Low noise microwave parametric amplifier

A low-noise temperature microwave amplifier is described. This amplifier is a nearly degenerate superconducting parametric amplifier at X-band consisting of a low-beta, thin-film, single-junction SQUID, a monolithic 50-ohm to 1-ohm impedance matching network, and a cooled circulator. Nb/Nb2O5/Pb alloy junctions were incorporated into Nb and Pb-1n circuitry on 1 x 2 cm silicon chips. The SQUID was phase-biased near 90 deg and driven by an external pump at approximately twice the operating frequency. The self-resonance frequency of the SQUID inductance and junction capacitance was set at the operating frequency of 8.2 GHz. The operating characteristics depended on the pump amplitude, the junction phase bias, and the SQUID parameters. For small values of beta less than 1, the maximum gain in both the signal and idler channels was about 10 dB, the bandwidth about 170 MHz, and the single-sideband noise temperature was 6 K with an uncertainty of (+ 15 to - 7) K. For higher beta, the gain increased to nearly 30 dB with increased noise and parametric oscillations occurring near the pump subharmonic frequency.