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 (TM
$_{21}$
, TM
$_{02}$
, and TM
$_{31}$
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
$2.238 \,\mathrm{GHz}$
, while using an antenna diameter
$< 7.5 \,\mathrm{cm}$
. Overall, an envelope correlation coefficient
$< 0.01$
is realized between all antenna ports, and a
$360^{\circ }$
field of view AoA estimation is demonstrated across the entire azimuthal plane with mean absolute errors smaller than
$0.098^{\circ }$
. 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.