A fast multiple mode intermediate level circuit model for the prediction of shielding effectiveness of a rectangular box containing a rectangular aperture

This paper presents an intermediate level circuit model (ILCM) for the prediction of the shielding effectiveness (SE) of a rectangular box containing a rectangular aperture, irradiated by a plane wave. The ILCM takes into account multiple waveguide modes, and is thus suitable for use at high frequencies and/or relatively large boxes. Inter-mode coupling and reradiation from the aperture are taken into account. The aperture may be positioned anywhere in the front face of the box, and the SE at any point within the box may be found. The model is presented in such a way that existing ILCM techniques for modelling elements such as monopoles, dipoles, loops, or transmission lines may be seamlessly incorporated into the circuit model. Solution times using the ILCM technique are three orders of magnitude less than those required by traditional numerical methods such as FDTD, TLM, or MoM. Accuracy however is not significantly compromised. Comparing the circuit model with TLM over nine data sets from 4 MHz to 3 GHz resulted in an rms difference of 7.70 dB and mean absolute difference of 5.55 dB in the predicted SE values.