Patent ID: 7443560

Claim:
A scanning imaging apparatus operable at millimetre wavelengths or thereabouts comprising an optical system, a plurality of receiver elements together forming a receiver array, a processor and a display means, wherein the optical system comprises: a curved polariser/reflector that allows radiation of a first polarisation to pass through, and reflects radiation having a polarisation orthogonal to the first polarisation; a rotatable reflective plate, the reflective plate having an axis of rotation, wherein the axis of rotation is inclined at a non-zero angle θ a to both the reflective plate and the normal to the reflective plate at the centre of rotation, and arranged to reflect radiation onto the polariser/reflector plate; a polarisation rotation plate located between the curved polariser/reflector and the rotatable reflective plate, adapted to perform the action of either: transforming incident linearly polarised radiation to circular polarisation, and vice versa, or to non-reciprocally rotate the plane of polarisation of any radiation passing through by 45 degrees; characterised in that the optical system further includes a convex sub-reflector that acts in combination with the curved polariser/reflector to bring radiation to a focus at an image plane, the sub-reflector providing an increased system focal length.