| 摘要 |
Scanning apparatus which may be used in a real-time passive millimetre wavelength imaging system or in other radiometry systems. The apparatus scans input radiation from a scene and output radiation is transmitted to a receiver system, for example a millimetre wave imaging camera or a radar receiver. The apparatus comprises a rotatable reflective plate having an axis of rotation passing through the centre of its surface, secondary reflection means and static reflection means, wherein the secondary reflection means is a second rotatable reflective plate having a common axis of rotation with the first rotatable reflective plate, wherein the common axis of rotation is inclined at a non-zero angle theta b to the normal to the second reflective plate. The normal to the first rotatable plate is inclined at a small angle to the common axis of rotation, typically a few degrees. In a preferred embodiment, the first rotatable reflective plate also forms the secondary reflection means. The static reflection means may be a polarising roof reflector through which radiation is input to and output from the apparatus. In this configuration, the apparatus also includes a 45 DEG Faraday rotator or a birefringent surface such as a Meander-line. An additional Faraday rotator and an inclined polariser may be included in the apparatus and arranged such that radiation output to the receiver system may be separated from the path of input radiation. Alternatively, the scanning apparatus may include a reflector lens arrangement, such that focused output radiation may be output directly to the receiver system. The invention also relates to a reflector lens comprising a first polarising surface, for selectively transmitting and selectively reflecting radiation having a particular direction of polarisation, a second surface for rotating the direction of polarisation of radiation through substantially 45 DEG and a third polarising surface for selectively reflecting and selectively transmitting radiation, wherein the polarisation axis of the third surface makes an angle of substantially 45 DEG with the polarisation axis of the first surface.
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