Element shape optimization of planar periodic structures

The paper discusses the choice of the element shape in planar periodic structures (frequency selective surfaces and reflectarrays). On the one hand, the element shape mainly determines the performance of the periodic structure (e.g., in terms of bandwidth, cross-polarization level), and, on the other hand, it is strictly related to fabrication issues. The analysis tools, based on the MoM/BI-RME (method of moments/boundary integral-resonant mode expansion) method (which allows for dealing with arbitrarily shaped elements), are briefly presented, and the solutions adopted in some practical cases are reported. With regards to reflectarrays, a novel method, based on a perturbation technique, is outlined and applied to the fast calculation of the phase diagram.