Design of a High-Order Mode Corrugated Slow Wave Structure With Large Beam Tunnel for Traveling Wave Tube

In the millimeter wave and terahertz band, the size of vacuum electronic devices becomes small, typically close to the wavelength, which poses a great challenge to manufacturing and assembly. High-order mode operation allows for comparatively larger circuit dimensions at the expense of mode competition. Here, we report on the development of a corrugated slow wave structure (CSWS) that is placed outside the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$</tex-math> </inline-formula>-plane of the rectangular waveguide. The likely TM<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${}_{\mathbf {{11}}}$</tex-math> </inline-formula> mode is excited in the CSWS during TE<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${}_{\mathbf {{10}}}$</tex-math> </inline-formula>-mode excitation, and a high-order hybrid operating mode is achieved. The transmission characteristics of the fundamental mode and high-order hybrid mode in a high-frequency circuit are obtained simultaneously in this <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i>-band experiment. As a result of the strong longitudinal electric field component of the hybrid mode in this CSWS, the radius of the beam tunnel can be increased by approximately 60%. Meanwhile, the mode competition can be effectively suppressed with the increase in the size of CSWS. A 1-THz traveling wave tube (TWT) operating near a phase of 505° is designed to compare with the size of the beam tunnel. The diameter of the beam tunnel can reach up to 0.1 mm. The simulation results show that the maximum output power is 1.12 W at 1028 GHz, and the −3-dB bandwidth (BW) is 7 GHz.