On the Keyhole Effect in Over-The-Air Testing of Higher Order MIMO Systems

In this paper, the influence of a limited number of radio frequency connections between two Rayleigh fading environments, also known as the keyhole effect, is theoretically investigated for higher-order MIMO systems. It is shown that the effect of a limited number of keyholes is kept stable or is even reduced as the number of keyholes is equal to or larger than the MIMO system order. The results are relevant for over-the-air testing with connected Rayleigh fading systems, such as a channel emulator connected to a reverberation chamber, or a reverberation chamber connected to another reverberation chamber (nested reverberation chambers).