| The development and application of miniaturized high-speed integrated circuits(ICs)incur more electromagnetic interference(EMI)and electromagnetic compatibility(EMC)problems than ever before.A printed circuit board(PCB)is often composed of memory chips,radio frequency components,sensors,processors,antennas and other ICs.In order to make such a complex system work properly,it is crucial for engineers to rigorously analyze the potential EMI problems and work out feasible design schemes.However,it is quite challenging to characterize the complicated radiation sources by employing commercial full-wave simulation software,which is at the cost of computing time and memory resources.Worse yet,engineers sometimes even do not have the fullwave model of the device under test(DUT)due to commercial confidentiality.To tackle the issue,near-field scanning technique has been developed by measuring the near-field radiation pattern,and then reconstructing the equivalent sources to represent the real unknown sources.This dissertation mainly focuses on the difficulties of source reconstruction method in the real engineering,some innovative results have been achieved as shown below:Firstly,aiming at the accuracy and efficiency problem of the traditional source reconstruction method at single frequency,we proposed an effective source reconstruction method based on the phaseless near-field scanning by incorporating dynamic differential evolution(DDE)algorithm in this dissertation.The major difference between the proposed DDE and the conventional differential evolution(DE)is in the mutation and selection processes.The crossover process is the same for both conventional DE and DDE.Conventional DE updates all populations while the proposed DDE only updates every dipole in one population in each iteration.Therefore,the major advantages of the proposed method include that it converges faster and consumes less computing time,in comparison with the conventional DE method.The reconstructed equivalent dipole model can predict the near-field coupling and 3-meter far-field effectively and accurately.Both numerical and measurement studies have validated that the proposed DDE-based source reconstruction method is promising for EMI diagnosis.Secondly,aiming at the bandwidth problem of source reconstruction method in actual engineering,the approach we take is to fix the location of the dipoles and then just optimize the dipole moment by employing DDE algorithm.In this case,the equivalent dipoles with same positions can reuse the mesh in full-wave simulation,which is the basis of broadband modeling.Therefore,it can meet the need of broadband point modeling by using dipoles with different dipole moments at the same location to present EMI source at different frequencies.We also have proposed a broadband modeling method by using magnetic dipoles based on phaseless near-field scanning with the help of the DDE algorithm and interpolation method.The major advantage of this method is that the equivalent dipole model is constructed through fixing dipole locations by one-time simulation running.Then the equivalent dipole models of the whole frequency band are obtained by dipole moment interpolation.These equivalent dipole models can be used to represent the real EMI source in a broadband.Thirdly,aiming at the problem that the EMI sources can not be reconstructed accurately in the shielding enclosures,we propose an effective source reconstruction method for modeling unknown EMI sources in shielding enclosures based on phaseless near-field scanning.Firstly,an effective equivalent dipole model of an unknown source in free-space is derived by using the DDE method.Thereafter,a reconstructed matrix calculated by full-wave simulator is employed to build the relationship between the dipoles in the shielding enclosure and its near-field on the leakage plane,where the dipole positions are determined and fixed in the previous step.The dipole moments will be adjusted and optimized by again using DDE method based on the reference and reconstructed leakage fields.Both numerical and physical examples have been studied and the results have manifested that,the proposed source reconstruction method can effectively demonstrate the near-field behavior and accurately predict the noise coupling inside a shielding enclosure. |
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