A low-noise cryogenically-cooled 8-12 GHz HEMT amplifier for future space applications

A two-stage 8–12 GHz (X-band) cryogenically-cooled Low-Noise Amplifier (LNA) has been developed with a commercial pseudomorphic HEMT on AsGa substrate. In a first step, different commercial transistors have been fully characterized from 300 K to 20 K using a new method to measure the four noise parameters. Preliminary results have allowed the selection of the best device. This enabled the design of the two-stage LNA with the help of a microwave CAD software.In a second step, the LNA has been characterized at 300 K, 30 K and 4 K. As the physical temperature decreased from 300 K to 30 K, the LNA exhibited an average gain increase of 2 dB and as much as a fourfold reduction of noise temperature. A noise figure of 22.5 K and a gain of 23 dB have been achieved at 30 K around 10 GHz. The noise temperature has been furthermore reduced to 20 K by cooling the amplifier at the liquid helium temperature (4.2 K). Different methods to measure the noise characteristics of the amplifier are widely developed in this paper.