Pre-compliance test method for radiated emissions of automotive components using scattering parameter transfer functions

Radiated emission tests for automotive components according to CISPR 25 are used monitoring their electromagnetic compatibility. Due to parallelization of single work packages schedules are rather strict for component development and tests. Time for first EMC tests of prototypes and their delivery is getting short. Knowledge of EMC properties is important for the developer to initiate measures as soon as possible. An early estimation of radiated emission is directly connected to cost reduction. Hence, pre-compliance test methods become more and more important. This paper presents a pre-compliance measurement approach which is capable to predict the radiated emission with regard to the CISPR 25 standard. Site of operation of this prediction technique is the developer´s laboratory setup without the need of an expensive semi anechoic chamber. The method uses the correlation of common mode currents on cable harnesses and the radiated field strength. Common mode currents on harnesses are assumed to dominate the radiated field in the frequency range up to 200 MHz. Common mode currents are measured with current probes. A recorded transfer function in combination with current probe measurements leads to an estimation of the radiated field. Transfer functions are obtained using scattering parameter measurements performed with a network analyzer. The transfer function will be described, analyzed and its applicability for field estimation will be shown by a case study.