Reverberation Chamber Characterizations for Passive and Active OTA Measurements

Licentiate thesis, 2010

Reverberation chamber (RC) has drawn more and more attention as a multipath emulator over the past decade. It has been used for antenna efficiency measurements. It has also been used to measure diversity gain and multi-input multi-output (MIMO) capacity using multi-port antenna. Apart from the passive measurements mentioned above, RC is able to measure active device, such as total radiated power (TRP) and total isotropic sensitivity (TIS) for mobile phone, throughputs of wireless local network (WLAN) system, and so on. All these measurements can be called over-the-air (OTA) measurements. For active OTA measurements, it is of importance to know under which channel condition the bit error rate (BER) is measured. Parameters that are used to characterize channel in multipath environments are coherence bandwidth, delay spread, coherence time, Doppler spread, coherence distance and angular spread. To determine any of these parameters involves channel sounding. In a normal RC, angular of arrival distribution is almost uniform. The corresponding coherence distances for different antennas can be derived at ease based on the a priori knowledge of uniform angular distribution. Therefore, the task of channel sounding in RC is to determine coherence bandwidth, RMS delay spread, coherence time and Doppler spread. These are studied in papers [A-C]. For passive small single-port antenna measurements, radiation efficiency and mismatch factor are of interest. For multi-port antennas used in multipath environments, correlation, embedded radiation efficiency, diversity gain and MIMO capacity, which are usually used to characterize diversity and MIMO performances of the multi-port antennas, are of interest. All of these can also be measured in RC. Papers concerning these are [D-F]. For active OTA measurements, we need to have an accurate estimation of the power level (path loss) of the RC. For radiation efficiency measurements, the accuracy of the power levels directly determines the accuracy of the measured efficiency. Therefore, it is important to characterize the accuracy of the average power transfer function measured in RC. The average power transfer function is basically power transfer function averaged over all samples. A large number of independent samples ensure good accuracy. However, the maximum number of independent samples for a RC is physically limited by the shape and size of the RC, and the mode-stirrers inside the RC. Thus, the aim of this work is to improve the RC’s accuracy. Papers [G-H] are about this work, of which Paper G describes how the direct coupling between transmit and receive antennas causes a residual error that is strongly affected by the loading of the chamber.