Study On Some Characteristics Of Mircostrip Meander-Line Traveling Wave Tube

The traveling wave tube（TWT）is one of the important microwave and millimeter wave sources in space communication,radar detection and military confrontations.With the rapid development of 5G,6G communication and miniaturized detection radar in recent years,miniaturized signal sources have gained wide attention.Planar microstrip meander-line TWT is an important branch of miniaturized TWT,whose slow wave structure can be fabricated in large quantities by modern microfabrication process,and the micro-fabricated slow wave structure has great consistency.Nevertheless,the planar microstrip meander-line traveling wave tube also faces inherent problems such as poor thermal conductivity,difficulty in planarization of electron optical system and dielectric charging.In this thesis,an exploratory study is started to address these problems by combining modern processing techniques.The research work and results of this thesis can be summarized as follows.（1）An efficient thermally conductive thermal pyrolytic graphite（TPG）material with more than four times the thermal conductivity of copper in the parallel deposition layer direction is investigated,and the combination with the slow-wave structure（SWS）can improve the heat dissipation performance.A microstrip meander-line SWS with TPG layer in the frequency band of 90～100GHz is designed.The loss is 10～11.5d B/cm when conducting heat along the parallel deposition layer of TPG,which is 30%higher than that by conducting heat along the vertical deposition layer;the analysis of the beam-wave interaction characteristics of the TWT shows that the average output power is 15.5W at96GHz,which is 12W lower than that without TPG;the temperature distribution of the SWS under the two thermal conduction methods of TPG is calculated,and the thermal characteristics of the SWS can be improved by about 31.3%when the parallel deposition layer direction is used for direction of heat transfer.（2）In order to improve the heat dissipation performance of the substrate of the microstrip meander-line SWS,a boron nitride（BN）ceramic with high thermal conductivity is used as the substrate material of the SWS,and a microstrip meander-line TWT based on the BN substrate is designed.The high-frequency structure dimensions of the SWS on BN substrate are obtained through simulation;the beam-wave interaction analysis of the microstrip meander-line TWT based on BN substrate is performed,and the average output power of the TWT can reach 24.97W at 96GHz,corresponding to a gain of 23.97d B and a 3d B-bandwidth of 5GHz.Microstrip meander-line SWS on BN substrate was microfabricated based on existing process conditions,and the transmission characteristics was tested,S₂₁>-6.5d B,S₁₁<-10d B in 90～98GHz,the measured loss per unit length is 6.8～9.2d B/cm.（3）A planar depressed collector was designed,which not only has high collecting efficiency,but also can be integrated with the SWS and easy to integrate.When the secondary electron emission is not considered,the collector efficiency can reach 93.31%,and the full-band collector efficiency can reach more than 87%;when the secondary electron emission is considered,the maximum collector efficiency can reach 93.22%.（4）Dielectric charging in planar microstrip meander-line SWSs was studied.By using computer simulation methods,it is confirmed that plating semiconductor film on the dielectric surface can reduce the dielectric charging;the film conductivity test experiment of the plated semiconductor thin film slow wave structure is carried out,and the test model is designed.The conductivity of this film is proved by monitoring the current flowing through the film.