Multilayer aperture ring frequency selective surface modelling

This paper describes the design of a low loss quasi-optical beam splitter, which is required to provide efficient diplexing of the bands 316.5-325.5 GHz and 349.5-358.5 GHz with at least 20 dB of isolation. To minimise the filter insertion loss, frequency selective surfaces (FSS) that consists of freestanding resonant shorted ring elements is proposed. In addition, to achieve the stringent isolation a two layer FSS structure is required. Two commercial electromagnetic modelling tools, a time domain finite integral method (FIT) and a finite element method (FEM) solver are used to obtain the specified transmission response. The FIT solver was used to generate fast design information at normal incidence while the FEM was only used to obtain the final design of the FSS at 45° due to its substantially increased run times.