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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {2.34}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {5.65}$ </tex-math></inline-formula> GHz bands, with a diameter smaller than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\lambda /2}$ </tex-math></inline-formula> and a profile of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\lambda /100}$ </tex-math></inline-formula>, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\lambda }$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {0.275^{\circ }}$ </tex-math></inline-formula> is realized in the free space case, increasing to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {0.52^{\circ }}$ </tex-math></inline-formula> 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.