Evaluation of reflectivity level of anechoic chambers using isotropic, 3-dimensional probing

This paper describes an experimental technique for evaluating anechoic chamber reflectivity utilizing a new NBS isotropic probe mounted on a polyfoam track and support structure designed for probing the chamber\´s quiet zone in all three orthogonal planes. The probe is omnidirectional within dB and has sufficient sensitivity to permit evaluation of reflectivity levels as low as 59 dB. It can be used from 150 MHz to 10.0 GHz. Complete scattering information is obtained without applying a receiving antenna pattern correction with only 3 orthogonal scans per frequency required. The paper presents a brief treatment of the theory involved, a description of the system and measurement technique employed, and a discussion of typical measurement results.