Ultra-low-noise receivers for the 1 to 120 GHz frequency range

Recent developments in ultra-low-noise receiver technology for frequencies up to 120 GHz are discussed. The following main topics are covered: - a short review of competing low-noise devices, - noise and signal properties of heterostructure field-effect transistors (HFET´s) at cryogenic temperatures, - design and examples of the realization of wideband low-noise, cryogenically-coolable HFET amplifiers in the 1 to 120 GHz range, - examples of HFET receiver realizations and the factors limiting their performance, and - a comparison of competing ultra-low-noise receiver technologies (masers, SIS/HFET IF amplifier tandems) in the 1 to 120 GHz frequency range. Illustrative examples of the different receivers installed on U.S.-based antennas are presented, followed by a short discussion of possible future developments.