A new subdomain basis-function model for the concentric (and single) ring element in FSS arrays

Doubly periodic arrays of concentric and single rings have found applications as quasi-optical diplexers in the millimetric and other frequency bands. We address issues related to the modelling accuracy and the efficiency of computations. We present a new model for the ring element (single or concentric) that is able to predict the RF performance of the array of such elements more accurately than the entire domain method and is also more efficient than the existing subdomain models. The mathematical models for frequency selective surfaces rely on the truncation of the infinite processes to manageable limits. Consequently, the accuracy of the RF performance prediction of an FSS structure is dependent on the number of terms in the truncated series (or the number of iterations in the truncated process). An example is shown for the entire domain method, where the computed value of the resonance frequency of the structure varies with the number of Floquet modes used. Evidently, the lack of convergence with increased Floquet modes reduces the application reliability of this model, particularly for single FSS screens. The subdomain method can provide a more accurate prediction of the RF performance which converges to the measured RF values as the number of terms is increased. The existing subdomain models, however, require much longer computation times than the entire-domain models. We propose a new subdomain model which significantly reduces the computation time