S-band Plasma Coupled Cavity Traveling Wave Tube Coupling Structure Of The Theoretical Design And Testing

Design and adjustment for coupled structure is an important step to develop the coupled-cavity traveling-wave tube. Although the high-frequency system determines the characteristics of the fundamental bandwidth of tube, but the frequency response of coupled structure also affects the overall bandwidth.Coupled structure as a key component in coupled-cavity traveling-wave tube, which makes high-frequency power can be no loss or the loss as small as possible (including resistive loss and reflection loss) from the outside transmission lines to the slow-wave structure or from the slow-wave structure to the outside transmission lines. There are some appearances such as electromagnetic conversion, impedance matching between the two different performances transmission lines.This paper is based on the theory of long-line equivalent circuits. It changes the Hughes coupled-cavity traveling-wave tube into the four-port equivalent networks correspondingly. It uses the voltage and current of equivalent circuits to replace the propagation characteristics of slow-wave system. It uses the models of equivalent circuit to analyze the inherent resonant frequency of coupled-cavity and the resonant frequency of slot. The equivalent line method is a similar analysis, it can be avoided the calculation of complex boundary conditions.This paper uses three-dimensional high-frequency electromagnetic simulation software CST Microwave studio to analyze and calculate the broadband match performance of three transition structures which used in S-band coupled-cavity traveling-wave tubes. The transition structures include linear structure, surface structure and the step structure. At last, it calculates the VSWR of respective structures. Comparison of the three respective characteristics and focusing on the third-order structure, this paper optimize the design to meet the VSWR requirements. However, the length of third-order structure is the shortest among the three structures.Adjusting of the simulation size of the third-order structure, it can meet the requirements both in the performance and the precision of manufacture. Two transitions were produced, and the measurable moth was designed on the test platform. The test results can be directly used in the design of tube.