Noise properties of cryogenic microwave amplifiers and relevance to oscillator frequency stabilization

We studied noise properties of a new generation of energy-efficient microwave low-noise high-electron-mobility-transistor amplifiers. The noise measurements were conducted both at room and cryogenic temperature with the amplifiers strongly decoupled from the environment to reduce the influence of ambient temperature fluctuations on their phase noise spectra. Our results show the importance of keeping the amplifiers operating in the small-signal regime if they are to be used for applications such as precision electromagnetic measurements and oscillator frequency stabilization.