Common-mode currents generated by circuits on a PCB-measurements and transmission-line calculations

Common-mode (CM) currents on cables attached to printed circuit boards of various complexity have been measured. The boards have a continuous ground plane, with tracks on both sides. The experimental results are compared to calculations with a transmission-line (TL) model. Expressions for the coupling parameters in the TL model have been derived with conformal transformations and the method of moments. Measurements up to 1 GHz agree with the TL model, showing that this model can be used as a tool for an early EMC analysis during the lay-out and routing of a board.