New designs of ultra-broadband antennas using a genetic algorithm

There has been a growing interest in wire antennas loaded with resonant traps, i.e, RLC circuits, because of their low profile and broadband characteristics. The wide bandwidth which can be 15:1 or greater, allows frequency hopping without electronic switching, and the use of simultaneous transmit-receive modes of operation. Typically, the structure consists of one or more wire segments that are loaded with parallel RLC circuits, and a single matching network at the feed point. The genetic algorithm (GA) was used to develop a numerically efficient procedure for designing these antennas and was employed for broadband monopole, twin whip, and folded monopole type of antennas. In these designs, the GA was used to optimize the RLC loads, then locations, and the parameters of the matching network. The GA efficiently optimizes all the parameters of the system simultaneously, using only a moderate amount of CPU time. It evaluates a large number of antenna designs that are developed through evolution, and gradually improves them with respect to the objective function. The objective function is related, in turn, to the quantities we wish to optimize, e.g., the system gain and VSWR. The paper presents some new loaded wire antenna designs, with improved broadband characteristics than those previously reported in the literature. The antennas comprise of four identical loaded wire arms which branch off of a central stem. Two examples of such configurations, viz., the "diamond" and the "kite" antennas are depicted.