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Designing of Microstrip Patch Antenna
For 3G-WCDMA ApplicationsNeha Chavda#1, Dr. Vedvyas Dwivedi#2,
Dr. Kiran Parmar#3
1M.E. Student, EC Department, L.D.college of Engineering,
Ahmedabad, Gujarat, India2Director, Noble Group of Institutions,
Junagadh, Gujarat, India
3Professor, EC Department, L.D.college of Engineering,
Ahmedabad, Gujarat, [email protected]
[email protected]
[email protected]
Abstract Mobile communication in various flavours
has seen a tremendous growth during the last decade. 3G
mobile system is working on standard UMTS (1920-2170
MHz). The most common form of UMTS uses WCDMA
as the underlying air interface. The bands between 1920-
1980 MHz and 2110-2170 MHz have been allocated asthe uplink and
downlink frequency bands of FDD
frequency bands respectively for 3G mobile radio
systems.The microstrip patch antennas are increasing in
popularity for use in wireless applications due to their
low-profile structure. Microstrip patch antennas have
several well-known advantages, such as low cost, light
weight and ease of fabrication. The objective of the
paper is to develop a compact and broadband microstrip
patch antenna for 3G mobile communication system.
Simulation of proposed design gives results which are
very nearer to predefined attributes and parameters.
KeywordsPatch Antenna, Feeding Technique
INTRODUCTION
Wireless communication has been developed
rapidly and it has a dramatic impact on human life.The current
trend in commercial and government
communication systems has been to develop low cost,minimal
weight, low profile antennas that are capable
of maintaining high performance over a largespectrum of
frequencies. The wireless communication
has enjoyed explosive growth over the past decade. Asdemands for
increased capacity and quality grow,
improved methods for harnessing the multipath
wireless channel must be developed. The air interfaceof 3G
systems is WCDMA, which offers increasedcapacity and supports
variable data rates. This
technological trend has focused much effort into thedesign of
Microstrip (patch) antennas. As electronic
devices continue to shrink in size, the antennadesigner is
pushed to reduce the antenna size as well.
With a simple geometry, patch antennas offer manyadvantages not
commonly exhibited in other antenna
configurations. For example, they are extremely low
profile, lightweight, simple and inexpensive tofabricate using
modern day printed circuit board
technology, compatible with microwave and
millimeter-wave integrated circuits, and have theability to
conform to planar and non planar surfaces.
A microstrip patch antenna also has very desirable
mechanical properties. It can withstand tremendous
shock and vibration. Because the antenna is on a solidsubstrate,
the patch cannot flex, and small changes in
the substrate thickness have only a minor effect on the
resonant frequency.
EQUATIONSFORGEOMETRYOF PATCH ANTENNA
Conventional Microstrip antennas consist of a pair
of parallel conducting layers separating a dielectricmedium,
referred as substrate. In this configuration,
the upper conducting layer or patch is the source of
radiation where electromagnetic energy fringes off theedges of
the patch and into the substrate. The lower
conducting layer acts as a perfectly reflecting ground
plane, bouncing energy back through the substrate andinto free
space. Microstrip antenna should be designed
so that its maximum wave pattern is normal to thepatch. This is
accomplished by proper choice of mode
of excitation beneath the patch. Generally, patch ofMicrostrip
antenna thickness is very thin in the range
of t
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The relationship of width (W) height (h) effective
dielectric constant reff, and relative dielectric constant
of the substrate rare related as follow [2][3].
A very popular and practical approximation
relation for normalized extension of the length is
obtained from below equation. [4][3].
Since the effective length of the patch has beenextended by L on
each side, the effective length of
the patch is expressed as
After analyzing and determining the physicalnature of the
Microstrip antenna it is possible to
design rectangular microstrip antenna dimension,width Wand
LengthL, of patch as follow. [5]
The transmission line model is applicable to
infinite ground planes only. However, for
practicalconsiderations, it is essential to have a finite
groundplane. It has been found that similar results for finite
and infinite ground plane can be obtained if the size ofthe
ground plane is greater than the patch dimensions
by approximately six times the substrate thickness all
around the periphery. Hence, for this design, theground plane
dimensions would be given as
From all above equations the proposed microstrip
patch antenna is designed.
ANTENNA DESIGN
In the typical design procedure of the Microstrip
antenna, the desired resonant frequency, thickness anddielectric
constant of the substrate are known or
selected initially. It is found that the radiating patch ofthe
microstrip antenna has a resonant length
approximately proportional to , and the use of a
microwave substrate with a larger permittivity thus
can result in a small physical antenna length at a
fixedoperating frequency. Comparative table is given
below. Here Operating frequency and height ofsubstrate are fixed
respectively at 2GHz and 0.4 cm.
This result suggests that an antenna size reductionas large as
about 90% can be obtained if the design
with higher value of r is used instead of lower value
of dielectric constant r.
rMaterial
L
(in cm)
W
(in cm)
2.1 Teflon 4.93 6.02
3.2 Taconic_TLC 4.02 5.17
4.4 FR4_epoxy 3.44 4.56
5.7 Mica 3.02 4.09
6.15 Rogers R03006 2.90 3.96
7 Silicon_nitrate 2.72 3.75
8.3 Marble 2.49 3.47
9.2 Alumina_92pct 2.36 3.32
10 Sapphire 2.26 3.1911.9 Silicon 2.06 2.95
12.9 Gallium_arsenide 1.98 2.84
16.5 Diamond 1.73 2.53
Table 1 comparison of patch dimensions for different
materials
This result suggests that an antenna size reduction
as large as about 90% can be obtained if the design
with higher value of r is used instead of lower value
of dielectric constant r.
In this proposed design of rectangular microstrip
antenna, FR4_epoxy dielectric material with r=4.4and dielectric
loss tangent of 0.02 is selected as thesubstrate with 4 mm height.
Then, a patch antenna thatoperates at the specified operating
frequency f0= 2
GHz can be designed by above equations. The antenna
is existed by the coaxial feed away from the center ofthe
patch.
The Coaxial feed or probe feed is a very commontechnique used
for feeding Microstrip patch antennas.
As seen from Fig. 1 the inner conductor of the coaxial
connector extends through the dielectric and issoldered to the
radiating patch, while the outer
conductor is connected to the ground plane. The mainadvantage of
this type of feeding scheme is that the
feed can be placed at any desired location inside thepatch in
order to match with its input impedance. This
feed method is easy to fabricate and has low spuriousradiation.
Also, for thicker substrates, the increased
probe length makes the input impedance moreinductive, leading to
matching problems [6].
Frequency of operation 2 GHz
Dielectric constant 4.4
Height of substrate 0.4 cm
Feeding Method Coaxial feeding
Width of patch 4.56 cm
Length of patch 3.44 cm
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Width of Ground Plane 6.96 cm
Length of Ground Plane 5.84 cm
Table 2 calculated Dimensions for microstrip patch antenna
The feed point is located at that point on the patch,
where the input impedance is 50 ohms for the resonantfrequency.
Hence, a trial and error method is used to
locate the feed point. For different locations of thefeed point,
the return loss is compared and that feed
point is selected where the return loss is mostnegative.
Fig. 1 Design of Rectangular Patch Antenna
SIMULATIONAND RESULT
The practical measurements of the prototypes to
collect the data for calculation of performance havebeen done
for both far-field pattern and S parameters.
The software used to model and simulate the
microstrip patch antenna is Ansoft HFSS software.HFSS is a high
performance full wave electromagnetic
field simulator for arbitrary 3D volumetric passivedevice
modeling. It can be used to calculate and plot
the Sparameters, VSWR as well as the radiationpatterns. The
whole model is scaled down by 0.94 to
get the better results. An evaluation version of thesoftware was
used to obtain the results for this paper.
The bandwidth can be calculated from the return lossplot. The
bandwidth of the antenna can be said to be
those range of frequencies over which the return lossis greater
than -10 dB. -10 dB corresponds to a VSWR
of 2 which is an acceptable figure. The bandwidth ofthe antenna
is calculated (as shown below in Fig. 2) to
be 8 MHz and a center frequency of 2.01 GHz isobtained which is
very close to the desired design
frequency of 2 GHz.
1.00 1.50 2.00 2.50 3.00 3.50 4.00Freq [GHz]
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
dB
(St(pin_
T1,p
in_
T1))
Ansoft Corporation HFSSDesign1XY Plot 1
Curve Info max min
dB(St(pin_T1,pin_T1))
Setup1 : Sweep1-0.0922 -28.8448
Fig. 2 Return Loss of Patch Antenna
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Fig. 3 VSWR plot
Fig. 4 Radiation patterns
Radiation Pattern1. rETotal Radiation Pattern 2. Gain Radiation
Pattern 3.Directivity Radiation Pattern 4.Axial Ratio
1.00 1.50 2.00 2.50 3.00 3.50 4.00Freq [GHz]
0.00
50.00
100.00
150.00
200.00
Ansoft Corporation HFSSDesign1XY Plot 5
Curve Info max min
VSWRt(pin_T1)
Setup1 : Sweep1188.3585 1.0749
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Fig. 5 Smith chart
SUMMERY
The optimization of the Microstrip Patch is
partially realized which concludes that proposed patchantenna
functioning correctly. Important antenna
parameters can be observed from the results which aretabulated
below.
Gain 3.52 dB
Directivity 5.40 dB
VSWR 1.07
Axial Ratio 62.22
Front to Back Ratio 56.16
Table 3 Results
The future scope of work revolves slotting of
antenna to miniaturize the size of antenna. Theinvestigation has
been limited mostly to theoretical
study due to lack of distributive computing platform.Detailed
experimental studies can be taken up at a
later stage to find out a design procedure for slottinginto the
patch. .
REFERENCES
[1] R. Garg,I.J. Bahl, P.Bhartia and A. Ittipiboon,
Microstrip
antenna Design Hand Book, Artech House, Dedham, MA,
2000.
[2] C.A. Balanis, Advanced Engineering Electromagnetics,
John
Wiley & sons, New york, 1989.
[3] Robinson and Y. Rahmat-Samii, "Particle Swarm
Optimization in Electromagnetic". IEEE Transaction on
antennas and propagation, vol. 52, no. 2, pages 397-407,
February 2004.
[4] E.O. Hammerstad, Equations for microstip Circuit Design,
Pro. Fifth European Microwave Conference, page 268-272,
1975.
[5] R. Garg,I.J. Bahl, P.Bhartia and A. Ittipiboon,
Microstripantenna Design Hand Book, Artech House, Dedham, MA,
2000.
[6] S. Maci, G. Biffi Gentili, G. Avitabile, Single-Layer
Dual-
Frequency Patch Antenna, Electronics Letters, 29, 16,
August 1993.
Neha K. Chavda has obtained her bachelor degree in
EC field from VVP, Rajkot, Gujarat. Currently she ispursuing her
master degree in Communication System
Engineering, from L.D. college of Engineering,
Gujarat, INDIA.
Dr. Vedvyas Dwivedi is director of noble group of
institutions, Junagadh. He has wide experience of 15years in
academic field. His area of interest isElectromagnetic, microwave,
radar and antenna.
Dr. Kiran Parmar has been working as Professor at
L.D.college of Engineering, Ahmedabad, since 1995.His area of
interest is satellite and mobile
communication.
