Wideband Absorptive Common-Mode Filter Based on Hybrid Structures of Quarter-Wavelength Slot and Microstrip Resonators

This paper presents a novel wideband absorptive common-mode filter which is constructed by differential microstrip lines, two hybrid resonator unit-cells made of quarter-wavelength slot and microstrip structures, two lumped resistors, and a ground plane. Two resonator structures, including quar-ter-wavelength slot and microstrip lines, share the same resonant frequency at which the common-mode energy can be absorbed by lumped resistors. Furthermore, two resonator unit-cells are cascaded symmetrically beneath differential lines to realize bidi-rectional and wideband common-mode absorption. The measured results show that the proposed common-mode filter can exhibit low insertion loss for differential signals, and achieve a wide absorptive stopband from 1.55 to 2.65 GHz (Absorption ratio > 90%) with 52.38% fractional bandwidth simultaneously.