Prediction of Radiated Emission with Transmission Line Model for CISPR 25

Modern automotive ECUs are composed of multitude of microprocessors and other high speed circuits. High speed signals to/from the ECUs for data/control pass through long connecting cable harnesses and generate radiated disturbances on all onboard and off-board electronics. CISPR 25 is standard to control this emission level. However, enforcement of this standard at the post prototype measurement step leads to difficulties in case of failure. Emission is often due to the cable bundle's Common-Mode (CM) current which can be measured easily with current clamps or computed using electromagnetic solvers. In this work, a transmission line based analytical approach is proposed for estimation of Radiated Emission (RE) from an equivalent single cable model emulating the same common mode behavior of a cable bundle. Emission is calculated using the spatial current on the line which in turn are dependent on the terminal impedances. The proposed method is validated with full wave 3D simulation as well as practical measurement. Results show good agreement with a substantially reduced computing resource requirement allowing a quick estimation of the radiated fields.