This invention relates generally to the field of anechoic chambers.  More specifically, this invention relates to a dual-chambered anechoic chamber used in conjunction with spatial averaging for making transmission measurements of electromagnetic devices. 
Large anechoic chambers are used to perform transmission measurements.  Building space requirements contribute to the high construction costs of these large chambers, limiting their availability.  Box anechoic chambers, which are limited by the box shape and the shape of the aperture, are a less expensive alternative to the large chambers.  Enlarging the chamber and thickening the absorber material can achieve increased performance of box chambers, but cost remains a factor. 
Thus, there is a need for a relatively small anechoic chamber, which provides accurate transmission measurements without the high costs associated with larger anechoic chambers.