New designs of ultra wide-band communication antennas using a genetic algorithm

The paper investigates new designs of loaded wire antennas with broad-band characteristics. A two-step design procedure is proposed for the design. First, different unloaded antennas configurations are examined with a view to identifying candidates that exhibit the lowest voltage standing wave ratio (VSWR) and highest gain characteristics. Multi-armed antennas with straight wire segments that branch off symmetrically from a central stem are found to be excellent potential candidates. Next, the antenna with the best performance is loaded with resonant tank circuits and a matching network is designed. The loads can enhance the antenna characteristics to yield high gain and low VSWR by modifying the current distribution and can force it to radiate nearer to the horizon in the elevation plane with an almost omnidirectional pattern in the azimuth plane. An efficient optimization procedure based on the genetic algorithm is employed to simultaneously determine the load components, their locations, and the parameters of the matching network. Several examples of four- and eight-arm antennas with bandwidth of 7.5:1 and 15:1 illustrate the effectiveness of the design procedure.