Simulation of Rectangular Helix Slow-Wave Structure for 140 GHz Traveling-Wave Tube

The rectangular helix has been proposed to develop a low-voltage, wide-band, and high-power millimeter-wave traveling-wave tube (TWT). This structure, which is evolved from the original circular helix slow-wave structure, is a kind of planar structure, which is suitable for the microfabrication technology. The high-frequency characteristics of the rectangular helix structure, including dispersion properties, interaction impedances, and reflection characteristics are investigated. The interaction between the sheet electron beam and the slow wave in the structure is also obtained by utilizing the particle-in-cell code in CST Particle Studio. A circuit sever is set into the rectangular helix to reduce the backward wave oscillation. Our calculations indicate that, at beam parameters of 9.95 kV and 40 mA, the averaged output power and the electron efficiency can reach 46 W and 11.5% at 140 GHz, respectively, and a transient 3-dB bandwidth of 6 GHz (ranging from 137 to 143 GHz).