CRYOGENIC LOW NOISE AMPLIFIER

A radiofrequency amplifier includes a low noise amplifier (25) maintained in a hermetic cryostat structure (11) cooled by a cold head (30) and in which is maintained a low grade vacuum. The low noise amplifier receives signals from an input coupler (23) and transmits the signals through an output coupler (26). The input and output couplers are made, for a structural part, of a material with thermal conductivity equal or less than 50 W/m·K, and, for an electrically conductive part, of plating on at least one of the faces of the structural part, with a material with electrical conductivity more than 10E7 Siemens/m. The cold head includes at least two stages whose cold terminations are at different cryogenic temperatures, a base stage operating at a temperature close to the temperature at which the low noise amplifier must operate and at least one intermediate stage operating at an intermediate temperature.