Characterising the quiet zone of an anechoic chamber

For accurate measurements, it is important to know the size and quality of the quiet zone of an anechoic chamber. It is also important to know the approximate direction from which the worst reflections come. The standard way to determine this is by means of a free-space VSWR test, which involves scanning a medium gain horn within the required region of the chamber. This method is practical for anechoic chambers with large dimensions in wavelengths, but where small chambers with dimensions of only a few metres are used at low frequencies, the horn dimensions become restrictive. Moreover, the scanned region becomes electrically smaller and inverting the recorded data back to the sources of reflection is more challenging. This paper explores some different methods using smaller antennas.