We conducted an extensive experimental measurement campaign to quantitatively evaluate the need of intelligent reflecting surfaces for indoor communications above 100 GHz. For this, we deployed the 120-140 GHz front-ends of the TeraNova platform (20 mW of transmission power, 21 dBi transmitter antenna gain, 38 dBi receiver antenna gain, 10 GHz BPSK signal) in a large auditorium and conducted measurements for different Tx-Rx distances and relative orientations.
We designed and numerically modeled innovative hybrid gold/graphene reflect-arrays above 100 GHz. In the proposed design, graphene is utilized to change on-demand the reflection phase/delay of gold-based patch antennas.
- To quantify the required gain for intelligent reflecting surfaces in realistic indoor scenarios and, correspondingly, determine their required size and near- and far-field regions.
- To determine the different operation modes for intelligent reflecting surfaces in the near- and the far-field regions.
- To design a programmable reflect-array architecture that can meet the derived system specifications and support the different needed operation modes.
We demonstrated that, for common indoor scenarios including large meeting rooms and/or auditoria, intelligent reflecting surfaces are expected to provide very large gains, in excess of 30 dB. This is only achieved by increasing the number of elements and total footprint of the reflecting surface. Consequently, the far field distance of the reflect-array easily increase to more than meters. Traditional beamforming strategies are defined for the far field and, thus, different techniques are needed.
Beyond conventional beamforming techniques in reflection, we proposed the adoption of two additional mechanisms to exploit intelligent reflecting surfaces, namely, beam focusing and Bessel beams:
For beamfocusing, the exact position of the TX and RX is required. It is then possible to create a phase transformation that generates a wavefront which converges exactly at the RX position. The required phase shifts are exact conjugates of the individual path distance from each element to the RX. Beamfocusing works particularly well in the near field and provided that the exact RX position is known. Beyond the spot, the beam diverges.
To realize Bessel beams, the aperture can be leveraged to mimic plane waves travelling inwards on a cone. This creates a beam characterized by a non-diffracting central spot along the central axis of the so-defined cone, with concentric rings around it. The power and information carried in each ring of the Bessel beam and the central spot size are the same (with a much greater intensity within the central spot than any of the rings). Thus, even if an obstruction compromises portions of the beam profile, the information and propagation of the Bessel beam remain largely unaffected, which is why these are also referred to as self-healing beams. Moreover, Bessel beams work both in the near field and in the far field.
We have analytically and numerically demonstrated the performance of our proposed hybrid graphene/metal reflect-array and its ability to support the different types of beam fronts explained above, namely, traditional beamforming in the far-field, beamfocusing in the near field, and Bessel beams across distances. Compared to graphene-only reflect-arrays, our proposed solution can generate stronger reflections. Compared to metallic-only reflect-arrays, our solution is the only one that currently supports tunability above 100 GHz.
Publications:
Singh, V. Ariyarathna and J. M. Jornet, “A Plasmonic Array Architecture for Multi-beam Spatial Multiplexing at THz Frequencies,” in Proc. of the 45th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Buffalo, NY, USA, November 2020.