Circuit Modeling And Analysis In EMI Near-field Scanning System

With the increasing integration and operating rate of circuit systems,electromagnetic interference(EMI)will occur on chips and modules,which has serious influence on the electromagnetic compatibility of circuit systems.It is important to obtain the electromagnetic radiation information from the radiation source and accurately locate the radiation source in the way of near-field scanning.Near-field scanning is very useful for studying the electromagnetic interference problem.A near-field scanning system mainly includes probes,cables,amplifiers,and measuring instruments.Calculating the system factor of a near-field scanning system is the key to convert measured voltage into measured field strength.The system factor of a near-field scanning system is defined as the ratio of the simulated field strength to the measured voltage at the probe position at different frequency points.The measurement voltage beyond the linear dynamic range of the near-field scanning system will cause distortion of the system factor,which will affect the accuracy of electromagnetic detection.Therefore,modeling and analysis of the circuit in EMI near-field scanning system and determining its linear dynamic range are main technologies for EMI measurement.The main work of the thesis includes two aspects:I.The circuit modeling of EMI near-field scanning system is studied,including probes,cables,amplifiers,and measurement receivers.And the influence of the noise figure,gain and 1d B compression point on the sensitivity and linearity of a near-field scanning system is analyzed.The formula for calculating the linear dynamic range of a near-field scanning system is also derived.The modeling and analysis of a near-field scanning system provide theoretical guidance for the design and construction of a near-field scanning system.In addition,the near-field scanning system is set up with a loop magnetic probe,high-frequency cables,broadband amplifiers and a spectrum analyzer to realize high-performance near-field electromagnetic detection.?.The method of calculating the system factor in EMI near-field scanning system is studied.Firstly,based on the measurement and simulation of the standard microstrip line,the system factor is calculated within the linear dynamic range of the near-field scanning system at different frequencies.And the operating frequency range of the near-field measurement system is analyzed.Secondly,an ordinary microstrip line is used as a device under test,and the simulation and measurement results of the near magnetic field are analyzed to verify the accuracy of the formula for calculating the system factor.Finally,the near-field scanning system is used to measure the horizontal magnetic field strength above the FPGA board,and two-dimensional magnetic field distribution is mapped.