A Novel Absorptive Common-Mode Filter for Cable Radiation Reduction

Abstract

An absorptive common-mode filter (A-CMF) embedded in a four-layer printed circuit board is proposed. Unlike traditional CMFs, for the A-CMF, common-mode (CM) noise is absorbed through the surface mount resistor, so the transmitted and reflected CM noises can be suppressed simultaneously. The proposed A-CMF is synthesized and implemented based on the corresponding equivalent circuit model. To achieve a high-efficiency CM absorption at the desired frequency, through the analytical design equations, the values of the model elements are calculated and are all realizable. In this paper, at the operating frequency of 2.4 GHz, the 15-dB suppression level and 96% absorption efficiency are measured, while the size of the A-CMF is merely $8.65 \times 2.5$ mm2. Lastly, we designed two in situ experiments for fully demonstrating the suppression performances of CM-induced radiated noise. The measured results, within the operating frequency band of the A-CMF, show the receiving noise of an antenna nearby can be effectively reduced.