Induced fast transients in multiconductor shielded cables

The coupling of fast transient electromagnetic fields to lossy multiconductor shielded cables is considered. Calculation of the transient responses calls for the development of models simulating the cable, the incident field and the impressed sources. Accurate models are developed to simulate a multiconductor cable with a multilayer braided-shield and multiple parallel inner conductors or twisted-wire pairs. The incident field is the sum of the primary field, represented as a plane wave, and the wave reflected from the ground. The cable response is obtained in the frequency domain by means of an efficient matrix procedure, based on the transmission-line theory, which involves Thevenin-equivalent representation. The transient waveforms for any terminal load condition are computed by an inverse discrete Fourier transformation. The theoretical procedure is applied for evaluating transient voltages and currents induced by an EMP source on a bifilar twisted-wire line, with and without shield, above an aluminium or a ground plane.