Measurement and Calibration Approaches for Two-Port Scattering Parameters at mK Temperatures

This paper describes the developed set-up and the characterization approaches to realize full two-port, calibrated scattering parameters measurements at cryogenic temperatures, providing a complete uncertainty budget. The system developed at the Istituto Nazionale di Ricerca Metrologica (INRiM, Italy), exploits the Short-Open-Load-Reciprocal technique, to realize error corrected cryogenic measurements with single cooling cycle. The system operates at temperatures down to the mK range, in the band 4-12 GHz in coaxial line. Calibration standards are referred to traceable room temperature measurements, while a numerical approach is used to evaluate the artifact response shift from room temperature values, and derive key information to enable full measurement uncertainty budget. Moreover, relevant measurement uncertainty contributions are evaluated according to internationally agreed procedures, and a comprehensive uncertainty budget is presented. Test measurements on a 20 dB attenuator are shown as an example. An attenuation value of 20.70 +/- 0.08 dB (95% confidence interval) was obtained at 6 GHz.