Fast and accurate intermediate-level modelling approach for EMC analysis of enclosures

Intermediate-level circuit models use circuit models containing transmission lines to represent the waveguide modes in an enclosure. The coupling of electromagnetic fields to contents, and apertures is achieved by the use of circuit approximations. Typical models run in a few seconds on a personal computer, compared with many hours, or even days, required for full-wave simulations of the same problem. This efficiency allows the intermediate-level models to be used in situations where the time and effort involved in full-wave simulations would be prohibitive. The technique is reviewed, discussing both its relation to full-wave simulations and the type of problems for which it is a particularly appropriate tool. Example applications to the prediction of the immunity of a generic missile (GENEC) are given, based on extensions of the model to enclosures with a circular cross-section. The models have been validated by measurements on GENEC and comparison with other simulation techniques. A coupling model has also been developed for small apertures in the sidewall of the waveguide using aperture polarisability theory. The results demonstrate that excellent agreement with measurements can be obtained at frequencies up to 3 GHz.