Dielectric Embedded Bandpass FSS Linear to Circular Polarisation Transformers

This paper describes a major advance in the design of bandpass anisotropic frequency selective surfaces (FSS) which are engineered to convert linearly polarized (LP) waves into circularly polarized (CP) signals at normal incidence. The thin metal structure operates in transmission mode and is composed of an array of cross slots with unequal arm lengths in the vertical and horizontal directions. We show that a polarisation converter formed by sandwiching the FSS between two flat PTFE substrates can be designed to give a 3dB axial ratio (AR) bandwidth that is significantly larger than the maximum value previously reported for freestanding topologies. The influence of the two supporting dielectric layers on the passband amplitude shaping and phase responses for TE and TM waves is investigated for various dielectric slab thicknesses. Numerical optimisation is then used to exploit this additional design parameter to create a polarization transformer that exhibits a 3dB AR bandwidth of about 8% at a center working frequency of 10.33 GHz. Spectral transmission measurements in the 8–12 GHz band will be presented at the conference.