Resistive polarisers and quasi-optical planar isolators

In order to construct truly planar quasi-optical isolators it is necessary to develop resistive polarisers, which transmit one linear polarisation and absorb the orthogonal polarisation. We report on two methods of constructing these planar resistive polarisers.

The first method uses a "Venetian blind" structure comprising a parallel array of narrow strips of thin absorbing film placed normal to the beam, for which we have demonstrated <0.2dB insertion loss for E_perpendicular to the absorbing strips and losses up to 40dB for E_parallel. The return losses at normal incidence were >20dB for E_parallel and >30dB for E_perpendicular.

The second method uses a resistive wire grid polariser of a specific impedance per square combined with a metallic grid spaced one quarter wavelength away in a configuration similar to a Salisbury screen. These can be built around quarter wavelength matching layers to allow truly planar isolators to be constructed with thicknesses of a few millimetres. Large area planar isolators (325mm diameter) operating at W-band have achieved 1dB insertion loss, >20dB isolation and >17dB return loss over 75-90GHz.