Design of a cryogenic amplifier with a cascaded network

A cascaded 2-port network matrix method was used to optimize the voltage standing wave ratio (VSWR) and the noise in a cryogenic RF amplifier. The S matrix transform of the transistor circuits was used to derive analytic expressions for the gain, VSWR and noise of the preamplifier. The transistor source inductive feedback was analysed to optimize the noise matching. A semi-lumped, cryogenic amplifier for a code division multiple access (CDMA) system fabricated and measured at 77 K with VSWRi as 1.3, VSWRo as 1.7, gain greater than 18 dB, noise temperature below 30 K show the accuracy of the design method and the noise model.