Modeling polarization mode coupling in frequency-selective surfaces

An analysis of scattering from frequency-selective surfaces (FSS) is developed that correctly accounts for coupling between scattered polarization modes. This is useful for the design of FSS structures with obliquely incident radiation, such as polarization converters (polarizers) for direct broadcast satellite reception by linearly polarized ground terminal antennas. In the past, the neglect of polarization mode coupling limited the performance range of various FSS structures, such as meander-line polarizers, to near normal incidence where mode coupling is weak. The following analysis shows how a suitable pair of polarization modes can be selected to maintain modal independence. The result is a pair of independent equivalent circuits representing scattering of the two modes, together with mode transformation networks. To illustrate the theory, a four-layer meander-line polarizer is designed for an incident angle of 45° off normal. The resulting axial ratio is measured to be 0.3 dB at 12.45 GHz.