Design of Folded Waveguide Slow-Wave Structure for -Band TWT

Design of RF structure for W-band folded waveguide traveling-wave tube was accomplished using electromagnetic simulation codes CST-MWS and GdfidL. The parameters characterizing the folded waveguide structure were optimized through a detailed analysis. CST-MWS and GdfidL simulated dispersion results have been compared and found in a close agreement. The CST-particle studio and in-house developed a large-signal analysis code SUNRAY 1-D were used for a large-signal analysis. The results of the parametric analysis and large-signal analysis are presented in this paper. Dimensions have been fixed for getting a gain ~18 dB and 7% bandwidth (95-102 GHz) corresponding to a 16-kV beam line for a uniform section. A gain of nearly 24 dB was obtained by employing pitch tapering near the output section of the tube of same length. Design of folded waveguide RF structure with a simple but efficient waveguide coupler yielding a return loss better than -15 dB has been obtained in the desired band (90-105 GHz).