NEW DESIGNS OF ULTRA-WIDE-BAND COMMUNICATION ANTENNAS USING A GENETICALGORITHM

The purpose of this paper is to investigate new designs of loaded wire antennas with broad-band characteristics. A two-step design procedure is proposed for the design, First, different unloaded antennas config urations are examined with a view to identifying candidates that exhib it the lowest voltage standing wave ratio (VSWR) and highest gain char acteristics. Multi-armed antennas with straight wire segments that bra nch off symmetrically from a central stem are found to be excellent po tential candidates, Next, the antenna with the best performance is loa ded with resonant tank circuits and a matching network is designed, Th e loads can enhance the antenna characteristics to yield high gain and low VSWR by modifying the current distribution and can force it to ra diate nearer to the horizon in the elevation plane with an almost omni directional pattern in the azimuth plane. An efficient optimization pr ocedure based on the genetic algorithm is employed to simultaneously d etermine the load components, their locations, and the parameters of t he matching network. Several examples of four-and eight-arm antennas w ith bandwidth of 7.5:1 and 15:1 illustrate the effectiveness of the de sign procedure.