OTA measurements of wireless stations in reverberation chamber versus anechoic chamber: from accuracy models to testing of MIMO systems

The paper will describe the fundamental characteristics of different wave propagation environments (such as Rayleigh fading, Rice fading, and polarization balance; coherence bandwidth and time delay spread; and fading speed, coherence time and Doppler spread), and relate these characteristics to the Line-Of-Sight (LOS) emulated by good anechoic chambers, and the rich isotropic multipath environment emulated by good reverberation chambers. The conclusion is that the reverberation chambers mean the same to Over-The-Air (OTA) testing of antennas for use in multipath environments as anechoic chambers do to antennas for free-space-like environments. They enable a unique, objective and repeatable antenna characterization that cannot be achieved in other environments. Thereby, the reverberation chambers and anechoic chambers complement each other perfectly. The paper will also give examples showing that the performances of three different types of incremental antennas are very different and depend strongly on their orientation when they are located in a 2-D horizontal multipath environment with incoming waves only in the horizontal plane, whereas their performances are equal and invariant to orientation when they are located in a rich isotropic multipath environment as emulated by a reverberation chamber. The paper also summarizes how the reverberation chamber during the last ten years has been developed to an accurate tool to determine the performance characteristics of complete wireless terminals, stations and systems both for the transmitting case (total radiated power) and the receiving case (total isotropic sensitivity and average fading sensitivity), and when the stations are provided with antenna diversity and MIMO (Multiple Input Multiple Output) capability.