Filter-Theory-Based Design of a Quad-Band Linear-to-Circular Polarization Converter for Satcom Applications

A quad-band linear-to-circular polarization converter with low insertion loss is presented for satellite communication (Satcom) applications. Addressing the well-known challenges in designing metasurfaces capable of multi-band operation, a generalized circuit-based synthesis approach, based on classical filter theory, is proposed. The method enables the design of N-band polarization converters by implementing a pair of second-order band-stop frequency-selective surface (FSS) filters for each band. Cascading multiple such layers yields the desired multi-band response. Equivalent circuit parameters are derived from high-level system specifications, such as target center frequencies, and are then mapped to physical dimensions. Full-wave simulations and experimental measurements confirm that the proposed converter achieves polarization conversion across both uplink and downlink sub-bands of the Ku and Ka bands, with right-hand and left-hand circular polarizations (RHCP and LHCP), respectively. These results are achieved while maintaining low levels of insertion loss across all operating bands.