Research On The Notch Filter For EMC Measurement Of Railway Wireless Communication Equipment

Railway wireless communication equipment is usually installed in a small space,and the problem of electromagnetic interference between the apparatus becomes particularly prominent.In order to ensure these apparatus is working properly in on-site application,it is very important to test the electromagnetic compatibility of these apparatus.For railway wireless communication equipment,the communication signal is much larger than the electromagnetic disturbance signal in electromagnetic emission(EMI)measurement,it will lead to overload of the measurement receiver or a non-linear spurious response.Based on the comparison between the EMI measurement standards of railway apparatus and other industry-related measurement standards,this thesis researched and designed three special band-stop filters for EMI measurement,which improves the accuracy of the EMI measurement results for railway wireless communication equipment.First of all,this thesis introduced the measurement site,devices and layout for electromagnetic emission measurement based on the standards of railway electronics and electrical equipment,analyzed the principle of nonlinear distortion produced by the test receiver in the EMI measurement of railway wireless communication equipment,A band-stop filter was used in the measurement system to solve the problems above.Then,this thesis analyzed the design principles and methods of the band-stop filter,and designed and simulated three special notches(narrow-band band-stop filters)for measurement.For the radiated emission measurement of in-vehicle BTM equipment,A LC band-stop filter was used to suppress the excessive transmit power at its 27.095 MHz communication frequency.A third-order Chebyshev LC band-stop filter was designed and simulated,and its stop-band bandwidth is 0.01 MHz,stop band suppression was-40 d B,and the-3d B bandwidth was 6MHz;Aiming at the band-stop filter required for the measurement of radiated emissions of 450 MHz locomotive radio stations,this thesis also designed a very narrow-band tunable cavity band-stop filter using weak coupling method,which was different from the traditional cavity band-stop filter.The weak coupling method with the side of the resonant cavity can make the stop band of the band-stop filter extremely narrow,and the resonator adopts the SIR(step impedance)cavity structure to facilitate the miniaturization of the cavity.The relative bandwidth of the filter was only 0.2%,the suppression depth reaches-35 d B,and the center frequency and stop band bandwidth can be adjusted to meet the measurement requirements;A special band-stop filter was designed for radiated emission measurement of GSM-R communication equipment,this thesis also used the SIR and weakly coupled cavity structure,while increasing the loading capacitance of the resonant cavity to expanded the spurious stop band to 7 times of the center frequency,the horizontal distance of the band stop filter was reduced by folding the main transmission line.The band-stop filter had a bandwidth of 4MHz and a suppression depth of-30 d B,which fully met the test requirements.At the same time,this thesis also simulated and analyzed the influence of each structural size of the cavity on its performance.Finally,this thesis analyzed the sensitivity of the main design parameters of the two band stop filters to their performance,in order to predict the influence of component and size errors on the performance of the band-stop filter.,Based on the simulation,the two band-stop filters were made and their S parameters were measured.The measurement results showed that these two band-stop filters met the needs of the electromagnetic emission measurement for railway wireless equipment.