Dual-Band Beam-Steering Antenna for Physical Layer Security in Small IoT Devices

This work proposes a dual-band antenna for enhanced physical layer security directional modulation technology in small Internet of Things (IoT) platforms. The design is a stacked-patch structure with λ/2 diameter and λ/10 profile, where λ is the wavelength at the lower band. The cavity model analysis is used to describe the antenna's dual-band capabilities, demonstrating a measured -10dB impedance bandwidth of 10MHz, isolation >13.5dB, and peak realized gain of 5.6dBi at the lower band, i.e. 2.7GHz; these values, respectively change to 50MHz, 14dB, and 5dBi for the upper band (5.48GHz). By exploiting the phase properties of the proposed structure, unidirectional beam-steering is realized across the entire horizontal plane at the antenna's two operating bands. This performance is investigated to realize dynamic dual-band DM, revealing that secure steerable transmissions are performed with a very low Bit Error Rate (BER) of 10-5 in the desired receiver directions. At the same time, high errors are observed in other undesired directions. Owing to the antenna's compact size, low profile, dual-band beam-steering properties, and very low BER, the method is proposed as a good candidate to leverage the dual-band characteristics and provide improved security to emerging resource-constrained IoT devices.