Pre-compliance test method for radiated emissions with multiple segment transfer functions

Radiated emission testing of electric components, modules and systems is mandatory. Such tests are performed during the development process. Due to strict time schedules and limited access to EMC measurement facilities, fast applicable pre-compliance methods are needed. Early knowledge of a product´s EMC performance is indispensable for the developer to initiate required measures immediately. This is directly correlated to overall cost reduction. This paper deals with a pre-compliance test method for radiated emissions. The method is adapted to the CISPR 25 standard for automotive components and modules. Here, a setup is defined including equipment under test connected via a cable harness to a load. The site of operation is the developer´s laboratory setup. Common mode currents on the cable harness are used to predict the radiated field strength occurring in an absorber-lined shielded enclosure. Therefore, multiple transfer functions are generated with a vector network analyzer in an absorber-lined shielded enclosure. Those transfer functions represent the correlation between common mode current segments in the defined test setup environment and their electric field strengths. Current probe measurements outside a test chamber along the cable harness of the equipment under test in combination with those transfer functions lead to a prediction of the radiated emissions. The multiple segment transfer functions method will be described and applied to practical real test setups.