Research On Lossy Dielectric-Loaded Circuits Of 220GHz Gyro-TWTs

With the rapid development of advanced radar,electronic countermeasures,highspeed communications,medical imaging and other technologies,the applications of electromagnetic waves in the submillimeter wave and terahertz region have attracted much attention in the domestic and foreign information technology communities.It is necessary to improve the properties such as the operating frequency,bandwidth,efficiency etc.for the radiation sourses of these applications.The electron beam in gyroTWTs interacts with the waveguide mode through azimuthal bunching in the phase space and transfers its transverse kinetic energy to the electromagnetic(EM)wave mode,and the operation frequency and power capacity can be improved with the low-order overmode circuits.Therefore,the gyro-TWTs,a member in vacuum electronic device family,can be applied as the high power submilimiter wave sources.The functions of dispersion relation and attenuation characteristics with the dielectric-loaded materials of the 220 GHz gyro-TWTs' circuits are analyzed by studying the eigenmode.Based on the beam-wave interaction theory,the stability and the amplified performances of the dielectric-loaded circuits are researched.The main work of this thesis is as follows:1.An automatic root-finding algorithm is designed to quickly compute the dispersion relation and field distribution of the dielectric-loaded waveguide,which is capable of solving the dispersion relation in all frequency region and recognizing the eigenmode automatically.Numerical computing programs and a graphical user interface are developed to input the parameters and output the results.The functions of dispersion relation and attenuation characteristics with the dielectric-loaded materials of the 220 GHz gyro-TWTs' circuits are analyzed,which is fundamental to design the dielectric-loaded circuits of the 220 GHz gyro-TWTs.2.The linear gain and oscillation current of 220 GHz dielectric-loaded circuits are computed based on the small-signal theory of beam-wave interaction.Combined with the automatic root-finding algorithm,the search strategy of the oscillation length,which is capable of computing the oscillation length quickly and automatically,is improved based on the orginal program.3.The dielectric-loaded circuit of the 220 GHz gyro-TWTs is designed based on the above theoretical results.The influences of the dielectric-loaded material properties on the stability of the circuits are analyzed through the particle-in-cell simulation.The dielectric parameters are optimized to ensure the stability of the circuits.Combined with the dispersion relation,the stability and the amplified performances of the dielectricloaded circuits are researched under different magnetic feld.we chose the relative dielectric constant is 6,the tangent value of loss Angle is 0.4,the thickness of the medium is 0.25 mm and the working magnetic field is 7.73 T,the saturation gain and the maximum output power of the circuit reaches the maximum 65 dB and 65 k W at 215 GHz.The 3dB bandwidth is 18 GHz.Finally,a gyro-TWTs' circuit with high-stability,high-efficiency and broadband is obtained.