HALF-WAVE PARABOLIC

REFLECTOR ANTENNA

OPTIMIZATION

Parker Singletary, Carson Smith

Advisor: Dr. Gregory J. Mazzaro

Department of Electrical & Computer Engineering

The Citadel, The Military College of South Carolina

171 Moultrie St., Charleston, SC 29409 September 2015

PROJECT GOALS Design, in simulation, a UHF antenna producing maximum power-

on-target, directly in front of the antenna, at a given distance

Minimal power reflection into feeder line

Optimize antenna parameters by using FEKO, a method-of-

moments-based electromagnetic field solver, to vary its physical

dimensions

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PROJECT INSPIRATION U.S. Military Active Denial System (ADS)

95 GHz directed energy beam used for non-lethal crowd dispersal

Heats molecules in the top layers of target’s skin

Interested in the high directivity aspects of the parabolic reflector antenna and wanted to learn more about its applications

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OUR APPROACH Budget, fabrication, and instrumentation constraints

led us to choose a half-wave-dipole reflector antenna

Chose a frequency of 480 MHz so that a physical model could be built and tested on the our school’s campus

Chose a 0.3-meter dipole to make impedance “real” at center frequency (ldipole=0.48λ)

In simulation, vary the radius and depth of the reflector using the ‘grid’ solving method in FEKO to yield high directivity and gain while minimizing VSWR

Verify simulated design with open-air measurements

30 cm dipole used for signal reception

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GAIN OPTIMIZATION RESULTS Varied the parabola radius between 25-35 cm and depth

between 10-35 cm in 100 simulations

Gain peaked when the half-wave dipole was located at the focal parameter location of the dipole

Larger reflectors yielded higher gain values

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Antenna parabola radius corresponding to run number

Antenna parabola depth corresponding to run number

Gain corresponding to run number

“run” = simulation iteration

VSWR OPTIMIZATION RESULTS VSWR was lowest when the dipole was located at the focus of

the antenna

Larger reflectors yielded lower VSWR values

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Antenna parabola radius corresponding to run number

Antenna parabola depth corresponding to run number

VSWR corresponding to run number

SELECTED MODEL Although simulation run 95 yielded the most optimal results, we

selected run 75, so the implemented antenna would not be too

large to handle during testing

In size range, chose model with high gain (8 dB) and reasonable

VSWR (2.5)

Determined parabola’s equation for fabrication

Depth = 23 cm

Radius = 33 cm

Y=0.02112029x2

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IMPLEMENTED MODEL Frame – 2x2 and 2x4 pine

Reflector – Aluminum roofing flashing

Dipole – Stripped 14 gauge residential wire

Dipole support – ½ inch PVC

Feedline – Coaxial cable with BNC connector

Reflector supports were placed according to the

parabola’s equation

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RADIATION PATTERN AND BEAMWIDTH TEST Connected implemented antenna to

function generator producing a 1 mW constant sinusoid at 480 MHz

Utilized second dipole as a receiver connected to a spectrum analyzer for measurements

Placed second dipole at a distance of 50 feet from transmitting antenna (~20λ) and measured the average power received along a 180° swath at 5° intervals

Determined that the antenna has a 40° 3-dB beamwidth

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0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Po

we

r R

ec

eiv

ed

(d

Bm

)

Azimuth (degrees)

Received Power vs. Angle

Received Power vs. Angle 3 dB down

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BANDWIDTH TEST Test performed at 90° azimuth

Transmission frequency varied between

400 MHz and 500 MHz in 5 MHz intervals

Test results showed the center frequency was closer to 450 MHz, much

lower than designed

3-dB bandwidth of 75 MHz

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400 420 440 460 480 500

Po

we

r R

ec

eiv

ed

(d

Bm

)

Frequency (MHz)

Received Power vs. Frequency

Received Power vs. Frequency 3dB down

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COMPARISON OF RESULTS Experimental gain pattern tracked

theoretical gain pattern within 1dBm

Performed curve fitting in Excel with a

4th-order polynomial to smooth

measured data, for a clearer

comparison against simulated results

Testing methods likely induced much of

the error (e.g. multipath, including ground bounce between Tx and Rx)

Tests were performed on a large field as

an anechoic chamber was unavailable

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1.00

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0 50 100 150

Ga

in (

dB

m)

Angle (Degrees)

Theoretical vs. Experimental Gain

Theoretical GainExperimental GainPoly. (Experimental Gain)

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CONCLUSIONS We were able to successfully design, simulate, and

build an optimized half-wave dipole reflector antenna

Simulation results showed clear tradeoffs between VSWR and gain when manipulating reflector geometry

Larger parabola radii resulted in more desirable gain and VSWR while depth variation yielded more contrasting output parameters, so parabola depth drove the design

The antenna’s operating frequency enables it be used for a variety of applications at low RF power, potentially in a secure point-to-point RF link or an RF device jammer

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ACKNOWLEDGEMENTS

Department of Electrical & Computer

Engineering at The Citadel

Dr. Gregory J. Mazzaro, Advisor

Altair, FEKO software provider

Applied EM, Inc. (Hampton, VA)

Dr. C. J. Reddy

Thomas G. Campbell, Sr. 13

Singletary, Smith, Mazzaro