Research On Radiated Emission Modeling Of High Speed Circuits Based On Near-field Scanning

Along with the rising of the circuits’ clock frequency, PCB’s working frequency has entered into the microwave frequency band, where the size of PCB trace and on-board devices will reach or even greater than 1/4 wavelength, which means they shall become efficient radiators of electromagnetic energy due to the antenna effect. Hence, it is increasingly important to consider the electromagnetic interference (EMI) characteristic of PCB in its electromagnetic compatibility (EMC) design phase. Full-wave analysis method is often applied to the quantitative analysis of the EMC characteristic of PCB. However, as the growing complexity of the PCB circuits, huge computational burden will be brought. Furthermore, it is always the case that the details of PCB design are unknown in the design phase, thus, nothing can be done by full-wave analysis in such complicated condition. Given all this, this dissertation proposed a very flexible solution for substituting the PCB complex radiators by simple near-field scanning-based equivalent model, which does not require the detailed structure of PCB. Then, we can combine the obtained equivalent model with finite element method based full-wave analysis tool-HFSS to evaluate and analysis the EMI characteristics of PCB. Based on the analysis of the near-field scanning problems encountered in engineering measurement, some equivalent modeling methodologies are studied, and the following achievements have been obtained.1. An equivalent magnetic-dipole array model based on near-field magnetic amplitude and phase scanning is proposed. Regularization optimization method is adopted to solve the equivalent model, based on which the PCB’s EMI characteristic in both whole free space and in a shielding box are studied with assistance from a full-wave solver. By using this equivalent modeling method, the diffraction effect of PCB’s ground plane and the interaction between the PCB and the shielding box can be well considered.2. In view of the difficulty of tranditional phase-less near-field scanning-based equivalent dipole model in meeting the demands of modeling speed and modeling accurcay, an equivalent magnetic dipole model based on repeated particle swarm optimization (RPSO) algorithm is proposed to balance against the modeling speed and modeling accuracy. In this proposed method, the number of equivalent dipole and the position and moment of each dipole are determined by RPSO procedure.3. In order to further improve the modeling accuracy with "sufficient " dipole number and without much degradation of modeling speed, a hybrid RPSO and iterative source reconstruction (ISR) method is proposed to establish an equivalent magnetic dipole array model. With a robust initial phase of magnetic near-field provided by RPSO procedure, ISR method is adopted to solve the equivalent model by employing an iterative source reconstruction and source correction procedure.4. To meet the requirement of the rapid analysis of wide-band PCB EMI characteristic, a proposed wide-band equivalent hotspot magnetic dipole model is built based on a near-field magnetic hotspot scanning. With the help of PSO procedure, the wide-band equivalent hotspot magnetic dipole model is obtained, which makes the rapid prediction of the wide-band PCB maximum electric far-field strength possible.