Design and Cold Test of Flat-Roofed Sine Waveguide Circuit for W-Band Traveling-Wave Tube

The W-band flat-roofed sine waveguide (SWG) slow wave circuit was designed and processed in this article. Considering the limitations on present practical fabrication level, sensitivity analysis was performed on the potential influencing factors for the performance of the flat-roofed SWG slow wave structure (SWS). As indicated by the calculation results, the gap between the SWSs and the side-wall strips could have a significant impact on the dispersion, interaction impedance, and the transmission of the entire slow wave circuit. Based on the theoretical analysis, two types of W-band flat-roofed SWG slow wave circuits were fabricated and tested. The side-wall strips of the two circuits are processed with/without rounded corner. The circuit without rounded corner may cause a large gap and severe reflection. In comparison, the other one with rounded corners can make the parts fit tighter, thus minimizing the potential gap. The test results demonstrate that the W-band flat-roofed SWG traveling-wave tube (TWT) possesses a voltage standing wave ratio less than 1.8, which is basically consistent with the simulation results.