Research On Novel Integrated Multi-Beam Terahertz Traveling Wave Tubes

Terahertz wave(0.1-10THz)located between microwave and infrared wave is in the transition region from electronics to photonics.It is characterized by strong penetration,low quantum energy,non-damage,and so on.Therefore,it is widely applied in ultra-highspeed communications,ultra-high-resolution radar,electronic countermeasures,biomedicine,and modern agriculture.Terahertz wave is now recognized as an important cornerstone to enhance national security capability and an important foundation of a new generation of information industry.The generation,transmission and detection technology of terahertz wave are the main subject of terahertz research.Among them,the generation of high-power terahertz source is the key issue to the application of terahertz technology.Traveling wave tube(TWT)with high power and wide bandwidth is the most potential terahertz source in vacuum electronic devices.In terahertz band,it is difficult to realize the high current density electron optical system due to the small size of the structure and the difficulty of processing.Due to the small size of slow wave structure,it is difficult to process the various components of TWT in the terahertz band,especially the high current density electron optical system.At the same time,the decrease of electron beam channel limits the interaction current and transmission distance.Those factors limit the output power,gain,efficiency,and other performance of TWT.Focusing on the generation of terahertz vacuum electron source,this dissertation has researched novel terahertz slow wave structure(SWS)and beam wave interaction mechanism.The main work and innovations are as follows:1.A novel spindle waveguide SWS suitable for sheet beam is proposed.Compared with the traditional folded waveguide,the bandwidth and coupling impedance of the spindle waveguide SWS are improved.A TWT based on spindle waveguide SWS is designed.The maximum output power is 12.3W at 340 GHz,the gain is 30.9d B,and the electronic efficiency is 2.16%.The 3d B bandwidth is greater than 45 GHz and the gain within the bandwidth larger than 28 d B.The main performance is better than the reported340 GHz TWT whit other high-frequency structures.2.The multi-beam integrated corrugated waveguide terahertz TWT is studied.The corrugated waveguide SWS is deeply studied from theory,simulation and experiment to explore the performance of the distributed multi-beam integrated TWT.The designed Kaband three-beam integrated corrugated waveguide TWT has a maximum output power of132.8W,an electronic efficiency of 5.12%,and a gain of 41.2d B within the bandwidth of32-36 GHz.The electronic efficiency and gain are respectively greater than 1.2% and25 d B of single-beam double corrugated waveguide TWT.With an input power of 20 m W at 230 GHz,the designed G-band three-beam integrated corrugated waveguide TWT achieves an output power of 13 W,a gain of 28.1d B,an electronic efficiency of 3.7%.The electronic efficiency in the 3d B bandwidth is greater than 3%,and the gain is greater than25 d B.The results show that the multi-beam integrated corrugated waveguide TWT can significantly improve the output power,electronic efficiency and gain.It also can effectively shorten the interaction length,which is conducive to the miniaturization and integration of the device.Finally,the fabrication and transmission experiment of of the Ka-band three-beam integrated corrugated waveguide high-frequency system was carried out.In the 32-39 GHz bandwidth,the cold test S11 is less than-15 d B,which meets application requirements.The experiment explored the transmission characteristics of the multi-beam integrated corrugated high-frequency system and laid the foundation for the subsequent fabrication of TWT.3.A novel beam-wave interaction mechanism based on a feedback circuit is proposed.By rationally designing the high-frequency structure and electron beam parameters,two beams with different velocity interact with the forward wave and the backward wave respectively.The forward wave and the backward wave promote each other during the beam-wave interaction,forming a beneficial positive feedback circuit,and realize the stable amplification of the forward and the backward wave.Based on this novel mechanism,a 140 GHz dual-channel folded waveguide forward-backward wave feedback amplifier was designed and an output power of about 2W for both the forward wave and the backward wave was achieved.Compared with the single-beam TWT,the saturated input power of the forward-backward wave feedback amplifier is reduced to 25 percent,and the gain is increased by 12.4d B.Compared with the traditional BWO,the starting current of the feedback circuit is reduced by 44.4%.Therefore,the forwardbackward wave feedback amplifier can achieve stable output power with lower input power and lower electron beam current.4.An electron optical system with a cathode-anode hybrid structure is designed for the feedback circuit.One electron beam has a voltage of 15700 V and a current of 0.012 A.The voltage of the other electron beam is 5700 V and the current is 0.025 A.The voltage difference between the two beams is 10000 V and the axis distance is 0.433 mm.The whole optics system shares a set of focusing magnetic system and collector.The stable transmission in 80 mm long distance is realized,which further verifies the feasibility of the forward-backward wave feedback amplifier.Finally,the cathode-anode hybrid structure was fabricated and the heater side loading test was explored.The research on the high-frequency structure and beam-wave interaction mechanism of terahertz TWT carried out in the dissertation provides a new solution for the design and realization of high-power terahertz sources and lays the foundation for future terahertz applications.