Adaptive Multichannel Terahertz Communication by Space-Time Shared Aperture Metasurfaces

We propose a technique for adaptive multichannel communication in the low-terahertz frequency regime through simultaneous and independent multifrequency multibeam scanning via a single time-modulated metasurface consisting of graphene micro-patch antennas whose Fermi energy levels are modulated by radio-frequency biasing signals. For this purpose, we divide the metasurface aperture into interleaved orthogonally modulated sub-array antennas with distinct modulation frequencies, rendering a shared aperture in space-time. The higher-order frequency harmonics generated by the sub-arrays in such a space-time shared-aperture metasurface are mutually orthogonal as they do not yield an observable interference pattern. A distinct constant progressive modulation phase delay can be adopted in each sub-array to independently scan its corresponding higher-order frequency harmonics via dispersionless modulation-induced phase gradient with minimal sidelobe level and full angle-of-view over a wide bandwidth. The number of sub-arrays and distinct channels can be scaled easily without suffering from cross-talk due to orthogonality of the channels. The concept is established theoretically and verified through numerical simulations. We characterize active beam-scanning performance of the space-time shared aperture metasurface in terms of gain and half power beamwidth and their dependence to the array architecture. We consider both one-dimensional and two-dimensional interleaving for scanning the beams along elevation and azimuth angles. We also obtain the upper bounds for the number of independent channels attainable without compromising angle-of-view as 8 and 64 for one-dimensional and two-dimensional interleaving, respectively within the same physical aperture. Our results point toward high-capacity platforms with low size, weight and power for next generations of terahertz communication systems.