In this article, a compact 3D beam-steering MIMO antenna operating at 5.75 GHz is proposed for on-body Internet of Things (IoT) applications. The planar antenna comprises a central patch and two concentric annular rings. The theory of spherical modes is used to discuss the beam-steering concept, where the free space measured beam-scanning covers the entire xy-plane, while a 44° range is realized in xz and yz-planes. The on-body performance is tested using a multi-layer phantom, and the measured peak realized gain is 6.41 dBi. The antenna is characterized by compact size (0.77λ), low profile (0.03λ), specific absorption rate below the established limits, good efficiency and 3D beam-steering characteristics while operating in an on-body setup. Therefore, the proposed solution can enable advanced wireless applications like localization and physical layer security in emerging size-constrained on-body IoT devices.

This article studies security aspects of data transmission in on-body Internet of Things (IoT) devices through the use of Directional Modulation (DM) from a smart watch integrated antenna. DM is a beamsteering-based Physical Layer Security (PLS) method used to transmit baseband constellations to known secure locations, while simultaneously scrambling them in other directions. However, in the state-of-the-art DM is implemented using large arrays, which are out-sized for many on-body IoT devices. To overcome this challenge, this study proposes multimodal ultra-thin compact antennas suitable for integration into smart watches. These antennas present advanced beamsteering capabilities that allow the implementation of DM from a low-thickness structure of up to 0.57 mm or 1/100th of wavelength at the center operating frequency. Two different DM implementations (simultaneous multiport transmission and an energy-efficient single-port transmission) are tested using a multi-layer phantom. Overall, secure steerable transmissions are realized, and experimental verifications are carried out to validate the proposed concept. Ultimately, this article demonstrates the feasibility of applying new energy-efficient and low-cost security techniques to enhance the privacy of resource-constrained IoT devices.Â

This work proposes a small dual-band (2.4 GHz and 4.89 GHz bands) 3D beamforming Multiple-Input Multiple-Output (MIMO) antenna for emerging size-constrained Internet of Things (IoT) applications. The performance is realized via digital beamforming in a structure sized only 51.5 mm in diameter (smaller than half wavelength at 2.4 GHz). At the 2.4 GHz band, the antenna realizes an isolation > 30 dB, and the Envelope Correlation Coefficient (ECC) is < 0.0003), with a bi-directional beamforming capability in the azimuth plane and unidirectional beamforming across the elevation plane. At the 4.89 GHz band, the isolation is > 19 dB, and the ECC< 0.0047, while unidirectional beamforming is achieved in both the azimuth and elevation planes.Â

This work proposes a small pattern and polarization diversity multi-sector annular antenna with electrical size and profile of ka=1.2 and 0.018lambda, respectively. The antenna is planar and comprises annular sectors that are fed using different ports to enable digital beamforming techniques, with  efficiency and gain of up to 78\% and 4.62 dBi, respectively. The cavity mode analysis is used to describe the design concept and the antenna diversity. The proposed method can produce different polarization states (e.g. linearly and circularly polarized patterns), and pattern diversity characteristics covering the elevation plane. Owing to its small electrical size, low-profile and diversity properties, the solution shows good promise to enable advanced radio applications like wireless physical layer security in many emerging and size-constrained Internet of Things (IoT) devices.