On the Transmitted Beam Shift Through FSS Structure by Phase Analysis

The frequency selective surfaces (FSSs) are the vital components in multiband quasi-optical (QO) feed instruments for reflector antennas. Designers of QO use FSSs to combine beams in different frequency bands onto a shared feeding aperture. However, the FSSs will shift the transmitted beam, and that brings difficulties in the design and fabrication process of an QO instrument. In this letter, we report a simple and efficient method to predict the transmitted beam shift caused by FSSs. It is based on the phase analysis of the plane-wave transmission functions of FSSs within a range of incident angles. For an FSS design, the transmitted beam shift is predicted by the proposed method, and then verified based on the transmitted field distributions calculated by the plane-wave spectrum method. As shown in this letter, the advantages of the proposed method include briefness in concept and simplicity in implementation.