Design of Absorptive Common-Mode Filters Based on Coupled Stripline λ/4 Resonator

This article presents an absorptive common-mode filter (A-CMF) design method based on coupled lambda/4 resonator. The equivalent circuit model (ECM) is established and discussed to investigate the working mechanism. Here, a stripline is adopted to verify the design method due to its strong immunity to interference and low radiation loss. To realize wideband CM noise suppression, a second reflective CMF (R-CMF) is developed first. Then, the concept of asymmetrical bidirectional A-CMF is proposed, and two types of A-CMFs for single-frequency and wideband absorptions are developed and evaluated. A prototype of the proposed A-CMF is fabricated and tested, and the experimental results demonstrate that the proposed A-CMF could achieve a 90% absorption band from 4.75 to 6.03 GHz, while the DM signal could pass through from dc to 8 GHz. The proposed design method only needs to insert the resonator in the middle of the differential lines and would not occupy extra area, thereby providing a promising way for system design.