Study On The Millimeter-wave Novel Folded Waveguide Traveling Wave Tube

Millimeter-wave Traveling Wave Tube (TWT), working in the frequency range between the microwave and infrared, has advatanges of wide absolute-band, narrow wave-paket, ability of all-weather working and large output power. It is widely used in radar, communications, remote sensing, electronic countermeasures and plasma diagnostics. Therefore, it has importantly realistic significance for the study on the new type mm-wave traveling-wave amplifiers. In this dissertation, based on the investigation of a Ka band folded-waveguide traveling-wave tube (FWTWT), we have made detailed theoretical, particle-in-cell (PIC) simulation and experimental study on several new types of FWTWT. Some important and valuable results which bring forth some new ideas are accomplished and listed as the followings:1. The dimensions of slow-wave structure (SWS), attenuator and coupling structures are designed, and the energy exchange between the electronic beam and the microwave are investigated in a 3D nonlinear interaction model. A FWTWT is assembled for experiment test, in which a 95W saturated power is observed, and the output power and large signal gain of experiment test agree with the former PIC simulation results. The investigation reveals that: as one of the all-metal SWS, the folded waveguide slow-wave structure (FWSWS) could realize the beam-wave synchronization in a relatively wide frequency band and have large power capacity, which implies the FWTWT is one of strongest candidates for a wideband high power mm-wave radiation sources. These results obtain in this work set a solid theoretical and experimental base for the following study.2. In order to improve the bandwidth of FWTWT, the E-bend folded double-ridged waveguide TWT is investigated. The slow-wave characteristics including dispersion characteristics, normalized phase velocity and interaction impedance of this structure are investigated. The linear theory of beam-wave interaction is developed, and a 3D simulation model is built and the nonlinear interaction is investigated by PIC simulation. It is shown from the results that: the folded double-ridged waveguide TWT has wider bandwidth than the convetinonal FWTWT; the 3dB bandwidth of TWT is raised up 75%. These obtained results are useful for designing wide band and large power TWT.3. A Ka band ridge-loaded folded waveguide TWT, formed by loading ridges on the straight portions of FWSWS, is developed and investigated. The high frequency characteristics of this novel structure and the property of its linear gain are theoretical analyzed. The beam-wave large signal interaction is simulated and investigated by MAGIC 3D. An experimental test is also carried out to study the characteristics of this novel TWT. It is found in these works that: with the increase ridge dimensions, the interaction impedance and small signal gain is raised, while the dispersion of this structure is enhanced and the 3dB gain bandwidth is narrowed. The chose of the ridge dimensions should be made properly as a compromise of the dispersion characteristic and the interaction impedance. In the experiment test, the saturated output power is apparently raised by ridge-loading, which is more than 100W in the range of 33-37GHz. Eespcially, a 154W saturated power is obseverd at 34.5GHz, which is 59W larger than the test results of FWTWT.4. An investigation of groove-loaded FWSWS is carried out to improve the performance of FWTWT. Two different structures are proposed in this part: single groove-loaded structure and double-groove loaded structure. The expressions for the dispersion and the interaction impedance of these novel structures are obtained by using matching conditions of the RF fields. Numerical calculation for different combinations of the groove width and depth is carried out to study the influence of groove loading on the properties of SWS. The linear theory of groove loaded folded-waveguide TWT is developed and calculated for analyzing the effect of groove dimensions on the property of small signal gain. The enhancing of beam-wave interaction is approved by PIC simulation. The investigation results indicate that: the interaction impedance and the small signal gain are raised by loading grooves in the FWSWS, while the dispersion is enhanced and the bandwidth is reduced. Compared with the conventional FWTWT, the double groove-loaded FWTWT could obtain higher saturated output power and gain in a shorter interaction length. The maximum of output power and gain of this novel TWT is 53.6% and 21.4% higher than those of FWTWT. With the additional advantage of high power-handling capability and robust structure, the groove-loaded FWTWT holds promise for application in millimeter TWTs.