A 64-element and dual-polarized SICLbased Slot antenna array development qpplied to TDD massive MIMO

Abstract

This research is focused on the development of a 64-elements and dual-polarized slot-based antenna array, fed by a substrate integrated coaxial line (SICL-SAA), with the purpose of reducing mutual coupling in the 26 GHz band. We propose using printed slot antenna array elements on a 0.25 mm thickness Rogers CuClad 233. At the bottom layer, individual cavities are applied for ensuring boresight radiation without compromising the low mutual coupling level among the array elements. An eleven-step design procedure is carried out, reaching on a final numerical SICL-SAA with 1.8-GHz bandwidth, from 25 to 26.8 GHz (6.9%) considering reflection coefficient (S11) lower than -10 dB and a 1-GHz bandwidth for S11 < -20 dB. Experimental results have been shown in excellent agreement with full-wave numerical simulations, demonstrating up to 2 GHz bandwidth from 24.5 to 26.5 GHz for S11 < -10 dB for all array elements. The mutual coupling between adjacent elements is kept lower than -23 dB for the entire bandwidth, envelope correlation coefficient, ECC < -60 dB and the radiating elements provide an 85º beamwidth in both planes (φ = 0° and φ = 90°) and 7.4 dBi gain. Furthermore, a new radiation pattern-based methodology for time division duplexing (TDD) massive MIMO (mMIMO) array evaluation is conceived, which enables to interpret the antenna array coverage and spatial resolution, by inspecting the array resultant multiple beams. Particularly, the impact on the mMIMO spatial resolution is also conducted as a function of the channel correlation, by means of an exclusively radiofrequency approach, i.e. with the advantage of not considering the system-level features. The proposed figure of merit (Λ factor) quantifyies the created multiple beams by the overlapped radiation patterns from mMIMO systems.