点火电路中低通滤波器的接地对其性能的影响

火箭发动机的点火电路中常串联低通滤波器来消除高频干扰信号。在理想情况下，低通滤波器的插入损耗会随干扰信号频率的增大而增大，但在实际使用中，低通滤波器的接地回路中会有接地阻抗，导致干扰信号频率无限增大时，低通滤波器的插入损耗会减小；并且通过实际测试，接地阻抗越大，插入损耗会越小。为此在点火电路中应减小低通滤波器的接地阻抗，来有效防止高频干扰信号使发动机误点火。

Earthing effect on performance of the lowpass filter in ignition circuit

In order to eliminate high frequency interference in the ignition circuit of Rocket Motors, the lowpass filter is usually cascaded. Ideally, the insert loss of lowpass filter increases along with frequency of interference increase, but in practical application process, there is earthing resistance in the earth return of lowpass filter, it lead to decrease of insert loss with the increase of frequency infinitely, the more of earthing resistance the less of insert loss. So the earthing resistance of lowpass filter should be decrease in the ignition circuit, in order that it can effectively prevent igniter from being ignited wrongly by the high frequency interference.