Optimized Design of <i>W</i> -Band High-Power Folded-Waveguide Traveling-Wave Tube

This article presents a series of research studies on performance enhancement for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i>-band folded waveguide (FWG) traveling-wave tubes (TWTs), aiming to meet the increasing demand for high-power and high-efficiency millimeter-wave sources. In the first device (TWT1), a FWG slow wave circuit in which the straight waveguide height is smaller than the electron beam tunnel diameter is employed. This design improves dispersion flatness and coupling impedance, thereby enabling stable operation with an output power exceeding 116 W. To further enhance the output power, phase velocity tapering (PVT) technology—combining both positive and negative tapering—is introduced in the subsequent device, TWT2. Although the simulated output power exceeds 200 W, hot test results revealed self-excited oscillations caused by excessive gain in the input section. To suppress these oscillations while maintaining an output power above 200W, the slow wave circuit is designed with a three-section structure. Building on insights gained from the two earlier prototypes, a third TWT (TWT3) is developed, achieving stable operation without oscillation and improved output performance. Experimental results demonstrate that TWT3 delivers an output power exceeding 200 W, a gain greater than 32 dB, and an electronic efficiency of more than 5.5% across the 92–98 GHz frequency range. The output spectrum remains clean, with no signs of oscillation observed. These results provide a valuable design reference for the development of high-performance <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i>-band vacuum electronic devices.