Design of YAGI-UDA Antenna with Improved Radiation Pattern
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Date
2018-07
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Addis Ababa University
Abstract
Yagi-Uda antenna is used to transmit and receive electromagnetic waves. Yagi-Uda antenna also
used for different applications in wireless communication systems,such as radio and television
broadcasting, point-to-point radio communication, wireless local area network, radar, and space
exploration. The main objective of this thesis is to discuss the design and performance factor of
Yagi-Uda antenna. The design factor include antenna geometry,such as element length,element
spacing and element diameters. The performance includes gain,voltage standing wave ratio, front
to back ratio, impedance and radiation pattern. In this work Yagi-Uda antenna simulation was done
by using Numerical electromagnetic code (NEC),comsol multiphysics and matlab software. The
way of improving antenna performance is based on antenna geometry, such as element length,
element spacing and element diameter. Numerical Electromagnetic Coding (4NEC2) is fast and
efficient that used to simulate antenna parameters, such as voltage standing wave ratio, front-toback
ratio, input impedance, reflection coefficient and gain numerically and graphically with
improved radiation pattern. Whereas comsol multiphysics is used to simulate electromagnetic field
in two, three dimensions and mat lab is used to optimize gain and radiation pattern. Antenna
designed at 100MHz for home television receiver and the performance was simulated conventional
(by varying director length and spacing) and unconventional(by using multi-objective optimization
methode). In the former the result couldnot meet the required solution or optimal solution,therefore
unconventional (optimal design ) would be important to get the optimal solution with high antenna
performance. By using genetic algorithms with multi-objective optimization method the forward
gain maximized and the real part impedance is adjusted to be 50Ω and imaginary part being
different from zero. Finally the result was optimized with optimal element length and element
pacing with element diameters held constant and the number of elements is set at N=4,6 and12
The gain of the designed antenna is compared with the conventional results. The unconventional
design result was 6.74 dBi,9.97dBi and 10.98dBi for N=4,6 and12 respectively which is improved
as compared to the conventional design with results in 6.71dBi,8.32dBi and 9.94dBi respectively,
therefore as the result shows genetic algorithms can be used to increase forward gain for large
number of elements.
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Keywords
Yagi-Uda antenna optimization, gain, front-to-back ratio, voltage stand wave ratio, radiation pattern, Numerical electromagnetic code, Genetic algorithms