Spatial Characterization of Multi-element Antennas

Licentiatavhandling, 2011

The overall goal of the current thesis is to establish some bases for understanding and characterization of multi-port antennas in a rich multipath environment. Multi-port antennas are the inevitable keystone of multiple input and multiple output wireless communication systems. Due to multidisciplinary nature of the applications of multi-element antennas, they are the subjects of many research groups worldwide resulting in inconsistent nomenclature among them. In this thesis, much effort is expended to look upon this realm of engineering in a unifying approach, with the major stress on electromagnetic aspects of this area. The thesis throws light upon different significant parameters as the key-gauges for characterization of multi-port antennas. We illustrate the dependency of precise measurement of diversity gains upon total number of independent measured samples. Two closed-form formulas are devised rendering diversity gains of two-port antennas in a rich scattering environment. Some examples are presented to verify the accuracy of these formulas. Moreover, received signals at different ports of a multi-element antenna in a multipath environment are the major sources for its assessment. There are certain functions governing the relation between the received signals at different ports of a radiation system and an arbitrary incident electromagnetic wave. The precise derivation of these formulas for different cases of interest are presented in this thesis. Furthermore, it has been frequently acknowledged that in a uniform rich multipath environment the beam-forming technique does not prove beneficial. Here for the first time, we stress that in a uniform non-rich scattering environment, beam-forming technique bestows considerable gain. We demonstrate that the achieved gain in respect to a similar radiation system reduces as the multipath environment becomes richer. In addition to that, it is known that reverberation chambers are the contemporary measurement tools for antenna systems to be used in scattering environments. The shape of these measurement tools plays a significant role in their ultimate performance. We show that rectangular reverberation chambers prove to be more advantageous compared with their cylindrical and spherical counterparts.