Investigation of a 220 GHz Traveling-Wave Tube Based upon a Flat-Roofed Sine Waveguide with a Coupling Structure

This paper presents the design and investigation of a two-stage flat-roofed sine waveguide (SWG) traveling-wave tube (TWT) incorporating a novel coupling structure. Initially, the slow-wave structure (SWS) of a 220 GHz flat-roofed SWG was optimized, and the output performance of the corresponding TWT was thoroughly analyzed. Subsequently, a specialized coupling structure was designed and fabricated, with the experimental results demonstrating an excellent agreement with the simulation predictions. The coupling structure exhibits low reflection and is easily manufacturable, making it highly suitable for energy coupling in two-stage TWTs. Finally, a two-stage TWT, integrating both the optimized flat-roofed SWG structure and the coupling structure, was developed and characterized. Under operating conditions of a 20.8 kV beam voltage, 150 mA current, and 150 mW input power, the proposed TWT achieved remarkable performance metrics: a maximum output power of 160 W within the frequency range 210–230 GHz and a 3 dB bandwidth exceeding 20 GHz. This research provides a valuable reference solution for the realization of high-power, broadband terahertz radiation sources, contributing significantly to the advancement of terahertz vacuum electronic devices.