Prediction of radiated emissions from cables over a metal plane using a SPICE model

A method for creating a simple SPICE model is proposed such that the SPICE model allows prediction of radiated emissions in component level tests, such as those specified by CISPR 25 and MIL-STD 461. The model predicts measured emissions when the antenna is in the vertical direction, where emissions are typically worst for such geometry. It is shown that the radiation from the ground connections between the cables and return plane dominates over the radiation from the horizontal cables. The currents in these ground connections are predicted by treating the cables above the return plane as transmission lines and by treating the ground connections as infinitesimal radiating dipoles. The electric fields generated by these infinitesimal dipoles are summed at the antenna, where the antenna factor is then used to predict the received voltage at the antenna. Test results show that this SPICE model is able to predict peak emissions within a few dB over a range from 60 MHz up to 1 GHz for a variety of circuit configurations. This model should help circuit designers to better evaluate the design of their components early in the design process and help them to better understand the mechanisms behind emissions problems.