperthermia applications.
In remote sensing, the Synthetic Aperture Radar (SAR) system is used to determine
ground soil grades, vegetation type, ocean wave speed and direction, agriculture