THESIS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Characterization of MIMO Antennas and Terminals: Measurements in Reverberation Chambers

The reverberation chamber (RC) has drawn considerable attention as a multipath emulator over the past decade for both passive and active over-the-air (OTA) tests. This thesis is about RCs for OTA applications. The overview of this thesis is given in Chapter 1. Although the main purpose of this thesis is characterizations of MIMO (multiple-input multiple-output) terminals based on RC measurements, it is of importance to know under which channel condition the device under test (DUT) has been measured. Parameters that are used to characterize the channel in a multipath environment are coherence bandwidth, delay spread, coherence time, Doppler spread, coherence distance and angular spread. In a normal RC, the angular of arrival (AoA) distribution is almost uniform. The corresponding coherence distances for different antennas can be derived readily based on the a priori knowledge of the uniform angular distribution. Therefore, the main tasks of RC channel characterizations are to determine the channel's coherence bandwidth, RMS delay spread, coherence time and Doppler spread. These studies are presented in Chapter 2. For multi-port antennas used in MIMO systems, relevant characterization parameters are correlation, embedded radiation efficiency, diversity gain, and MIMO capacity, all of which can be measured in a RC. In order to compare a RC measurement with that of an anechoic chamber (AC), two methods for evaluations of AC measurement-based maximum ratio combining (MRC) diversity gain and MIMO capacity are presented correspondingly. After examining these two methods, they are applied, respectively, to a wideband multi-port antenna that is measured in both AC and RC. Comparisons show good agreements. Furthermore, a throughput measurement of a LTE (long term evolution) dongle is tested in the RC. A corresponding throughput model is presented. Simple as it is, this model can well predict the measurement result. All of these are studied in Chapter 3. For both passive and active OTA tests, the measurement accuracy is of great importance. Previous RC measurement uncertainty work believed that the RC accuracy depends only on the independent sample number. This thesis, however, shows that the RC accuracy depends not only on the independent sample number, but also on the Rician K-factor, i.e. the power ratio of unstirred electromagnetic (EM) fields to the stirred ones, and that the K-factor represents a residual error in RC measurements. It is also proven using two RCs that accuracy can be improved either by reducing the K-factor or by introducing stirring methods that reduce …