Design of Absorber-Lined Chambers for EMC Measurements Using a Geometrical Optics Approach

Absober-lined chambers (ALC´s) have been found useful for EMC measurements over an extremely wide frequency range. However, only limited information about the field structure inside ALC´s can be efficiently determined by measurements, while the characteristics of the rough absorbing surface do not render their analysis amenable to formal methods. The computation of field structure as a function of various parameters must thus resort to empirical modeling. A simple computational technique presented here predicts fields inside ALC´s to a good approximation. Use is made of the Geometrical Theory of. Optics (GO). The absorber material is empirically modeled by its reflectivity as a function of frequency and angle of incidence. To establish the validity of the technique, computed results are compared to measured data. The methodology is then extended to compute fields inside a variety of ALC configurations. A study of the effect of shape, size, and absorber characteristics on these fields is presented to demonstrate the utility of the technique as a tool for ALC design purposes.