Millimeter and Submillimeterwave Receivers

Various types of receivers can be used for millimeter and submillimeterwave astronomy. The choices are amplifiers or mixer detectors. For the millimeter band, in the past, maser and paramp devices have been successfully used, but in the last few years HEMT amplifiers have proved to be the best option up to about 40 GHz, because they are inexpensive, quite low noise (about 1-2 K/GHz), stable and wideband. However, currently, above ~40 GHz the best performance is obtained from mixer receivers and this review will address that topic only. When used in either interferometers or in single dish spectroscopy, the receivers measure simultaneously the amplitude and phase of the astronomical signal and are therefore fundamentally limited by the quantum noise inherent in the measurement process, which increases linearly with frequency. A receiver which achieves a noise temperature within a factor of 10 of this limit is considered to be well optimized, so that the usual criterion for the noise temperature characterizing a single side-band receiver is that it should be ≲ 10hv/k or equivalently ≲ 0.5 K/GHz.