Radiated emission of automotive communication bus systems caused by mode-conversion of common-mode chokes and in-line-connectors

The following study describes the mode-conversion of common-mode-chokes and in-line-connectors and their impact on radiated emissions of automotive communication bus systems. The main focus of the article lies on on the analytic description of the mode-conversion induced by automotive inline-connectors (including the untwisted lines before and after the in-line-connector), as compared to the mode-conversion of typcial common-mode chokes used for the considered differential bus systems. Analytical results thereby are compared in detail to results obtained by numerical modelling as well as to measurement results for a 100 MBit/s automotive Ethernet-system. It is shown, that the emission within the frequency band of the information signal strongly depends on the level of mode conversion. For automotive high speed bus systems like the 100 MBit/s Ethernet system investigated in this article, this leads to a significant emission in case of state-of-the-art common-mode chokes and in-line-connectors used nowadays. It is shown, that the analytical description and modelling of (assembled) in-line-connectors covers all of the key parameters in order to reliably predict mode-conversion and therefore radiated emission.