The penetration of the field radiated by an indirect ESD into a shielded enclosure through an aperture has been analysed by a new hybrid numerical technique. In fact, the combination of the marching on in time version of the Method of Moment (MoMTD) and the Finite-Difference Time-Domain (FDTD) method allows to study more efficiently and accurately typical EMC problems. In particular, the use of the equivalence principle with a proper set of fictitious currents (accounting for the coupling) permits to divide the complex original problem into two simpler problems: the radiation of the source, analysed by MoMTD, and the field scattering outside and inside the slotted shield, studied by FDTD method. The validation of the model is assessed by setting up an accurate measurement in a well controlled environment using a network analyser. It consists of a monopole on a ground plane, fed by a voltage pulse that radiates a perfectly conducting box with a small horizontal aperture, facing the antenna in its near field region. The numerical results are compared with those from experiment and show a good agreement. Copyright © 1999 John Wiley and Sons, Ltd.
