Abstract
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.
Highlights
MODERN digital systems incorporating some complex active integrated circuits and passive lumped components work within a variety of environments
In order to validate the accuracy of the experimental procedure and the proposed method, an observation point, which is at the middle of transmission line (TL) (x=142.5 mm, y=142.5 mm) and 5 mm above the TL, is selected to compare the measured and estimated tangential magnetic fields (magnetic fields in x-direction denoted as ܪ௫()ݐ, magnetic fields in y-direction denoted as ܪ௬()ݐ, at the center of the probe) over the time range in Fig. 8 and good agreements are obtained
The results demonstrate the effectiveness of predicting the propagation away from the reference plane where the source dipoles are deduced (5 mm above the TL) as from Table I the 10 mm height has similar errors
Summary
MODERN digital systems incorporating some complex active integrated circuits and passive lumped components work within a variety of environments. Measurements and analyses of the near-fields in the time-domain are becoming increasingly important for characterizing the electromagnetic emission properties of the DUT. This is because it is recognized that the interference in many digital systems and communications links are better quantified in the time-domain [13] and time-domain analysis can be more efficient [14]. The proposed approach in this paper is based on equivalent time dependent electric dipole array model which is inherently broadband and can provide information on the time dependent properties of the magnetic fields from the DUT.
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