Accuracy Assessment of Non-Intrusive Measurement of Two-Port Impedance and Admittance Parameters by Inductive Couplers

Many applications, ranging from power electronics to electromagnetic interference modelling, take advantage of in-circuit impedance and admittance measurements, that is, carried out while equipment is operating. Single-port literature methods, based on the use of clamp-on inductive probes to couple the ports of a vector network analyser (VNA) with the system under test, are advantageous due to their non-intrusive setup, but are not suitable for multiport systems. Just recently, two-port inductively-coupled methods were proposed in two different formulations, namely, for measurement of the full 2x2 admittance and impedance matrix, respectively. In this paper, a comparative investigation on the accuracy provided by the inductively-coupled admittance and impedance measurement methods is presented. Both methods are tested using a suitable set of passive networks in the 150 kHz - 30 MHz frequency range. The obtained results are compared versus an accurate (yet intrusive) reference result, that is, impedance and admittance parameters mathematically converted from scattering parameters directly measured at VNA ports without using inductive couplers. The accuracy of both methods is quantified and discussed, providing useful insights on how to possibly improve the measurement setup.