Circular Polarization Conversion Using Dual Frequency Selective Surfaces for Full-Duplex Satellite Communications

This article proposes an approach to circular polarization conversion using two anisotropic frequency selective surfaces in a frequency-duplex system. We focus on validating the proposed conversion topology from H-polarization to left-hand circular polarization in the forward channel at
$f_{1}$
, and from right-hand circular polarization to V-polarization in the backward channel at
$f_{2}$
, to enable full-duplex satellite communications. The multiconductor transmission line model is employed to characterize the properties of each unit cell and to express the required scattering parameters for each surface at frequencies
$f_{1}$
and
$f_{2}$
. The obtained scattering parameters are then realized using a cascade of two frequency selective surfaces. The first surface features a diagonal strip to convert the incident H-polarized field into its perpendicular V-polarized field at
$f_{1}$
. The second surface, employing a dual-split-ring structure, functions as an anisotropic layer to transform the perpendicular component into circular polarization. Similarly, at
$f_{2}$
, the reverse channel converts an incident right-hand circularly-polarized field into an V-polarized output field. The proposed approach has been validated in the X-band and tested for polarization transformation performance in a full-anechoic chamber. The experimental results demonstrate that each surface and the entire dual-frequency selective surface system effectively operate as a frequency-duplexer which enables simulatenous bidirectional communication with two orthogonal polarizations.