Multi-frequency compact encoding metasurface for independent beam control

Encoding metasurfaces, as innovative materials that facilitate the integration of the physical and digital realms, offer engineers a more streamlined and effective approach to manipulating electromagnetic waves. In order to modulate electromagnetic waves at multiple frequencies with a single metasurface as much as possible, researchers adopt methods such as mechanical stretching and multilayer stacking to design a variety of structures. However, these works all have problems like complex structures and inconvenience in use. Therefore, it is still a challenge to design a metasurface that can flexibly modulate electromagnetic waves at multiple frequencies by using a simple structure. In this paper, we present a reflective encoding metasurface capable of independently modulating the phase at two disparate frequencies. This is achieved through the manipulation of octagonal copper rings and copper patches on the meta-atom. To enhance and achieve more precise beam control accuracy, a genetic algorithm is utilized to optimize the arrangement of low-frequency and high-frequency structures individually, which are then integrated to facilitate beam deflection at both frequencies. The simulation results demonstrate that the proposed compact dual-frequency coded metasurface effectively controls the incident electromagnetic waves at 6 GHz and 19 GHz, and realizes the beam deflection within the range of elevation angles from 0 degrees to 45 degrees and azimuth angles from 0 degrees to 360 degrees in the half-space. Measurements are performed in a microwave anechoic chamber to verify the simulations, and the measurement results are consistent with the simulations. The proposed metasurface has potential applications in compact space and multi-channel communication services due to its good beam control capability.