Theoretical And Experimental Study On Folded Waveguide Traveling Wave Tube

Traveling wave tubes (TWTs) become the most important vacuum electron devices(VEDs)， which are widely used in millimeter radar, communication, remote sensing,spectroscopy, electronic countermeasure application. The slow wave structure (SWS) isthe core part of the traveling wave tube for generating or amplifying the microwave.Therefore, the performance of the SWS is closely related to the technical level oftraveling wave tube. The SWS gradually becomes one of the reaserch hot and difficultpoints. Meanwhile, the process of beam-wave interaction is the most important part ofthe mechanism and kernel theory for TWT that would impact on the performancebecause of the modulation of the electron beam and the beam-wave energy exchange.So, it is significant for the study on the novel SWS and calculation the nonlinearbeam-wave interaction process.Compared to the conventional Helix-TWTs and coupled cavity (CC) TWT, the foldedwave-guide (FWG) TWT can provide larger bandwidth and higher average powerhandling capability. In principle, FWGTWT circuits are also easier to fabricate thanCCTWT circuits. This feature has motivated an investigation of the FWGTWT as acompact coherent source in the submillimeter or terahertz spectrum.In this dissertation, the high frequency characteristics of the traditional foldedwave-guide (FWG) TWT and different kind of ridge-loaded SWS have been analyzedby the equivalent circuit method based on the transmission cascadeing network. Thetheoretical results agree well with those obtained by the3-D electromagnetichigh-frequency simulation software (HFSS). In order to improve the nonlinearinteraction model, disk-loaded waveguide play an important role in calculation thespace charge field of the FWGSWS. Finally, ridge loaded FWGTWT which works atW-band is assembled and the relative experimental test results are reported.Severalimportant and valuable results in this doctoral dissertation are listed as follows:1、The equivalent circuit theory of the conventional FWTWT has been improved. It isdifficult to analyze the high frequency characteristics according to the field-matchingmethod because of the complicated boundary conditions of this kind of the structure.We have improved the equivalent circuit theory of FWTWT by considering the bendingand the discontinuity of the path of the electromagnetic wave propagation. It can be included that the HFSS simulation datas agree with the numerical calculation datas fromthe equivalent theory, which can support our theory.2、The equivalent circuit models of the signal ridge-loaded FWGSWS are presentedinnovatively, including the E-plane ridge-loaded FWGSWS and the H-planeridge-loaded FWGSWS. We have analyzed the high frequency characteristics of theFWGSWS with the help of the equivalent circuit theory and the HFSS. It can beincluded that the HFSS simulation datas agree with the numerical calculation datas fromthe equivalent theory, which can support our theory.3、A novel double ridge-loaded FWGSWS with is proposed innovatively. Comparedto the other kind of the FWGSWS, this structure possesses higher power capacity,electronic efficiency and larger transverse dimensions. The equivalent circuit model ofthis novel SWS has been established based on the previous research results aboutconventional FWGTWT and signal ridge-loaded FWGTWT. The results show that theHFSS simulation datas agree with the numerical calculation datas from the equivalenttheory of the novel SWS. The interaction circuit for220GHz TWT is designed by usingthis structure. The particle-in-cell (PIC) simulation results reveal that the220GHzdouble ridge-loaded TWT can provide higher power in a broad band.4、A novel tapered H-plane ridge-loaded FWGSWS is proposed. The design of theW-band high-power TWT is completed by using this structure. The particle-in-cell (PIC)simulation results reveal that the W-band tapered H-plane ridge-loaded TWT canprovide higher power in a broad band. This study lays a solid foundation for developinghigh efficiency and high power sub-millimeter wave amplifiers.5、A novel double ridge-loaded FWGSWS is proposed. The design of the140GHzhigh-power TWT is completed by using this structure. The particle-in-cell (PIC)simulation results reveal that the140GHz double ridge-loaded TWT can provide higherpower in a broad band. This study lays a solid foundation for developing high efficiencyand high power sub-millimeter wave amplifiers.6、The software analysis platform of these FWGTWT called FWTWT SUITE hasbeen set up by combining the numerical calculation of the high frequency characteristicsand the1-D nonlinear theory of beam-wave interaction of the FWTWT. All the codesare written in MATLAB programming language. Moreover, according to the results ofthe parameter optimization by the FWTWT SUITE, an E-plane ridge loaded FWGTWTwhich works at W-band has been assembled and the relative experimental test are carried out to study the performance. The experimental results and the calculationresults of FWTWT SUITE have the same trend in the operating frequency band. Itmeans that the software analysis platform of the FWGTWT would bring manyadvantages for rapid parametric studies in the early TWT design.7、Combining the traditional nonlinear beam-wave interaction theory with theequivalent circuit method, the improved model of the nonlinear beam-wave interactionabout the FWGTWT has been proposed in the dissertation. In order to analize the spacecharge field of the FWGTWT, the disk-loaded waveguide should be a suitableequivalentstructure of the FWGTWT for the calculation of the space charge field based on thesimulation results of the Maxwell software.