Evolutionary Optimization of Quadrifilar Helical and Yagi-Uda Antennas

We present optimization results obtained for two type of antennas using evolutionary algo- rithms. A quadrilar helical UHF antenna is currentlyflying aboard NASA's Mars Odyssey spacecraft and is due to reach nal Martian orbit insertion in January, 2002. Using this antenna as a benchmark, we ran experiments employing a coevolutionary genetic algorithm to evolve a quadrilar helical design in-situ{ i.e., in the presence of a surrounding structure. Results show a 93% improvement at 400 MHz anda48%improvementat438MHzintheaveragegain. Theevolvedantennaisalsoone-fourththesize. Yagi-Uda antennas are known to be dicult to design and optimize due to their sensitivity at high gain and the inclusion of numerous parasitic elements. Our tness calculation allows the implicit relationship between power gain and sidelobe/backlobe loss to emerge naturally, a technique that is less complex than previous approaches. Our results include Yagi-Uda antennas that have excellent bandwidth and gain properties with very good impedance characteristics. Results exceeded previous Yagi-Uda antennas produced via evolutionary algorithms by at least 7.8% in mainlobe gain.

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