Active Gain-Controlled Beam-Steering Transmissive Surface

Engineered electromagnetic surfaces enable enhancing the strength of a signal in the desired direction(s) using anomalous reflection/transmission. However, to boost the gain of the conventional surfaces, the common solution is to increase its aperture size where this method limits the gain performance for limited space in scenarios for large-distance communication. This paper proposes a gain-controlled beam-steering polarization-engineered transmissive surface to tackle this challenge. To implement such a functionality, a transmissive unit cell properly integrated with transistors and phase shifters is introduced with the ability of simultaneous manipulation of phase, amplitude (reduction and amplification), and polarization. Then, a supercell including the array of unit cells with desired linear phase gradient is designed and analyzed using Floquet approach to tilt the transmitted beam. Finally, to verify the proposed idea, a surface including $12\times 12$ unit cells is designed, fabricated and verified. It is demonstrated that a maximum gain of 25 dB compared to air aperture and 11 dB compared to the passive one are achieved by assuming a constant size at 5 GHz. Based on this gain improvement, the active surface’s aperture efficiency is 12.58 times greater than that of the passive surface. Moreover, the surface gain can be reconfigured by the amplification level of the transistors, providing efficient dynamic way for changing the gain instead of the static resizing of aperture.