OPTIMIZATION OF INPUT IMPEDANCE AND MECHANISM OF NOISE SUPPRESSION INA DC SQUID RF AMPLIFIER

The optimal input impedance and noise of a de SQUID RF amplifier at fr equencies of the order of 1 GHz with a resonant input matching circuit has been studied analytically, numerically, and experimentally, A mod el for noise temperature and power gain has been developed for the pra ctical resonant input tank circuit, A new effect of the output noise i ncreasing or decreasing with changing the sign of voltage-to-flux tran sfer coefficient has been observed experimentally and explained analyt ically, The different values of noise temperature for the opposite dV/ d Phi values have been interpreted using a model with partially correl ated current and voltage noise sources, The equivalent layout for opti mal input matching of a SQUID amplifier comprising series and parallel resonant circuits has been presented, Using such matching circuit and SIS junction as a signal source the SQUID amplifier noise temperature about 1 K has been measured at 1.1 GHz.