High-performance, 2.5-K cryostat incorporating a 100–120-GHz dual polarization receiver

A hybrid cryostat is described which was designed to cool two SIS mixers in a 100–120-GHz dual polarization receiver. A mechanical refrigerator is used to cool radiation shields surrounding a 4.3-l capacity metal tank containing liquid helium (He4). The temperature of the liquid can be lowered to 2.5 K by reducing the helium vapor pressure in the tank with the aid of a mechanical vacuum pump. A liquid hold time, at 2.5 K, of longer than five days has been achieved. With the mixers cooled to 2.5 K and L-band GaAs FET IF amplifiers cooled to 20 K, single sideband receiver temperatures of less than 120 K have been measured, with >15-dB image rejection and a useful instantaneous bandwidth of 500 MHz.