Noise parameter measurement of microwave transistors at cryogenic temperature

A major drawback of active two-port microwave noise parameter measurement, by means of the multiple impedance technique at cryogenic temperature, lies in that a nonnegligible part of a lossy transmission line featuring a nonuniform temperature must be inserted between the automatic tuner (operated at room temperature) and the device input. Since the temperature distribution over that line is not precisely known, the contributed noise cannot be directly corrected. To overcome this, the use of a noise de-embedding technique is proposed, based on the measurement of a suitable noise standard made of a cooled mismatched two-port. By way of example, noise parameters of a GaAlAs/GaAs HEMT measured between 14 and 18 GHz at 77 K are reported. Finally, the accuracy of this technique is discussed