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

Abstract

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. The current distribution on the arms of the dipole antenna are made asymmetric by the balun, which changes the relative phase between the feed currents. By rapidly switching between two mirrored states, the relative phase shift changes sign, causing the current distribution to manifest asymmetrically on the arms of the dipole antenna. The resultant far field radiation pattern is therefore asymmetric in both states, but mirrored between the two states. 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 black box 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.