A Dipole Antenna With a Dynamic Balun for Wireless Security via Amplitude-Based Directional Modulation

We present a new approach to secure wireless operations using a simple dipole antenna with a dynamic unbalanced feeding structure. By rapidly switching between two states, a dynamic radiation pattern is generated, resulting in directional modulation. Common-mode currents are excited by the unbalanced feeding structure, causing an asymmetric complex radiation pattern. In this work, the asymmetry manifests only in the amplitude of the radiation pattern. A mirrored feeding structure creates two states that mirror one another in angle. Consequently, rapid switching between the two states results in a far-field pattern that is dynamic in amplitude at all angles except for a narrow region of space, which is referred to as the information beam. The dynamic radiation pattern causes additional modulation on any transmitted or received signals, thereby obscuring the information at all angles outside the information beam. The proposed directional modulation technique is separate from both the antenna and the rest of the wireless system, and can thus be implemented in a modular form in wireless communications or sensing systems. We demonstrate the concept in a 1.86 GHz-printed dipole antenna, demonstrating the transmission of 256-QAM signals.