Efficient Modeling of Mutually Coupled Array Antennas for Massive MIMO Applications

This thesis focuses on the development of computationally efficient techniques for modeling the effects of mutual coupling (MC) in finite antenna arrays with the focus on massive multiple-input multiple-output (MIMO) base station antenna (BSA) applications. Several techniques have been analyzed: (i) iterative methods enhanced by the characteristic basis function method, (ii) hybrid alternating Anderson-Richardson iterative approach and (iii) iterative approach which is based on the simulated far-field data of an isolated antenna element (feed-point and plane-wave excitations). Here, (i) and (ii) represent the iterative solution techniques applied to a classical linear system which arises from the analysis of an antenna array in the context of the method of moments (MoM). In contrast to (i) and (ii), (iii) represents the nonclassical (field-based) iterative solver in which the interelement MC interactions are approximated as a pair of plane waves with mutually orthogonal polarization taken from the spherical wave expansion of the field scattered from other elements. Since these plane waves can be matched straightforwardly to the simulated data of an isolated element, the interaction process is computationally inexpensive and, consequently, the orders-of-magnitude runtime savings in comparison to commercially available MoM-based solvers can be achieved by using this approach. In addition to the development of computationally efficient strategies for modeling MC effects, the impact of MC on the performance of massive MIMO systems, has been analyzed. To this end, a sum-rate model of a downlink line-of-sight (LoS) multiuser MIMO system in the presence of MC effects, has been developed. Herein, the effects of MC are accounted for through the S-matrix of the BSA and the embedded element patterns of all BSA elements, which are used to approximate the channel matrix in a LoS environment. The results obtained by using this model in the context of different BSA array configurations show the degradation of the sum rate that can be achieved by using closely spaced BSA array configurations and, consequently, demonstrate the essentialness of proper modeling and inclusion of physical antenna effects in the models of massive MIMO systems.

Publication year:2021

Accessibility:Open