A method for modeling electromagnetic emissions from printed circuits with equivalent dipole sources is presented. An optimization procedure based on the genetic algorithm is used to determine the number of equivalent dipoles and their parameters by fitting to the measured near fields. Prediction of emissions from the PCB can then be obtained by computing from the equivalent model without reference to the details of the PCB.
I. INTRODUCTIONThe effects of electromagnetic emissions from printed circuit boards (PCBs) with fast clock are becoming an important topic in the design of electronic devices. The issues of electromagnetic compatibility (EMC) of PCBs include not only predicting the far fields, but also identifying the primary radiating sources. Therefore, the idea of representing a PCB with a set of equivalent currents or dipoles is attractive because of its simplicity. An infinitesimal dipole is the simplest radiator which can be plugged and played in any electromagnetic package, thus modeling with equivalent dipole sources dramatically reduces the complexity of modeling emissions from a complete PCB.For most approaches, the equivalent source is deduced from the measured near-field distribution as near-field measurement has advantages in high accuracy and reliability. In [1, 2], an antenna is represented by equivalent magnetic or electric currents over a fictitious plane, and the sources are determined from both magnitude and phase information of near-field data by an electric field integral equation. The use of equivalent magnetic currents was extended to the level of printed antennas in [3]. It is also reported that the far field is determined from only the near-field amplitude over two surfaces with a phase retrieval algorithm [4]. Finally, in our previous work [5], an equivalent dipole model is discussed which replaces a PCB with an array of equivalent magnetic dipoles placed in a pre-fixed grid on a 2D surface. The dipoles are determined by directly fitting the scanned near-field data.In this paper, an alternative method is presented for equivalent source identification of PCBs. The PCB is represented by an array of magnetic dipoles found from an optimization procedure using the genetic algorithms based on near-field scans. Radiations from the PCB can then be obtained directly from the equivalent dipole model. The proposed model retains the advantages of computational simplicity and accuracy. Furthermore, the number of dipoles
A method for characterising and modelling the noisy electromagnetic fields from complex circuit boards using a simplified representation of correlated dipoles is investigated. It is shown how the equivalent dipole model can be constructed from the time domain measurements of the near fields. This equivalent model can then be used to accurately reproduce the emissions from the circuit board in both the near and far field. However, it is found that there are many challenges to such an approach as such a technique will require a large measurement data set to be acquired which may be very time consuming and the solution can be ill conditioned.
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