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

Shafaqkausar786@yahoo.com, aumer313@gmail.com, hamood@ceme.nust.edu.pk,tayyabhassanamer@gmail.com

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

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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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