Improved Transmission-Line Model for a Cable with an Attached Suppression Ferrite

Cable ferrites are noise suppression components acting as a common-mode filter. As was shown in previous publications, such components need to be accurately characterized in terms of their electrical parameters. In this paper these ferrite parameters are used in combination with an analytical transmission-line model, in order to analyze the actual attenuating behavior of the ferrite on the common-mode current within a cable environment, depending on its position and geometry, as well as the termination impedances. The comparison of measurement results for the current distribution along the transmission line up to 1GHz confirms quite well the suggested transmission-line model. As the results for different frequencies show, the attenuation between the noise source and the sleeve may be lower and even substantially negative, as compared to the line section between sleeve and line termination.