A Broadband and High Absorption Efficiency Common-Mode Filter Using π-Type DGS With Z-Shaped Bridge and Interdigital Capacitor

In this article, an absorptive common-mode filter (A-CMF) with a broadband common-mode (CM) noise suppression and a high absorption efficiency is proposed. The designed A-CMF is constructed with two π-type defected ground structures, which are distributed by spatial multiplexing technology to reduce the circuit size. Three transmission zeros (TZs) are introduced to achieve a better CM noise mitigation characteristic. Z-shaped bridges and the interdigital capacitor are etched to adjust the locations of the TZs, which can enlarge the noise suppression level and bandwidth for improving the absorption efficiency. By loading the absorptive resistor on the input port, the reflected CM noise can be absorbed to minimize the influence on the adjacent circuits. An equivalent circuit model is built to explain the mechanism of the presented A-CMF. In order to validate the proposed concept, a circuit sample is fabricated and measured with an absorption efficiency of more than 95% from 5.2 to 9.8 GHz. Moreover, a CM noise suppression bandwidth of 58% is observed with a rejection level of better than 20 dB. Good agreement can be observed between the measured and simulation results.