A Dual-Band Planar Antenna for Angle-of-Arrival Estimation in On-Body IoT Devices

This article proposes a planar dual-band beam-steering compact antenna for Angle-of-Arrival (AoA) estimation in on-body Internet of Things (IoT) devices. The antenna operates at $\boldsymbol {2.34}$ and $\boldsymbol {5.65}$ GHz bands, with a diameter smaller than $\boldsymbol {\lambda /2}$ and a profile of $\boldsymbol {\lambda /100}$ , where $\boldsymbol {\lambda }$ is the wavelength at the lower band. The spherical modes theory is used to discuss the beam-steering and dual-band characteristics, demonstrating continuous beam-scanning performance across the entire horizontal plane. These properties are then studied to realize AoA estimation, where the performance is tested in free space and with a multilayer phantom. Overall, it is demonstrated that a measured peak error of $\boldsymbol {0.275^{\circ }}$ is realized in the free space case, increasing to $\boldsymbol {0.52^{\circ }}$ for the on-body setup. Owing to its small size, ultralow profile, advanced beam-steering characteristics, good on-body performance, specific absorption rate values below the established limits, and dual-band operation, the proposed technique is expected to find favorable applications in many emerging on-body IoT devices.