The Loading Effect of Radio-Frequency Current Probes

The loading effect of radio-frequency current probes is here analyzed. A physical model, consisting of a lumped impedance in series with the flow of the current under measurement, is obtained. The correlation between the loading (insertion) impedance and the geometrical and physical characteristics of the probe is clearly described through formulas useful for design purposes. The model is compared with those existing in the technical literature and the main differences are highlighted and discussed. The theoretical predictions are experimentally confirmed. A direct application of the concepts here discussed to the improvement of the accuracy of the V/I type vector impedance measurements is also shown.