Quantifying the Impact of RF Probing Variability on TRL Calibration for LTCC Substrates

When conducting radio frequency (RF) measurements using microwave probes, slight misplacements of the probing tips introduce errors and deteriorate measurement results, especially in the case of manual probing. For this reason, short transmission lines in combination with polynomial chaos expansion (PCE) are used to model the imperfect connections between probes and launching structures, and to quantify the impact of probing inaccuracies on the thru-reflect-line (TRL) calibration technique. The analysis is accompanied by a comparison between PCE and Monte Carlo sampling (MCS) in order to assess the accuracy of the proposed method. Additionally, a set of microstrip TRL standards are manufactured on a low temperature cofired ceramic (LTCC) substrate and subsequently measured in the frequency range from 0.05 to 50 GHz for the purpose of studying the correlation with the underlying PCE model.