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.