Wideband Transmissive Programmable Metasurface for Adaptive Millimeter-Wave Beamforming

Programmable metasurfaces provide a promising paradigm for the beamforming of electromagnetic waves in the fifth-generation (5G) and sixth-generation (6G) wireless communications with low cost and low complexity. However, most of the existing researches are focused on the sub-6 GHz spectrum, which limited the gigabits per second (Gb s⁻¹) high-speed data transmission on future wireless network. Additionally, as a step forward in the development of intelligent metasurfaces, extra peripheral devices are often required to sense environmental variations for self-adaptive modulations. Here, a wideband millimeter-wave programmable metasurface is presented for peripheral-free self-adaptive signal enhancement in 5G/6G wireless communication. The proposed transmissive programmable metasurface consists of $20\times 20$ meta-atoms, exhibiting efficient transmission ($\le$1 dB loss) and a stable 1-bit phase difference from 23.7 to 32.1 GHz, effectively covering the desired 5G millimeter-wave frequency bands: N257, N258, and N261. By integrating the self-adaptive algorithm based on received signal intensity into the controller, the programmable metasurface can self-adaptively establish an optimal or acceptable channel according to the predefined threshold values. To evaluate the performance of the prototype, an experiment on wavefront modulation was first conducted in a microwave chamber, verifying the wideband beamforming performance of the programmable metasurface. Moreover, self-adaptive signal enhancement and millimeter-wave wireless communication experiments were conducted in indoor environments, showing a maximum signal enhancement of 21.4 dB and a significant improvement in constellation. The proposed self-adaptive wideband programmable metasurface demonstrates high potential for application in 5G/6G millimeter-wave wireless networks.