Abstract: A scanning apparatus operable in the microwave, mm-wave, sub mm-wave (Terahertz) and infrared ranges comprises a primary drum (10) mounted for rotation about a central axis A of the primary drum being hollow and of rectangular polygonal form to provide a number of sides or facets (12, 14) each adapted to transmit such radiation, from a field of view, which is plane polarized in a first direction at 45° with respect to the rotary axis of the drum and to reflect radiation which is plane polarized in an orthogonal direction. Thus, radiation passing into the drum though whichever said side of the drum is currently facing the field of view and passing towards the diametrically opposite side will be plane polarized with a polarization direction such as to be reflected back by that diametrically opposite side towards the rotary axis of the drum.

Abstract: Imaging apparatus is disclosed for passive microwave, millimetre wave, sub-millimetre wave or infrared imaging, the apparatus including a receiver (10) for receiving radiation from the scene or subject being imaged, means for directing such radiation onto the receiver, a cold source (16) or a hot source (16), i.e. a source with a low or high black body temperature, and means (14, 14a) for directing the image or shadow of said cold source or hot source onto the scene or subject being imaged. The result is to produce improved contrast in the image obtained.