Measurement of Near-Field Electromagnetic Emissions and Characterization Based on Equivalent Dipole Model in Time-Domain

In this article, a method for representing electromagnetic emissions from a device under test (DUT) using an equivalent time dependent dipole array model deduced from the time-domain near-field scanned tangential magnetic fields is proposed. First, a three-dimensional (3-D) time-domain near-field scanning system is established to measure the tangential magnetic fields emitted from DUTs which are a transmission line above a ground plane and a printed circuit board (PCB) with several microstrips, respectively. For time-domain measurements, two magnetic field probes are calibrated over a broad bandwidth for both amplitude and phase to obtain their complex probe factors. Then, the measured magnetic fields are utilized to construct an equivalent time dependent dipole array model to represent the electromagnetic sources of the DUT. Parameters of the time dependent equivalent dipoles are directly calculated by fitting to the measured magnetic fields. The effects of different number of dipoles on the accuracy of the reconstructed magnetic fields from the PCB are studied. The reconstructed equivalent dipoles of the DUTs can be used to predict the electromagnetic fields at other observation levels. The results predicted by the equivalent dipole model are in agreement with the simulated and measured results.