How to avoid resonance in multi-stage filtering of power FTU?

Multi-stage resonant filters amplify interference at specific frequencies, requiring parameter mismatch and damping suppression. In this design, the first-stage filter cutoff frequency is set to 10kHz (CMZ7060A-701T+4.7μF), the second stage to 30kHz (CMZ3225A-501T+1μF), and the third stage to 100kHz (PBZ2012E600Z0T+100nF). Small series resistors (10Ω/0.5W) are used between each stage to provide damping. SPICE simulation is used to verify the transfer function, ensuring the resonant peak is below -20dB. Actual testing uses a network analyzer to measure the S21 parameters of the filter network. This design achieves a gain of less than -30dB at the resonant frequency, and the filter network exhibits stable attenuation in the 10kHz-100MHz frequency band, meeting the IEC 61000-4-6 conducted immunity test requirements.