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Smart Adaptive Beam Forming Antenna for Interference Minimization
Ahmed Kausar, Hamood ur Rahman,Shafaq Kausar, Tayyab Hassan
Department of Electrical Engineering
NUST College of Electrical and Mechanical Engineering
National University of Science & Technology, Islamabad Pakistan
[email protected], [email protected], [email protected],[email protected]
Abstract - ESPAR antenna steers beam by variation of reactive
impedances, here we have simulated & later designed hardware
for steering beam in direction of desired maxima and placement
of null towards maximum interference. Antenna is simulated in
HFSS version 12, only center element is active which is
surrounded by array of six parasitic elements loaded with
varactor. Hardware results were measured in anechoic chamber
and 8 dB gain was achieved in specified direction for theta & phi
and step size achieved was 30 degree.
Keywords—ESPAR (Electronically Steerable Parasitic Array
Radiator), Anechoic Chamber, Beam Steering, Adaptive Beam
Forming, Parasitic Element
I. INTRODUCTION
Smart antenna is an antenna that has signal processing
capability to transmit and receive in an adaptive and spatially
sensitive manner. Adaptive beam forming would considerably
improve gain in desired direction subsequently low transmit
power will be required for maintaining EIRP (Equivalent
Isotropically Radiated Power. Smart antennas can improve
user experience and system capacity by reducing interference,
extending range, increasing data rates, and improving quality.
Generally there are two types of beam steering, Electronic
beam steering and mechanical beam steering. Electronic beam
steering is more robust and reliable since it does not involve
moving parts. The Electronically Steerable Passive Array
Radiator (ESPAR) an antenna that suits application in ad hoc
computer networks. Wireless ad hoc networks are a solution
comparable to wired systems in terms of quality and are
relatively low cost. Wireless systems are susceptible
interference and interference may degrade the SNR (Signal to
Noise Ratio) [1]
. In case of low gain antenna to overcome
interference one has to operate at high transmission power for
maintain considerable SNR, ESPAR antenna can overcome
this problem by placement of maxima in direction of desired
signal and minima in direction of maximum interference. In
wireless communications systems, interference becomes
a dominant factor in limiting quality and capacity. ESPAR
antenna overcomes this limitation thus both quality and
capacity of channel is increased.
II. STATE OF THE ART
We have designed adaptive beam forming smart antenna
that can automatically steers beam toward active source, such
antenna will always be pointing towards source no matter
source is moving or stationary. Such antenna is likely to
revolutionize present day communication systems since
instead of uni-directional / omni-directional antennas of cell
phones, laptops, radio sets etc directional antenna would be
used. We are exploiting mutual coupling phenomena between
antenna elements by induction of mutual coupling phenomena
antenna size is reduced so great extent thereby reducing cost.
Such antenna is likely to revolutionize all present day
communications systems and RF planning by introducing
“directionality” which is presently not the case because of
large size and higher cost of directional antennas. Our
proposed designed caters for these two bottlenecks therefore
advancement in our product would have greater impact
towards green technology, reduced radiations, increased
battery life, minimization of interferences and multiple use of
same spectrum.
We have achieved wireless communication at reduced
transmitted powers & minimum interference levels thus
maximizing channel capacity. In present day communication
systems onmi-directional and uni-directional antennas are
used because of two factors.
• Low cost
• Reduced Size
We have developed directional antenna overcoming above
mentioned bottlenecks by virtue of mutual coupling
phenomena thus it’s a new step forward towards
advancement in smart antennas and their usage.
III. LOADING OF PARASITIC ELEMENTS
Elements 1-6 are parasitic elements and only these are
loaded with adjustable reactance, where as element 0 is the
only active elements (Figure 1). Feed is applied to centre
element only this provides lesser complexity and compact size
compared to traditional Phased Array Antenna [2]
. In ESPAR
Antenna Beam is steered by varying reactance of parasitic
elements in whereas in Phased Array Antennas Beam is
steered by varying phase of impinging electric field.
978-1-4799-2975-7/13/$31.00 ©2013 IEEE 6
Figure1: Variable directionality achieved
For achievement of directionality phase shifter antennas are
used each element in phase shift antenna has a feed thus loses
are there at feed elements moreover size cannot be reduced
after certain limit because of the fact that once elements are
placed closer to each other mutual coupling phenomena takes
into account(Figure 2)��
�
Figure 2: Active centre feed
� �
Figure 3: Active centre feed
IV. MECHANICAL DESIGN
Seven monopoles are placed on cylindrical skirt, this skirt
structure provides mechanically sound structure for housing of
antenna control circuitry [4], shielding them from RF external
sources.
Figure 4: Hardware Prototype
Monopoles are made of copper wire with diameter of
lambda / 200 and ground skirt is made of aluminum, ground
skirt reflects electromagnetic waves and keeps elevation angle
closer to 90 degrees and reduces elevated beam pattern.
V. CONTROL CIRCUITRY
Analog devices RF switch ADG 904 is used for opening
and shortening. Once set of parasitic monopoles is shorted
with ground plane there is minimum inductive effect and beam
is formed in opposite direction. By opening and shortening of
parasitic elements along circular array beam is steered in steps
of 360 degree. Following table depicts placement of maxima
in accordance with status of RF switch of each parasitic
monopole.
Element
# Status
Beam at
60
Degree
Status
Beam at
120
Degree
Status
Beam at
180
Degree
1 Short Short Short
2 Open� Short� Short�
3 Short� Open� Short�
4 Short� Short� Open�
5 Short� Short� Short�
6 Short Open Short
Table I
�����PCB board was designed in Diptrace (Figure 5) for opening
and shortening of respective parasitic monopoles.ADG 904 is
4:1 multiplexer RF switch, opening and shorting is governed
by DC voltage.
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Figure 5: RF PCB
VI. HFSS SIMULATIONS
Antenna was modeled in HFSS version 12 and parasitic
elements were loaded by different values using lumped port
excitation [3] and loading with different values of inductances
and capacitances thereby yielding different impedance values
Figure 6: HFSS Simulated model
VI. HARDWARE RESULTS
Anechoic chamber signed antenna system performance was
measured is Anechoic Chamber and actual results were cent
percent compliant with simulation. 8 dB gain was achieved for
�=90 and �=0, 30, 45 degree respectively.
Anechoic Chamber results for Figure 7 depicts maxima is
attained almost at 90 degrees from z- Axis (Elevation angle is
90 degrees)
�
Figure 7: Elevation Plot �=90
Element # 2-6 is shorted and Element # 1 opened, beam is
formed at �=0 degree (Figure: 8)
Figure 8: Azimuth Plot �=0
Element # 1,4,5 & 6 are shorted and Element # 2 & 3 are
opened, beam is formed at �=30 degree (Figure: 9)
,
Figure 9: Azimuth Plot �=30
Element # 1,3, 4, 5 & 6 are shorted and Element # 2 is
opened, beam is formed at �=55 degree (Figure: 10)
Figure10: Azimuth Plot �=55
VII. CONCLUSIONS
EPAR antenna is first simulated in HFSS and then hardware
is designed, beam steering was achieved by opening and
shortening of parasitic elements, Vc (control voltage) regulate
opening and shortening thereby steering beam.
Simulation results shows 3 D pattern of beam and verifies
that maxima or minima can be placed in any desired direction
along azimuth. Towards direction of maximum interference
8
minima is placed so that channel capacity can be increased by
reducing interference levels.
Gain of 8dB was achieved in specified directions of theta
(�) and phi (�). Plots from anechoic chamber show that
results are complaint with simulations. Prototype is there for
developed that can place null in direction of maximum
interference and maxima in direction of desired signal.
REFERENCES
[1] Y. Ozaki, J. Ozawa, E. Taillefer, J. Cheng ,and Y. Watanabe A Simple DOA Estimator Using Adjacent Pattern Power Ratio With Switched
Beam Antenna, Progress In Electromagnetics Research C, Vol. 22,pages 55-71, 2011
[2] A. Mitilineos, Konstantinos S. Mougiakos, and Stelios C. A.
Thomopoulos Design and Optimization of ESPAR Antennas via Impedance Measurements and a Genetic Algorithm, IEEE Antennas propogation mag, vol. 51, no. 2, pages. 118-123, 2009
[3] Takashi Ohira and Kyouichi Iigusa, Electronically Steerable Parasitic Array Radiator Antenna, Electronics & communication in Japan (Part
II),Volume 87, issue 10, pages 25-45 ,2004
[4] Constantine A. Balanis, Antenna Theory: Analysis and Design
[5] Tayyab Hassan, Ahmed Kausar, Hassan Umair and Mhammad Anis
Gain Optimization of Seven Element ESPAR Antenna using Quasi-Netwon Method, IEEE research paper published in Microwave Technology & Computational Electromagnetics (ICMTCE), 2011 IEEE
International Conference, pages 293 – 296, May 2011
�
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