Circuital Analysis of Full-Metal Polarisers Based on 3D Unit-Cells

Polarising screens based on the use of fully metallic three-dimensional unit-cells are here reported. Two type of cells are proposed to build the doubly-periodic architecture, the second one allowing for an extended axial-ratio bandwidth. Both unit-cells are based on the use of metallic waveguide sections operating well below cutoff. In spite of being reactive, total transmission through the cells is possible thanks to the perforation of several resonators in the structure. These perforations allow, additionally, to tune the phase of the outgoing wave and to generate a circularly polarised signal from a 45° -slant linearly polarised impinging one. Equivalent circuit models are proposed in each case to understand the cells behavior and to help in the design of two polarisers operating around 20 GHz and providing good axial-ratio performance.