Low Noise SIS Mixers and Cryogenic Amplifiers for Sub-Millimeter Astronomy

Sammanfattning: This PhD thesis presents the work that was done developing radioastronomy instrumentation. The first part of this work deals with 2-stage low-noise cryogenic amplifiers using commercial GaAs HEMT transistors for frequency bnads: 3.4-4.6 GHz, 4-8 GHz and 8-9 GHz. Considerations on the design. construction and testing of these devices are described. The achieve performance is state-of-the-art, with about 9.7 K/GHz noise temperature and about 13 dB of gain per stage at a cryogenic temperature of 12 K. The applications for these amplifiers are various, even though they are designed for the intermediate frequency (IF) part of superconducting-insulating-superconducting (SIS) heterodyne receivers; they are also currently being used as radio frequency (RF) front-ends for C-band and X-band receivers at Onsala Space Observatory 20 m and 25 m telescopes.