An unbiased data sheet
This data sheet if for high frequency pyramidal lined anechoic chamber, for low frequency fully anechoic chambers see EMC ferrite lined variants.
The function of a fully anechoic chamber is to copy free space, that is, to have zero reflections from the test chamber walls, of course zero is not possible but as close to zero is the aim.
The size of the pyramidal absorber is relative to the frequency and the amount of accuracy specified (how close to zero reflections) The performance is normally defined inside a quiet zone (QZ) this can be a measurement cylinder or sphere.
For lower frequencies and higher performance larger pyramid absorbers have to be used because the performance of a pyramidal absorber is relative to the wavelength,
A 30cm pyramidal absorber @ 1GHz (30cm wavelength, thus 1 x wave) will give c30dB of return loss (reflection quietness)
A 90cm pyramidal absorber @ 1GHz (3x wavelength) will give >50dB of return loss At 10GHz the wavelength is only 3cm so 3x wave is only 90mm
There are unavoidable bad things inside a fully anechoic chamber:
These things need to be considered so that the bad effect is minimised
The test is actually a reflectivity test called a VSWR (Voltage Standing Wave Ratio) The test searches for reflections from the wall by moving the receive antenna longitudinally and laterally in the chamber, this is normally done on plastic rails. There are specialist test companies that can do this work
