Three-dimensional monolithic frequency selective structure with dielectric loading

Three-dimensional (3-D) frequency selective structure (FSS) is a recent development, which consists of a two-dimensional (2-D) periodic array of monolithic cavities. Number of propagating modes in a cavity and their coupling with air is controlled to obtain a desired quasi-elliptic filtering response. In this paper, we model and examine the effect of placing an external dielectric layer on this new class of FSSs. It is noted that an external thin dielectric layer can significantly modify the frequency response of a 3-D FSS, and hence the dielectric layer may be included as a non-resonating node during the design process, which in turn gives more flexibility in obtaining a desirable symmetric/asymmetric filtering response. We use an efficient full-wave mode-matching method for the present study, and our results are in good agreement with those obtained from measurements.