Cryogenically Cooled Broad-Band Gaas Field-Effect Transistor Preamplifier

A cryogenically cooled 1-2 GHz low-noise broad-band prototype preamplifier utilizing GaAs field-effect transistors is described. The preamplifier has an average gain of 30 dB and 35 dB at ambient temperatures of 293°K and 18°K, respectively. The noise figure has a minimum value of 0.75dB at 300°K and 0.24dB at 18°K. The optimum preamplifier operating conditions for a minimum noise figure at temperatures of 293°K, 80°K and 18°K are given and are discussed. Also, the phase-shift characteristics, the input and output voltage standing-wave ratio as a function of frequency and intermodulation products content as a function of the input power level were measured.