Design of a Pseudoperiodic Slow Wave Structure for a 6-kW-Level Broadband Helix Traveling-Wave Tube Amplifier

In this article, a potentially pseudoperiodic slow wave structure (SWS) for a broadband, high-power, helix traveling-wave tube (TWT) is studied. The structure considered here suppresses the back-wave oscillations caused by a large working current. These oscillations do not have conventional uniform pitch distributions in the radial dimension; rather, the two configurations studied in this article are a uniform pitch gradient and a conical helix. Through a reasonable design and a large number of calculations, the entire tube consists of four tapered, pitch-varying SWSs. In addition, to achieve an 8-18-GHz broadband, high-power output, a double-ridged waveguide window output coupler is designed, fabricated, and tested. The 3-D electromagnetic simulation software CST STUDIO SUITE is used to verify the performance of the tube. The simulation results show that the potentially pseudoperiodic SWS can adequately suppress the backward-wave oscillations, and the tube is capable of achieving an output power of over 6 kW, even with a very wide bandwidth of 8-18 GHz. Additionally, the electronic efficiency varies from 21.5% to 25.8%. The maximum output power is 7.45 kW, corresponding to an electronic efficiency of 25.8% at 14 GHz.