Study On Electromagnetic Radiation Emission Test Equipment Of Non-full Shielding For Electronically Large Size

High-speed EMU is a system with large size,complex internal power electronic equipment and complex cable and wire harness.In the process of the on-site radiated emission test,there is some influence on the accuracy of the results because of the background noise.In order to solve this problem,some researches have been done to suppress the background noise in radiated emission test,which includes virtual chamber measurement,time-domain EMI measurement and so on.Although these methods,to some extent,have been improved and background noise has been suppressed,there are still some problems in aspect of real time and the accuracy.To improve these problems,a non-full shielding radiated emission measurement method is proposed.This thesis aims at the related performance of the test device of non-full shielding.And the suppressing background noise and receiving radiated field as the main content were analyzed by theory,numerical simulation and experimental verification.First,the problems in the process of field testing were introduced and analyzed.Meanwhile,the non-full shielding radiated emission measurement method was researched,and the device was developed.Besides,the subsystems were illustrated.According to the shielding principle,the background noise suppression of the non-full shielding radiated emission test device was analyzed.Secondly,the non-full shielding radiated emission test device was modeled and simulated through the HFSS(High Frequency Structure Simulator)simulation software.The distribution characteristics of the radiated electromagnetic field and the background noise in non-full shielding cavity were analyzed.In addition,the influence of the measured radiation field and the background noise from different directions for the field distribution characteristics were analyzed.Furthermore,the field distribution of the measured radiated electromagnetic field and background noise with different frequencies at the receiving terminal of the antenna was discussed and summarized.Finally,based on the above theories and simulation analysis,the related experimental verification was set up.The results of the simulation showed good consistency with measurement result.The experimental results verified the field distribution characteristics of the radiated field in non-full shielding cavity by simulation and analysis.In addition,the field distribution of the radiated field and the background noise with different frequencies as well as directions at the receiving antenna terminal was proved respectively.The simulation and experimental results showed that the oblique polyurethane pyramid for absorption loss is better than the straight one.Besides,after loading the absorbing material in the shielding cavity,the standing wave component of the measured radiation field in the non-full shielding cavity was reduced,and the influence of the non-full shielding cavity for the accuracy was ensured to be within 3dB.The background noise can be attenuated by the non-full shielding cavity and the value can reach from 20 dB to 30 dB,and the more deep for the position in the cavity,the attenuation will be more obvious.When the incident angle of the measured radiated electromagnetic field and background noise changed 10°,the field strength at the antenna terminal can be decreased from 2dB to 3dB.Furthermore,the background noise can be attenuated by the absorbing material further,and the attenuation increased about 20 dB.In a word,the measurement method of non-full shielding radiated emission can not only accurately receive the measured radiated field,but also effectively suppress the background noise.