Simulation and Experimental Investigation on W-Band Back-to-Back Longitudinal Serpentine Groove Slow Wave Structures

Based on the traditional serpentine groove waveguide (SGW) slow wave structure (SWS), a novel back-to-back SGW (BTBSGW) is proposed in this article. The BTBSGW maintains the operational mode characteristics of conventional SGW while implementing dual-symmetric SGW that shares a common sheet beam, achieving two key improvements: 1) expanding the beam configuration and 2) simplifying the gun design. Through comprehensive high-frequency analysis, the dispersion characteristics, electric field distribution, coupling impedance, and transmission characteristics of the BTBSGW were investigated. Particle-in-cell (PIC) simulations were further conducted to evaluate the stability, saturation power, gain characteristics, and electronic efficiency of the BTBSGW traveling wave tube (TWT). Specifically, the BTBSGW-TWT is expected to achieve a gain exceeding 20 dB across the 86.5–92-GHz frequency band under fixed electron beam conditions (18.8 kV, 0.27 A). Peak performance occurs at 90 GHz, achieving a conversion efficiency of 5.97% and an output power of 302.06 W. To validate the design, the BTBSGW was fabricated using nano-computer numerical control (CNC) processing technology and the cold-test experiment was carried out. The experimental transmission characteristics exhibited a high degree of agreement with the simulation results. Overall, the BTBSGW-TWT demonstrates promising potential for applications in high-speed communication systems.