Cryogenic, HEMT, low-noise receivers for 1.3 to 43 GHz range

After a review of recent progress in cryogenically cooled high-electron-mobility-transistor (HEMT) devices and amplifiers, a description is given of the construction and performance of a number of receiver front-ends built for radioastronomy applications using very-low-noise HEMT amplifiers and small, closed-cycle 13 K refrigerators. The noise temperature of receivers, measured at the room temperature circular waveguide input (for example, 10.5 K at 8.4 GHz), are only slightly inferior to those of solid-state maser receivers. A summary of the noise performance of all cryogenic front-ends constructed or planned for the very long baseline array (VLBA), comprised of ten 25-m-diameter paraboloidal reflectors each located in a different site within the US, is given.<>