A 28-Port MIMO Cube for Micro Base Station Applications

A novel multiband, dual-polarized, 28-port multiple-input multiple-output (MIMO) cube is presented. The cube structure enables dense placement of the antennas, whilst still allowing for low correlation between the individual antenna ports. The total size of the cube is roughly 2 × 2 × 0.7 λ₃⁰, where λ₀ is the wavelength at the lowest used frequency. The novelty of the design lies in the use of a combination of orthogonally polarized endfire and broadside radiating antenna elements. Full use of all facets of the cube is achieved without the need to sacrifice bottom or top facets for mounting. Therefore, full azimuthal coverage for communication in two orthogonal polarizations is readily achieved. The system operates in both cellular and Wi-Fi bands (2.4 and 5.5 GHz), with a targeted |S₁₁| below -10 dB. The MIMO performance of the system is evaluated in two environments: the rich isotropic multipath environment and the random line-of-sight environment. These two scenarios represent the edge environments of any real-life propagation scenario in terms of the directional distribution of outgoing or incoming waves at an MIMO transceiver. The intended application of the system is micro base stations and repeaters, with possible extension to massive MIMO.