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.