Research On Terahertz Folded Waveguide Based On Thin Dielectric Layer Slow-wave Structure

Compared with other frequency bands,terahertz wave(THz)band has unique characterization.Therefore,it has significant value in communication science,biology,medicine,astronomy,environmental science,safety detection and other fields.The lack of room-temperature terahertz source which has the performance of high-power,low-cost and portable is the most major factor that limits of THz applications.Traveling wave tube(TWT)is a vacuum electronic device.It has advantages such as high frequency,high gain and small size.It is feasible to combine TWT with existing THz source,which has characteristics such as low cost,portable and weak output power.At present,the major slow-wave structure(SWS)of THz TWT is folded waveguide(FWG)structure,which has advantages such as large size,wide bandwidth,large power capacity,has been broadly investigated.However,the phase velocity of FWG SWS is relative high.In order to match the speed of electron beam and electromagnetic wave,high boost is needed in FWG TWT,which limits the practical use of FWG SWS in THz application.In this thesis,a novel structure named folded waveguide based on thin dielectric(FWG-TD)is proposed to reduce the phase velocity of FWG SWS,which is based on the phenomenon that the transverse electric field will propagate in air and dielectric material at FWG-TD.The mechanism of the novel slow wave structure is expounded and the feasible structure is proposed.The theory and simulation results show that due to the addition of thin dielectric,the main part of transverse mode in vacuum while the other part propagates in dielectric as attenuation mode,which leads to lower phase velocity compare with conventional FWG SWS.In order to ensure the transmission performance between FWG-TD and metal waveguide,the input and output coupler structure between FWG-TD and rectangular waveguide is designed.The simulation result shows that the coupler has good transmission characteristics.Finally,particle-in-cell(PIC)simulation of FWG-TD at 850 GHz is carried out in this thesis using the optimized parameters obtained by cold-test simulation.The PIC simulation results show that at 850 GHz,when the input voltage is 50 mV,in other words,the input power is 1.25 mW,output power of FWG-TD is saturated and the power is 605 mW and gain is 26.85 dB,which is sufficient for general applications.Therefore,FWG-TD greatly expanding the feasibility of THz applications.