Polygon subdomain basis-function model for the ring element in FSS arrays

An efficient subdomain approach is presented which can predict the frequency response of ring-element frequency-selective surfaces (FSS) more accurately than existing entire-domain models. The integral equation for the unknown fields (or currents) on the frequency-selective surface is used for the mathematical model, and the elements are approximated by two mutually rotated polygons. Roof-top basis functions are used on each polygon chord to represent the unknown fields (or currents). This method offers a significant improvement in computational efficiency when compared with other subdomain methods that have been reported. This is achieved by using far fewer subsections, thus reducing the number of unknowns to be determined. Numerical results for several FSS geometries are compared with those obtained using the entire-domain model and measurements, to demonstrate that this technique offers high reliability as a design tool, particularly for single-screen FSS structures.