Radiofrequency amplifier for low power radiofrequency signal reception device including a low noise amplifier maintained in a hermetically sealed space delimited by an envelope of a cryostat in which space a reduced interior pressure is maintained compared to the external atmospheric pressure, said low noise amplifier receiving signals to be amplified from an input coupler crossing the envelope in a sealed manner, and transmitting the amplified signal through an output coupler crossing the envelope in a sealed manner, said space being cooled by a heat pumping cold head inside the structure characterised in that in the radiofrequency amplifier: - The input and output couplers are made, for a structural part, from a material with thermal conductivity equal or less than to 50W/m.K, and for an electrically conductive part by a plating on said structural part made of a material with electrically conductivity higher than 10E7 Siemens/m. - The internal pressure in the envelope of the cryostat, before its temperature is reduced, corresponds to a low grade or primary vacuum pressure of between atmospheric pressure and 10Pa. - The hermetic space delimited by the envelope is filled with a silicon based nano-structured thermal insulation in the form of an aerogel. - The cold head includes at least two stages (302, 303) whose cold terminations (304, 305) 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 a temperature between that of the base stage and ambient temperature, a cold termination (305 of the base stage being thermally linked (315, 316) to the low noise amplifier in order to implement heat pumping of said low noise amplifier and an intermediate cold termination of the at least one intermediate stage being thermally linked to support structures or to internal elements of the amplifiers in order to achieve distributed heat pumping inside the envelope. - The input and output couplers are made, for a structural part, from a material with thermal conductivity equal or less than to 50W/m.K, and for an electrically conductive part by a plating on said structural part made of a material with electrically conductivity higher than 10E7 Siemens/m. - The internal pressure in the envelope of the cryostat, before its temperature is reduced, corresponds to a low grade or primary vacuum pressure of between atmospheric pressure and 10Pa. - The hermetic space delimited by the envelope is filled with a silicon based nano-structured thermal insulation in the form of an aerogel. - The cold head includes at least two stages (302, 303) whose cold terminations (304, 305) 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 a temperature between that of the base stage and ambient temperature, a cold termination (305 of the base stage being thermally linked (315, 316) to the low noise amplifier in order to implement heat pumping of said low noise amplifier and an intermediate cold termination of the at least one intermediate stage being thermally linked to support structures or to internal elements of the amplifiers in order to achieve distributed heat pumping inside the envelope.