A Combined Method-of-Moments and Near-Field Measurements for EMI Evaluation of Switched-Mode Power Supplies

We propose an efficient modeling technique for the evaluation of radiated electromagnetic interference due to a switch-mode power supply mounted on a typical electronic printed circuit board (PCB). In the proposed model, first, the measured magnetic field on a rectangular plane in the vicinity of the PCB is used to identify equivalent current sources on the board surface by the method-of-moments. Having determined the radiating sources, the governing integral equations in free space are then utilized to compute the magnetic-field distribution at a desired distance from the PCB. The main feature of the proposed model is the use of both the magnitude and phase of the near-magnetic field for identifying the unknown current sources. This is found to be advantageous over the conventional models where the measurements are done on two separate planes or involve time-consuming heuristic optimization algorithms to invert the measured magnetic-field data into unknown current sources. The validity of the proposed technique is demonstrated by comparing the actual and reconstructed field radiations due to several simulated and fabricated sources.