Wideband balanced reflectionless filter with common-mode noise absorption

This paper presents a wideband balanced reflectionless filter based on the half-wavelength ring resonator. The proposed structure is simple and easy for manufacture. The design procedures are elaborately introduced. To promote understanding, the analysis of differential-mode (DM) and common-mode (CM) equivalent circuits are given. The corresponding equations are derived. For validation, a design example is fabricated and tested. The measured results verify its ability of transmitting DM signals and eliminating undesired CM signals. Specifically, the 21.6-dB CM suppression bandwidth can reach up to 273%, while the CM absorption bandwidth can reach up to 195%. The proposed balanced reflectionless filter exhibits excellent DM matching level, CM suppression level, and wide reflectionless bandwidth.