Multiple drum apparatus for high speed scanning of microwave, mm-wave and infrared radiation

Scanning apparatus operable for radiation in the microwave, mm-wave and infrared ranges and comprising a support structure, a primary drum which is mounted in said support structure for rotation relative to the support structure about a central axis of the primary drum, said primary drum being hollow and internally polygonal to provide a plurality of internally presented sides or facets, which are capable of reflecting the radiation concerned, a radiation director disposed to direct radiation emanating from a field of view of the apparatus, being a field of view which is fixed with respect to said supporting structure, as opposed to rotating with the primary drum, onto the internally presented sides or facets of the primary drum, such that in each of a succession of line scanning periods, as herein defined, radiation emanating from part of said field of view is directed onto a said reflective side or facet of the primary drum to be reflected therefrom onto a further receiving assembly comprising a rotating faceted reflector, herein referred to as a secondary drum, arranged to reflect the radiation striking it from the first drum onto a radiation receiver or sensor, the apparatus being so arranged that the radiation from said field of view is focussed onto said radiation receiver or sensor and wherein said secondary drum is arranged to be rotated, about an axis parallel with the rotary axis of the primary drum, in synchronism with the latter, in such a way that, over said scanning periods, radiation from substantially all of a respective said facet of the primary drum, or from substantially all of a predetermined region of such facet, can reach said receiver or sensor via said secondary drum.