Spherical wave theory applied to mobile radio channel modeling, synthesis and emulation

The future mobile communication systems will provide increasing data rates to satisfy the service requirements of the users. This means that the radio performance of especially the mobile terminals becomes more important and has to be as good as possible. Thus, it is very important to be able to evaluate the performance of the antennas of the mobile terminals in a realistic way. This thesis deals with practical and theoretically justified ways to describe both the field environment and the radiated fields of mobile terminal antennas and antenna systems using spherical wave theory. In this thesis, advanced measurement methods that facilitate the radio wave propagation channel as well as mobile terminal antenna characterization are developed. The research in this thesis contributes to three key areas: (1) channel-independent antenna characterization and performance assessment, (2) degrees-of-freedom (DoF) of propagation channels and (3) over-the-air (OTA) testing. In the first part of this thesis, theoretical considerations of the spherical wave expansion (SWE) for the antenna array configuration on the cubical surface for estimating the propagation channel and measuring the antenna radiation through a near-field to far-field transformation (NF-FF) are studied. A novel technique, azimuthal mode decomposition (AMD) for the reduction of the computational burden is presented for both applications using the cubical array configuration. In second part, the proposed antenna configuration is applied to the estimation of the degrees of freedom (DoF) in spatial multipath channels. In multi-antenna systems, such as multiple-input multiple-output (MIMO), multiple-input single-output (MISO), this DoF provides the number of antenna elements on the aperture for efficiency improvement of the system performance by utilizing the spatial transmission, e.g., diversity and multiplexing. In the third part of this thesis, multi-probe based MIMO over-the-air (OTA) testing is described for the performance evaluation of multi-antenna systems. The related uncertainties of such testing, for instance, the required number of probes, optimum probe placement and the influence of the probe polarization are investigated in theory and practice.