Pyramid absorbers are available in sizes (lengths) of 100 mm to 2.500 mm. The
required length depends mainly on the wavelength of the lowest usable frequency specified for the anechoic chamber. The length decreases with increasing frequency. Pyramid absorbers of a size of >= 2.000 mm are mainly used in chambers with measuring distances of up to 10.0 m where the requirement for NSA correlation of better than +/- 4 dB has to be fulfilled from 30 MHz to 1 GHz. In tests with frequencies starting at 80 MHz (e.g. in immunity tests according to IEC/EN 61000-4-3) the respective requirements can be fulfilled already with a pyramid length of 75 cm. For measurements in the range >= 1 GHz, even sizes of 200 to 300 mm are sufficient. Compared to ferrite absorbers, the pyramid absorbers offer the considerable advantage of lower price (depending on size), lower weight and their practically unlimited use up to the high GHz range.