Predicting the shielding effectiveness of rectangular apertures

A method is described for predicting the behavior of rectangular apertures that makes use of a special transverse electromagnetic (TEM) cell to simulate far-field behavior. Several test apertures of different dimensions (12×12, 12×9, 12×8, 12×6, 12×4, 12×3, 12×2, 12×1.5, and 12×1 in.) were selected to represent the ratios 1:1, 1.3:1, 1.5:1, 2:1, 3:1, 4:1, 6:1, 8:1, and 12:1 in order to test the original assumption that the shielding effectiveness of all of these openings would be represented by the same equation: R_dB=20log(w/2d) where w represents the wavelength of the signal across the opening, d represents the longest dimension of the opening in meters, and R is the attenuation in decibels. A relationship between the ratio changes and the shielding effectiveness was observed as well as a dependence on the polarization of the slot with respect to incident electric and magnetic fields. New models for both polarizations were developed based on the data. The one chosen to represent the worse-case shielding of the apertures is discussed