The recent development of many new ultra-wideband (UWB) array technologies has created a demand for antenna elements that can effectively operate over similar bandwidths. For example, the polyfractal [1] and RPS [2] topologies are capable of exhibiting remarkably wide frequency bandwidths on the order Of 20:1, 40:1 or even more, depending on the array size. Often, the antenna elements that are capable of these extended bandwidths begin to develop several lobes in the radiation pattern and generate increased cross-polarized radiation at their upper range of operating frequencies. A new type of ultra-wideband antenna has been developed based on a spline-shaping technique and a particle swarm algorithm (PSO) [3]. With proper attention to the radiation pattern, cross-polarization, and return loss in the PSO cost function, this method is capable of producing UWB antenna elements that minimize all the aforementioned undesirable characteristics, making them very suitable for use in UWB array systems. with bandwidths up to 4:1 and perhaps even wider.
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