Conductor-backed Tellegen slab as twist polariser

A conductor-backed slab of nonreciprocal bi-isotropic material with nonzero Tellegen parameter is shown to act as a twist polariser (crosspolarising reflector) when the medium parameters of the slab satisfy a certain condition, whence a linearly polarised incident plane wave is reflected as crosspolarised. This effect is seen to be broadbanded for large values and narrowbanded for low values of the Tellegen parameter and the operation is independent of the polarisation direction of the incident wave. Analysis of the Tellegen slab is outlined and the two operating modes for the twist polariser are discussed.