Reflectivity level of anechoic chambers at 183 GHz

The reflectivity levels of the anechoic chamber of the Helsinki University of Technology and the two chambers of the Technical Research Centre of Finland were measured at 183 GHz. Typical values of the reflectivity level of the tested chambers at 183 GHz are below -50 dB at moderate azimuth angles (<50 degrees ) and -45 dB at large angles ( equivalent to 90 degrees ) measured with 20 dB standard gain pyramidal horns. A reflectivity level of -50 dB corresponds to a measurement accuracy of +or-0.25 dB at a radiation pattern level of -19 dB. The maximum backwall reflection in the three chambers is about -28 dB. The size of the pyramids does not have a significant effect on reflectivity. A more important factor is the geometry of the chamber. The quality of absorbers degrades significantly as frequency increases.<>