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A singular characteristic of single-layer frequency selective surface with the element optimized by GA

We have developed multiband single-layer frequency selective surfaces (FSS) by using the optimization technique based on the genetic algorithm (GA). In the frequency responses of these FSS for oblique incidence, unwanted sharp dips appear, depending on the element shape. Similar singular characteristics have been confirmed for a dipole element with the length of a wavelength. But the mechanism causing such singular characteristics has not been investigated for the FSS with the complicated element shape produced by the optimization technique. This paper makes it clear how the singular characteristics of the FSS occur in the frequency response. Firstly, we show briefly the methods for finding the singular frequency with unwanted sharp dips, and also the resonant frequency yielding the specified reflection. Then, by using an example of the FSS developed by us, we explain the mechanism of the singular characteristics from the current distribution. Finally, the validity of the discussion is proved experimentally.