EMI Near Field Measurement And Data Analysis

Communication equipment in the airport terminal area is gradually increasing,the degree of integration and miniaturization of the equipment is getting higher and higher.There are more applications of high-frequency and high-power equipment,which make the electromagnetic environment of the airport terminal area more complicated.The electromagnetic interference of communication equipment is also more complicated,and it is very important to diagnose the interference exceeding the standard and judge the source of the interference.The most important thing for the study of interference is to accurately locate the source of interference so that further anti-interference measures can be taken.At this stage,the near-field measurement of radiated EMI has become one of the important methods for electromagnetic compatibility pre-testing and fault diagnosis of equipment.The basic principles of electromagnetic radiation are introduced,and the near-field and far-field of electromagnetic radiation are explained,which lays a solid foundation for the study of subsequent near-field measurements.The principle of near-field measurement of the ring probe is mainly deduced,and the intensity of radiated electromagnetic interference is related to the induced voltage,which provides an effective idea for the diagnosis of EMI exceeding standard.Then in order to improve the measurement efficiency,measurement accuracy and measurement scale of radiated EMI,an improved electric ringlet probe is designed and used to construct an electric ringlet probe array for EMI near-field measurement.By changing different height,distance and power parameters,an open near-field test environment of same-frequency interference and in-band interference of dual signals is constructed.According to the actual measurement data,the radiation distribution of E-plane and H-plane of the tested omnidirectional antenna and directional antenna is visually displayed,and the spatial distribution state of the radiated signal is reconstructed.The radiated interference states under different interference distance,different interference power,same-frequency interference and in-band interference are given.It can be seen that the application of the probe array can not only improve the measurement efficiency and accuracy,but also reconstruct the spatial distribution of EMI,which is convenient for the analysis of the radiation distribution state.Finally,in order to more accurately determine the equipment’s over-standard EMI diagnosis and interference source,a dual signal source was constructed to analyze the interference magnetic field superposition form of the same frequency interference and different frequency interference,and the combined near-field probe array method was used to test the S mode signal in an open environment.The near-field EMI state parameters under the conditions of different interference frequencies,interference strengths and interference locations,analyze and summarize the combined characteristics of near-field electromagnetic interference fields.Three signal sources are constructed and two of the signal sources are used as interference sources to analyze the distribution of near-field EMI under multi-signal interference conditions.The study found that the useful signal near field is "sprayed" under the same frequency and different sites interference,the stronger the interference,the stronger the "jet",but there is an extreme value.The useful signal near field is enhanced and the shape is distorted under different-frequency and co-site interference with larger frequency difference.The stronger the interference,the more serious the distortion.The near-field state of the in-band inter-frequency interference is symmetrically distributed,the stronger the interference signal,the greater the near-field superposition between the useful signal and the interference signal,and there is an extreme value.Regardless of the single-interference condition or the multi-interference condition,the near-field EMI distribution follows the same change principle,and the same frequency interference has a greater impact on the signal than in-band interference.According to the characteristics of the interference near-field combination,a general procedure of interference diagnosis is proposed,which provides an effective method for the accurate judgment of interference sources in a complex electromagnetic environment.