Design Of Anti-electromagnetic Interference Circuit For The Receiving Module Behind Airborne VHF Antenna

With the improvement of the complexity of the aeroelectromagnetic environment and the sensitivity of airborne electronic equipment,the very high frequency(VHF)communication system used in the near-range information transmission of civil aircraft is more vulnerable to electromagnetic interference.As an importment part of communication system and the weak electromagnetic link,the receiving module behind VHF antenna has a direct impact on the communication safety of aircraft.At present,most of the electromagnetic protection modules of aviation VHF communication equipment developed at home and abroad are low-frequency lightning protection modules,which have poor ability to suppress the in band electromagnetic interference signals emitted by radar and radio station.This paper focuses on the back-end receiving module of airborne VHF antenna,and by studying its electromagnetic sensitivity,the band-pass filter for frequency domain protection and PIN limiter for energy domain protection are designed to improve the electromagnetic protection ability of the receiving module.Firstly,based on the electromagnetic coupling theory,the main coupling path analysis of airborne VHF communication equipment,the interference threshold research of low noise amplifier(LNA)and the comparative analysis of front-door coupling protection measures are carried out,in order to determine the main design method and basic index requirements of the anti electromagnetic interference circuit.Secondly,the influence factors of the output response of the filter are studied by simulation,as well as a butterworth band-filter with high filtering performance is designed by combining parameter calculation and optimization.Thirdly,based on the harmonic balance method,the influence of PIN diode parameters on the insertion loss and limiting level of the limiter is analyzed.In addition,the influence of PIN series,phase shifting network and DC bias voltage on the performance of the limiter is simulated,and a low insertion loss active limiter is designed,which improves the limiting performance of the limiter.In order to reduce the power consumption and improve the stability of the active limiter,the directional coupler and rectifier circuit are used to replace the bias power supply to rectify part of the electromagnetic interference signal into DC.Finally,the S-parameter and high-power continuous wave injection test schemes are proposed for the two kinds of electromagnetic protection modules.The passband and stopband attenuation values of the filter and the insertion loss,limiting level and power capacity of the limiter are tested.The measurement results show that the protection module can effectively improve the anti electromagnetic interference ability of airborne VHF receiver module.