Compact Beamforming Antennas for Directional Modulation in IoT

The paper discuss a PHY-layer security technique known as Directional Modulation (DM) and its implementations with compact beamforming antennas. The motivation is to allow DM to operate from small and low-complexity IoT devices. While classical DM required large antenna arrays and complex hardware, recent work proposed an alternative algorithm that requires single RF chain. The technique was demonstrated with circular arrays of diameter of 0.6 wavelength, with only one antenna transmitting at each given time. This work revisits the concept and demonstrate its feasibility with multimodal compact beamforming antennas. Unlike circular arrays, for multimodal antennas the directional performance is directly dependent on the number of modes involved and not antenna size – albeit inclusion of higher order modes within limited volume will inevitably lead to the decrease in operational bandwidth and efficiency.