Predicting Radiated Emissions from a Complex Transportation System Wiring Harness

Abstract

Low frequency radiated emissions problems are often caused by common mode currents flowing on wiring harnesses. The ability to predict radiated emissions problems early in the design process can save both time and money and result in a better product. Methods have previously been reported for rapidly characterizing common-mode sources driving a harness and then using these equivalent sources to predict radiated emissions. These methods are extended in the following paper to predict radiated emissions from a complex 32-wire harness bundle connected to an engine control unit. Rapid experimental characterization of the common mode sources is enabled using an equivalent cable bundle approximation of the original harness, where wires with roughly equivalent source and load impedances are lumped together and treated as a single equivalent wire. Sources driving the equivalent bundle were found using a specialized measurement fixture. Only a few measurements are required, even if there are many wires associated with the source and they originate at different ports on the component. Full-wave models of the equivalent harness were built and along with the equivalent source were used to predict radiated emissions. This model was able to predict radiated emissions from 20–300 MHz with reasonable accuracy, with peak emissions typically predicted within about 6 dB of measurements, when using multiple different harness lengths and routings.