Absolute Security with Multiple-Slit Diffraction in Terahertz Communication Links

Abstract

Many widely used antennas in terahertz (THz) directional communications (including horn antennas) are not fully compatible with the recently proposed absolute security approach due to the absence of strong frequency-dependent minima in the intrinsic antenna pattern. To this end, we propose to use a multiple-slit aperture to modify these non-suitable radiation patterns in a non-intrusive manner. Based on the principle of diffraction, the multi-slit aperture creates frequency varying minima critical for absolute security. We show that improved security performance, quantified by the size of the secure region in space (termed blind region), can be achieved by employing a wider diffraction aperture with a wider slit opening. We further characterize how the non-uniform wavefront, which is typical in practical transmission and results in varying amplitude and phase at different slit openings, affects the size of the blind region. This diffraction-based scheme is experimentally demonstrated with a horn antenna operating near 200 GHz. We demonstrate that, while the intrinsic horn antenna yields no blind region for angles within 16° from the intended user, the modified antenna configuration produces strong minima sufficient to create blind regions at angles as small as 4° and an expanding blind region with increasing transmission bandwidth, thus validating the security gain with this approach.