Design of YAGI-UDA Antenna with Improved Radiation Pattern

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Addis Ababa University


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.



Yagi-Uda antenna optimization, gain, front-to-back ratio, voltage stand wave ratio, radiation pattern, Numerical electromagnetic code, Genetic algorithms