Aberration-free quasi-optical systems

Millimetre-wave/sub-millimetre-wave remote-sensing radiometry is being used for astronomy and for studies of the Earth´s atmosphere and oceans from space-platforms. A radiometer for such a purpose consists of a main reflector antenna coupled to a receiver, or to an imaging array of receivers, via an optical network of focussing reflectors and planar components. The performance specifications for such systems are usually demanding, in particular with regard to the system´s antenna pattern and to very high beam-efficiency which implies low-aberration optics. The paper examines the constraints on the dimensional scale of optical systems that low aberration requires.