Investigation on Grounding Solutions for Shielded Cables by Simple SPICE Models

The aim of the paper is to investigate the performance in terms of immunity of different grounding solutions of shielded cables such as coaxial, twinax and triaxial (doubled screened), by simple SPICE simulations. The cables are modeled by lumped equivalent circuits based on the key parameter of transfer impedance. It is shown that, cascading N electrically short unit cells of the cable, it is possible to obtain the same accurate results of a distributed model, valid without limit in frequency, for the frequency range of interest. The advantage of this approach is that these circuit models are suitable for both frequency and transient simulations. They can be easily implemented in the latest generation of commercial SPICE-like simulators with minimum effort, and the simulations run in very few seconds. The accuracy of the models is validated by comparison with measurements, with the results obtained by a full-wave 3D software and other methods. Some practical grounding cable structures are simulated and guidelines are given.