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 <0.2 dB insertion loss for E.perpendicular to the absorbing strips and losses up to 40 dB for E.parallel. The return losses at normal incidence were >20 dB 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 (325 mm diameter) operating at W-band have achieved 1 dB insertion loss, >20 dB isolation and >17 dB return loss over 75- 90 GHz.