Investigation Of The Azimuthally Periodic Circular Waveguide Traveling Wave Tube

With the development of modern science technology, the investigation on highpower miniature radiation sources became an important research direction of electricvacuum device. The traveling-wave tube (TWT) is one of the most important electrondevices due to its outstanding combined performance in bandwidth, power capacity,reliability and so on. In this dissertation, how to improve the output power and expandthe bandwidth of the millimeter-wave TWT is studied, therefore, dielectric-linedazimuthally periodic circular waveguide (DLAP-CW), open-styled dielectric-linedazimuthally periodic circular waveguide (open-styled DLAP-CW) and helix-loadedazimuthally periodic circular waveguide (HLAP-CW) are proposed, which can operatein millimeter-wave and short millimeter-wave TWT with the characteristics of simplestructure and easy processing. In this dissertation, we have made numerical theoreticalanalysis, computer simulation and experimental study on new slow-wave structures.Several important and valuable results which bring forth some new ideas areaccomplished and listed as the followings:1. In order to improve the interaction efficiency and gain, a dielectric-linedazimuthally periodic circular waveguide is proposed which is a modified form of aconventional dielectric-lined circular waveguide. The slow-wave characteristics andthe linear theory of beam-wave interaction are studied by numerical method. The effectof the structure parameters on the dispersion characteristics is obtained. The results areshown that the interaction impedance and the operating frequency of the DLAP-CWare both much higher than those of the DL-CW when the DL-CW and the DLAP-CWhave the same dimensions; when the dispersion characteristics of the two structures aresame, the interaction impedance of the DLAP-CW has increased by a factor of4.3onaverage. The particle-in-cell simulation results for Ka-band DLAP-CW TWT show thatmore than1200W output power can be produced at the central frequency of30GHzbecause of the metal rods, which increases44.8%than the output power of DL-CWTWT.2. In order to suppress mode competition, improve the interaction efficiency and the stability, an open-styled dielectric-lined azimuthally periodic circular waveguide isput forward. Equations for the slow-wave characteristics including phase velocity andinteraction impedance are derived, and the linear gain characteristics of the open-styledDLAP-CW are obtained. Furthermore, the process of the nonlinear beam-waveinteraction in open-styled DLAP-CW TWT is simulated by CST PIC-Solver. Theinvestigation reveals that: the transmission coefficient of the competition modes are allless than-12dB except the operation mode in open-styled structure. And the outputpower and the interaction gain of the open-styled DLAP-CW TWT are effectivelyimproved. Compared with a DLAP-CW TWT, the saturated power and the interactiongain of the open-styled DLAP-CW TWT are improved28.3%and3.7%.3. In order to solve the problems of output power and focusing of theconventional helix TWT in short millimeter-wave, a helix-loaded azimuthally periodiccircular waveguide is proposed. In the novel structure, N-helixes interact with oneelectron beam having larger current. The effects of the SWS parameters on the RFcharacteristics are discussed using Ansoft HFSS. In addition, analytical solutions forthe dispersion characteristics and interaction impedance of the HLAP-CW are derived,which lays the theoretical basis for subsequent design. Furthermore, a140GHz theHLAP-CW TWT is designed, and the beam-wave interaction characteristics areobtained by Particle-in-cell simulation. When the operation voltage is3758V, thecurrent is0.25A, and the input power is50mW, the output power, the maximal gainand the electronic efficiency of this TWT is55W,25.98dB and8.43%, respectively.Therefore, it has potential for application in millimeter wave and even Terahertzdevices.4. In order to verify the accuracy of the theory of RF characteristics and thereliability of the progress of computer simulation in this dissertation, we design ahelix-loaded azimuthally periodic circular waveguide, and the slow-wave properties ofHLAP-CW are investigated by experimental method. The experimental results are ingood agreement with the simulation data, which prove the correctness of the theoryand the simulation.