A Study on Generating E-band Vortex Electromagnetic Waves with a Metasurface and Traveling-wave Tube

Statistical-state vortex electromagnetic waves exhibit divergent characteristics, making efficient long-distance propagation challenging. Traveling-wave tubes (TWT), as high-power devices, can address this issue of long-range transmission. This paper presents a study on generating high-power, statistical-state E-band vortex electromagnetic waves with topological charge l=+1 using a traveling-wave tube combined with a metasurface. A radiating system comprising a "traveling-wave tube + horn antenna + metasurface" is proposed. The horn antenna transforms the TE10 mode electromagnetic wave output from the traveling-wave tube into a plane wave, which is subsequently converted into a vortex electromagnetic wave by the metasurface. Via simulation, a horn antenna that converts the TE10 mode into a plane wave and a metasurface that transforms plane waves within the 71 GHz~76 GHz frequency band into vortex electromagnetic waves with topological charge l=+1 are designed. Simulation results validate the feasibility of the proposed method, demonstrating the near-field distribution of the vortex electromagnetic wave with l=+1 and achieving a mode purity of 97%.