Exploiting Multimode Antennas for MIMO and AoA Estimation in Size-Constrained IoT Devices

This work proposes compact multimode Multiple-Input-Multiple-Output (MIMO) antennas for Angle of Arrival (AoA) estimation in miniaturized Internet of Things (IoT) systems. The method excites different orthogonal radiating modes (TM21, TM02, and TM31 modes) for beamforming capabilities, and the AoA performance is investigated using the Multiple Signal Classification (MUSIC) algorithm, executed using numerical and experimental data. The technique is tested at 2.238 GHz, while using an antenna diameter < 7.5 cm. Overall, an envelope correlation coefficient < 0.01 is realized between all antenna ports, and a 360 degrees field of view AoA estimation is demonstrated across the entire azimuthal plane with mean absolute errors smaller than 0.098 degrees. Furthermore, it is shown that the capability of separating multiple simultaneous impinging signals is comparable to that of state-of-the-art circular arrays with similar number of RF transceivers, while offering, respectively, up to 35% and 71% antenna diameter and height miniaturization.