A cryogenically cooled two-channel paramp radiometer for 47 GHz

A new cryogenically cooled mm-wave parametric amplifier system for the 47 GHz region, the first field operational prototype, is described; the system comprises a 47 GHz radiometer using 18 K cooled degenerate parametric amplifiers, with parallel channels for two ortholinear or circular polarizations. The system features 300 MHz instantaneous RF bandwidth and up to 2 GHz tuning range; 100 K double-sideband system noise temperature at midband, and 0.16 K minimum rms noise fluctuation. Attention is given to the cooled circulator, varactor frequency doubler, the receiver cooling system, and system noise performance. Performance data indicate that future 100 GHz parametric amplifier systems for radiometry, communications, and radar may achieve single-sideband noise temperatures below 250 K when cooled to 20 K, or 700 K when uncooled, with at least 1.5 GHz bandwidth.