Influence and benefits of stray magnetic couplings in EMC filtering

The transfer function of an EMC (Electo-Magnetic Compatibility) filter can be strongly disturbed in high frequency (HF) due to all the magnetic and electrostatic imperfections. Some of them are specific to the discrete component geometry, and the others comes from stray couplings between every element of the system (as tracks well as components themselves). Theirs influences on an EMC filter response will be pointed out at first. Given that these phenomena have been commonly neglected so that to be able to easily describe the behaviour of a system, it was essential to have them as low as possible in order to have the real filter response the closest to the theoretical one. It is however possible to use them in order to improve the behaviour of the system instead of deteriorate it in high frequency. But this necessitates defining a complete analytical model where all the components appear, no one neglected. With this new modelling, other building guidelines could be given so that to have the best filter response that it is possible to have. This paper will then propose this analytical model.