In this paper, a new dipole-moment model based on near-field scanning for representing equivalent IC radiation emissions on a PCB (Print Circuit Board) is presented. One set of dipoles (both electric dipoles and magnetic dipoles) are used to characterize near-field and far-field radiation from the source. In order to build the model, tangential electric field and magnetic field on a Huygens's box enclosing the radiation source are needed. Both the phase and magnitude of these tangential fields are obtained either in simulation or in measurement by near-field scanning method. Two steps are established to reconstruct the dipole moment. Firstly, a set of dipole array is used to predict far-field radiation from the source with the least-square method. Then, another set of dipoles which make contributions to the near-field only are added in for accurate calculation of near-field. The dipoles used for predicting far-fields are further distributed into dipole arrays but the value summation of them is equal to each of the dipole used for the far-field matching. All types of dipoles used have the same number and are distributed on the area of the same size and positions. Finally, these two sets of dipole together are able to characterize both near-field and far-field radiation from the source simultaneously. Two examples are used to demonstrate the approach. A U-shape trace model is built in HFSS and the dipole-moment model is validated by simulation. In another example, IC radiation is modeled by dipole-moment and the method is verified by measurement data based on near-field scanning technique. This new dipole-moment model can predict both the near-field and far-field radiation well which is useful in analyzing radio-frequency interference issues.
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