Design and Characterization of a D-Band Mixed-Dispersion Wideband High-Power Sheet-Beam TWT with Elliptical Staggered Double-Grid Waveguide

Conventional uniform-dispersion slow-wave structures (SWSs) for D-band sheet-beam traveling-wave tubes (TWTs) suffer from a fundamental bandwidth–efficiency trade-off that limits their performance in wideband high-power applications. To address this, this paper proposes a novel mixed-dispersion SWS based on an elliptical staggered double-grid waveguide, constructed by cascading nine units with progressively tailored dispersion characteristics. Particle-in-cell simulations with an ideal uniform sheet beam which operate at 23.0 kV, 390 mA, horizontal size of 0.70 mm × 0.16 mm demonstrate that the TWT achieves a peak output power of 779 W at 150 GHz, yielding 29.9 dB gain and 8.7% electronic efficiency, together with a 3 dB bandwidth of 24 GHz and a power–bandwidth product of 18.7 kW·GHz, with output power consistently exceeding 350 W across the entire operating band. In parallel, the electron-optical system—comprising a Pierce-type gun and a periodic permanent-magnet focusing stack with a peak field of 0.45 T and a period of 4.5 mm—is designed to satisfy the beam-parameter requirements imposed by the SWS. Electron-trajectory simulations confirm 99% beam transmission of a 23.0 kV, 394 mA sheet beam through the 100 mm long rectangular tunnel which has a horizontal size of 1.20 mm × 0.22 mm. The proposed mixed-dispersion architecture effectively breaks the bandwidth–efficiency trade-off inherent in uniform-dispersion designs, offering a viable pathway toward high-power, wideband D-band TWTs for next-generation terahertz communication and sensing systems.