Estimating radiated emissions from microstrip transmission lines based on the imbalance model

Common-mode current traveling on peripheral cables can be a major source of radiated emissions and a potential electromagnetic compatibility (EMC) hazard. Models and tools for early prediction of common-mode current proved extremely useful for EMC engineers. Imbalance difference model has been one the most successful common-mode modeling techniques in EMC literature. It has, however, been only validated at the low EMC frequency range below 1 GHz. In this work, detailed mathematical analysis that employs transmission line theory along with the imbalance model is presented. The limitations of the imbalance model are explored and discussed. The validity of the model is extended to a higher frequency range, under certain operating conditions. Finally, closed-form expressions for estimating common-mode electric-field are introduced, offering the possibility of replacing complex full-wave simulations.