Load modulated arrays: a low-complexity antenna

This article describes promising recent progress in the area of massive antenna array architectures with low front-end hardware complexity. The presented technology enables the design and implementation of antenna arrays with large numbers of elements, while obtaining significant front-end hardware savings as compared to the conventional solutions. This newly appearing design approach could be used in order to design either massive arrays with complexity that would be prohibitive with the current technology, or smaller arrays that offer high spatial degrees of freedom and are suitable for future small yet powerful cell nodes. RF hardware architectures with a single RF chain are reviewed, compared, and found superior to conventional MIMO implementations in terms of cost, dissipated heat, and physical size. The proposed improvements on the RF side allow the merging of the two dominant cellular technologies of virtual (distributed) and massive (centralized) MIMO into a hybrid approach of antenna arrays that is suitable for both large base stations and small (possibly cooperative) units such as remote radio heads.