For the possible application to the cryogenically cooled low noise HEMT amplifier, this paper presents scattering parameter measurements of a HEMT chip at room and liquid nitrogen temperatures and in the 1-20 GHz frequency range. The measurement method which uses the well known TRL calibration technique will be fully discussed. S parameters and noise parameters measured at room temperature by means of this technique have been used to design a single stage low noise amplifier for the K band. Without any tuning this amplifier has an overall noise figure value of 1.6 dB with a 7 dB associated gain at 18 GHz which is in good agreements with predictions
