VNA Tools II: S-parameter uncertainty calculation

This paper describes a software, METAS VNA Tools II, which is designed to compute uncertainties of coaxial S-parameter measurements. A bottom-up concept is used. Thus basic influence quantities are propagated through the calibration of the vector network analyzer to the S-parameters of a device under test. METAS UncLib is used for the linear propagation of uncertainties. The result is not only an uncertainty region but a list of uncertainty contributions with correlations. Thus the uncertainties can be propagated into eventual post-processing steps. In the present paper the concept has been verified by computing uncertainties of a calibration with a traditional quick short open load thru algorithm and an algorithm which involves optimization. The observed differences between the resulting uncertainties are lower than 0.3 percent, which can be explained by numerical inaccuracies.