Time-modulated metasurfaces with both amplitude and phase control ability at carrier frequency

Although time-modulated metasurfaces (TMMS) possess flexible beam manipulation capability, they often operate at harmonic frequencies, which weakens their practicality. To solve this problem, a method enabling TMMS to achieve beam-forming at the carrier frequency is proposed and investigated. Specifically, the phase is controlled by a reconfigurable metasurface (MS), and additional time modulation (TM) amplitude excitation is introduced by utilizing an anti-phase modulation time sequence (APMTS) to achieve complete control of the reflection coefficient for each element. The working principle is elaborated in detail, and the effectiveness of the proposed method is verified by theoretical analysis. As a proof of concept, experimental validation is then carried out using a 10 × 10 1-bit TMMS prototype. The theoretical and experimental results show that the proposed method can enable the 1-bit TMMS to have the capability of controlling the amplitude and phase independently and simultaneously at the carrier frequency. Furthermore, this paper introduces, for the first time, a rigorous efficiency definition for TMMS, followed by an accurate efficiency analysis that demonstrates the proposed method achieves higher TM efficiency in beam-forming compared to conventional methods. Benefiting from the physical perspective analysis, the proposed method is clear in principle, simple in structure, and easy to implement. It may have potential applications in wireless communications, target sensing, and radar systems.