Research On Traveling Wave Devices For Terahertz Coupled Slow Wave Circuits

The terahertz band which locates between the microwave and infrared bands is still the least utilized electromagnetic spectrum.At present,terahertz technology has become a research hotspot and attracted increasing attention because of the optimistic future of the Terahertz research.For some applications,it is necessary to implement a terahertz source with higher output power and lower cost.Unfortunately,there is few achievements in research due to the limitations of research methods and machining technology,which leads to the bottleneck of the terahertz applications.In this paper,the terahertz traveling wave devices are focused,and the coupled slow-wave structure shunting technology is the main topic.Much effort is focused on the research of output power and efficiency contributed by the slow-wave structure shunting technology conjugated with two different types of slow-wave structures.The main work and contributions of this thesis are the following:(1)The efficiency of the traveling wave devices with coupled shunt slow-wave circuits is discussed.By discussing the parameters which affect the space charge field and the relationship between the total space charge field of the one-electron beam and the space charge field after shunted,the relationship of the total efficiency of the devices with and without the shunt slow wave circuit is figured out.At the same time,based on the above result,the modes of the shunt slow-wave circuits and the equivalent Pierce impedance are discussed.This work provides a theoretical guidance for future terahertz traveling wave device research.(2)A 670GHz-band grid-loaded rectangular waveguide backward wave oscillator(BWO)with coupled shunt slow-wave circuits is proposed.The high-frequency characteristics of the grid-loaded rectangular waveguide slow-wave structures with one or more slow-wave circuits shunt are intensively analyzed.The energy coupling structures of these BWOs are designed,which ensure the TWTs operating steadily.Then,three 670GHz-band grid-loaded rectangular waveguide BWOs with single,double and four slow-wave circuits shunted are constructed.The simulation results show that the output power and electron efficiency of the BWO with double slow-wave circuits shunt are 2.54 and 1.282 times than that of the single slow-wave circuit shunted BWO,respectively,and the output power and electron efficiency of four slow-wave circuit shunted BWO are 5.79 and 1.436 times than that of the BWO with a single beam.The beam-wave interaction efficiency is absolutely increased because of the growth of the number of the coupled shunt slow-wave circuit.The work in this paragraph lays the foundation for the development of broadband high-power terahertz BWOs in the future.(3)The staggered double vane traveling wave tube(TWT)with multiple coupled shunt slow-wave circuits is proposed.The variation of the dispersion characteristics of the staggered double vane SWS caused by shunting the circuit with coupling structure is discussed,and the high-frequency characteristics of staggered double vane SWS with one or more slow-wave circuits shunt are intensively analyzed.The energy coupling system that can greatly reduce the reflection coefficient for this kind of TWTs is designed,which ensures the TWT operating steadily.Then,sheet-beam staggered double vane TWTs with single,double and four slow-wave circuits shunt are constructed.The simulation results show that,compared with the output power of the single slow-wave circuit TWT,that of double slow-wave circuits shunted TWT is increased to 174%,that of four slow-wave circuits shunted TWT is increased to 255%,and they are stable in a broadband.(4)The slow-wave circuits of W-band staggered double vane TWT with double slow-wave circuits coupled shunt is fabricated.This experiment results show that the voltage standing wave ratio(VSWR)of the slow-wave circuits of double-beam staggered double vane TWT is less than 1.2,as well as the S11 and S21 below-20 dB and above-1.25 dB,respectively.The experiment results of the transmission characteristics of the slow-wave circuits verify that the compatibility between the designed energy coupled system and the slow-wave circuit,and the correctness of the simulation results.It's useful for the hot experiment in the future.