Comparison of analytic, numerical and approximate models for shielding effectiveness with measurement

The authors present a comparison between different estimates of the shielding effectiveness (SE) of cavities containing apertures and predictions made using a rigorous variational solution. Although the rigorous solution is computationally intensive, the method can be used as a standard against which more practical approximations, numerical methods and laboratory measurements can be compared. SE predictions from three methods are compared to the rigorous solution. These are: electromagnetic time domain modelling using the transmission line modelling (TLM) method, experimental measurements in a screened room, and an approximate solution based on the interaction of the lowest order waveguide mode and the aperture field. These comparisons of shielding effectiveness evaluations were made for a rectangular cavity with a range of aperture sizes and for frequencies in the range 200 MHz to 1.0 GHz. The results show that the measurements compare well with the rigorous solution, time domain simulations have a relatively long computation time and may still have noticeable discrepancies while the approximate solutions are computationally very efficient but may be significantly in error in particular for observation points close to the aperture.