Memristor-Based 1-Bit Reconfigurable Intelligent Surface for 6G Communications at D-Band

The Sub-THz and millimeter-wave bands have gained popularity, with the expectation that they will host the next generation of wireless communication systems. Furthermore, research on beam-steering characteristics provided by Programmable Electromagnetic Surfaces, such as Reflective Intelligent Surfaces (RISs), has garnered considerable attention as an enabling technology for 6G communications. Due to size limitations, RISs face challenges related to power consumption in the reconfigurable elements and their integration with unit cells operating at high frequencies. This paper discusses the design of a 1-bit reconfigurable unit cell at the D-band using non-volatile technology to minimize static power consumption. Simulation results show that the proposed unit cell performs well with a reflection loss of less than 1.3 dB in both reconfigurable states across a frequency band from 120 to 170 GHz. Moreover, the phase difference between the two states is maintained at $180^{\circ} \pm 20^{\circ}$, with an operational bandwidth of approximately 16 GHz. The beamforming capabilities, with steering angles from -60° to 60°, of the $12 \times 12$ RIS, utilizing the proposed unit cell, have been demonstrated in terms of controlling the main beam radiation precisely to various angles with consistent performance at frequencies of $147 \mathrm{GHz}, 152 \mathrm{GHz}$, and 152.5 GHz.