Field Coupling Mechanism Investigation of mm-Wave Magnetic Near-Field Probe Based on a Generalized Equivalent Circuit

A field-response-equivalent circuit is advantageous for explaining the field coupling mechanism of H-field probes. Previous works have primarily explained the coupling between a field probe and the calibration kit. In this article, a field coupling circuit model is proposed in a generalized form to directly predict the voltage induced by the H-field and the unwanted E-field in the probe for the millimeter-wave (mm-wave) range. The field response circuit model is based on the loop impedance model and incident field response of a loop antenna in the form of a series expansion. This article reveals that the zero-mode response corresponds to H-field coupling, whereas the first mode corresponds to E-field coupling and is validated through the numerical simulation based on the circular loop antenna. The coupling of the fabricated H-field probe is predicted based on the equivalent circuit model and the prediction matches numerical simulation and measurement results from 1 to 40 GHz. The equivalent circuit can be used to predict the probe field coupling with an error less than 4 dB. Finally, this article provides a generalized equivalent circuit as a tool to analyze and understand the probe field coupling quantitively. This article reuses some content from a thesis (Liu, 2021) in Sections I-III with permission.