Submillimeter receivers for radio astronomy

The state of development of receivers for submillimeter-wave radio astronomy is reviewed. Bolometers for continuum observation, hot-electron mixer receivers for narrowband spectral line observation, and heterodyne receivers, both Schottky diode and superconducting tunnel junction, are presented. At the lower frequency end of the submillimeter band, standard waveguide techniques, scaled from millimeter wavelengths, prevail. At wavelengths shorter than about 0.5 mm, quasioptical designs are preferred. In the case of Schottky diode receivers, corner cube designs are used almost exclusively, whereas integrated mixer designs are the focal point of research for superconductor-insulator-superconductor (SIS) receivers at these wavelengths. Although such designs are extensively reviewed, it is nevertheless the Schottky diode mixer remains the element of choice at the shortest submillimeter wavelengths