On the transmitted beam degradation through FSS in the working band by plane-wave spectrum computation and evaluation

In this paper, we implemented the combination of FDTD (Finite Difference Time Domain) and the plane-wave spectrum (PWS) algorithms, to evaluate beam transmission through frequency selective surface (FSS) in the near field region. The hybrid method takes advantage of the FDTD for the wideband analysis ability, and that of the PWS theory in the rapid recomposition for transmitted fields due to variable beam incidence. Consequently, it meets the need of beam transmission evaluation in the working band when the FSS is located among a serial of components, as in a millimeter Quasi-Optical (QO) instrument. After verifying the hybrid approach by results of other methods, we studied the degradations in the transmitted beams through an FSS design within the band of interest. The investigations are performed at the view of the transmission coefficient distributions in the PWS. It is found that the transmitted beam distortion is due to the non-flatness of the transmission coefficient distribution in the spectrum region covered by the beam incidence.