Distributed Antenna Array Dynamics for Secure Wireless Communication

We demonstrate a new approach to implementing directional modulation that leverages distributed array dynamics to change the antenna array pattern over time. With appreciable spacing between the elements, the spatial phase pattern varies rapidly, such that small physical motions result in large phase variations. We define an average radiation pattern that characterizes the space-time modulation of the array pattern and calculate a spatial information filter based on the additional modulation imparted on transmitted data. The concept is demonstrated experimentally using a two-element 1.5 GHz transmit array with relative motion between the elements. The array consists of two nodes, each with one dipole antennas transmitting BPSK data, and each with two log-periodic antennas used to estimate the relative separation of the nodes and correct the beamsteering phase of the transmitters. The node separation is varied dynamically over a range of 0.98λ – 4.7λ. We investigate the use of linearly- and sinusoidally-varying internode dynamics, and demonstrate a low bit-error-ratio of approximately 10-5 at the desired transmission direction, indicating high throughput, and a high error ratio of approximately 10-0.3 at angles outside of the mainbeam, indicating corrupted data, at a signal-to-noise ratio of 12 dB.