Study of an Ultra-Wideband Sine-Shape Staggered Waveguide for a Terahertz Band Sheet Beam TWT

A novel slow wave structure (SWS) featuring an innovative sine-shape staggered waveguide (SSW) and dual-mode operation has been developed for ultra-wideband sheet beam travelling wave tubes. In contrast to the double-staggered grating SWS, the SSW SWS is equivalent to reducing the grating height, enabling the broadening of the operational bandwidth while maintaining interaction impedance characteristics. Numerical simulations demonstrate exceptional broadband characteristics with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{{11}}$ </tex-math></inline-formula> below -15.3 dB and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{{21}}$ </tex-math></inline-formula> exceeding -8.5 dB across 237-324 GHz (87 GHz), achieving 31.0% fractional bandwidth. Cold-test results are consistent with the simulation results having considered fabrication tolerances, electromagnetic leakage, and surface roughness effects. PIC simulations predict good performance, achieving 65.0 W output power over a 76 GHz bandwidth (236-312 GHz, 27.8% fractional bandwidth), with a peak output power of 253.0 W at 250 GHz.