Design of a Pillbox Window for 340 GHz Traveling Wave Tubes

In this paper, the design of a 340 GHz pillbox window is presented. The pillbox window is chosen as the input/output window structure, because of its simple structure, good welding technology, wide frequency band, and high power capacity, which has been widely used in various types of vacuum electron devices. The material of the output window is chosen as the sapphire with features of high mechanical strength, relatively low dielectric constant, and nontoxicity. The initial parameters of the window are determined by equivalent theories, and then the output window is simulated and optimized by CST-MWS (Microwave Studio). Simulation results show that the designed pillbox window has obtained a reflection coefficient
$S_{11}$
of
$< -20\mathrm{d}\mathrm{B}$
and transmission coefficient
$S_{21}$
of
$> -0.06\mathrm{d}\mathrm{B}$
within the frequency range from 328 to 361 GHz. Such a performance is competitive to be used in a 340 GHz sheet beam traveling wave tube.