How RF Anechoic Chambers Work

By Dr. Glen Dash, Ampyx LLC

A radio frequency "anechoic chamber" is a shielded room whose walls have been covered with a material that scatters or absorbs so much of the incident energy that it can simulate free space. Its origins can be traced to efforts to build aircraft which absorbed or scattered radar signals during the Second World War. Recent innovations, such as the use of ferrite tiles, have greatly enhanced performance of these chambers.

Anechoic chambers may seem to operate through a bit of black magic, but the analysis of how they work is really quite straightforward. Assume for a moment that an electromagnetic plane wave (free space impedance = 377 ohms) strikes a wall at normal incidence. This can be modeled as a signal passing down a transmission line with a 377 ohm characteristic impedance.