Cryogenic noise parameter measurements of microwave devices

A robust measurement technique, the seven-state method, which is well suited to noise parameter measurements at cryogenic temperatures is presented. In contrast to existing concepts, the seven-state method makes it possible to determine the minimum noise figure F/sub min/ and the equivalent noise resistance R/sub n/ except for a constant term m with the help of noise power measurements with a noise source operated at ambient temperature only. The optimum generator admittance Y/sub opt/ and the input admittance Y/sub in/ of the device under test are completely calculable from cold noise power measurements. An additional measurement of Y/sub in/ with a network analyser as needed for other techniques is not necessary. In order to determine the unknown factor m, one further noise power measurement with a hot noise source has to be performed. A measurement system as well as measurements which were performed on AlGaAs/InGaAs HEMT transistors at ambient and cryogenic temperatures are presented.