Uncertainties Caused by Noise for Microwave Interferometric and Reflection Measurements of Extreme Reflection Coefficients

This article concerns an uncertainty analysis of interferometric transmission measurements and standard reflection measurements of extreme impedances (extreme reflection coefficients) and broadens the scope of previously published works. Specifically, this article focuses on revealing fundamental limits influencing achievable measurement accuracy and precision by means of the law of uncertainty propagation (LUP). The analysis considers the sources of uncertainty influencing every measurement, in particular phase noise and thermal noise. The proportion of uncertainties of standard reflection measurements and interferometric measurements is derived theoretically and experimentally verified for two cases with dominant either the phase noise or the thermal noise. The values determined experimentally in a frequency band from 2 to 4.5 GHz agree well with the values derived theoretically.