A broadband photolithographic polariser for millimetre wave applications

Circular polarisers are used to convert linear- into circular-polarisation, and vice versa.This is achieved by introducing a phase-shift of 90° between two orthogonal polarisations passing through the device.These devices can be designed using slabs of birefringent material with the appropriate thicknesses (Quarter-Wave Plates).An interesting alternative solution consists of designing planar metallic grids with sub-wavelength geometries that exhibits different behaviour along two orthogonal axes.In this work we present a broadband dielectrically embedded quasi-optical polariser built using photolithographic techniques.The device was experimentally tested using a Vector Network Analyser working in W-band (75-110 GHz).The presented results are in excellent agreement with finite-element analysis simulations: across a 30% bandwidth the transmission along the two axes and the very flat differential phase-shift are respectively: T C = 0:92, T L= 0:95 and Δ℘LC = 89:3 ± 1:5°.