Gain Calculation And Stability Study Of The Tapered Interaction Circuit Of Gyro-TWTs

The gyro-traveling-wave tube(gyro-TWT)is an important high-power millimeterwave coherent radiation source.It has the characteristics of wide bandwidth,high power and high gain,and has import application value and broad application prospects in various fields such as communications,remote sensing,radars,electronic countermeasures and medical imaging systems.As the key component of the gyro-TWT,the circuit stability directly affects its amplification performance,and even leading to operation failure in serious cases.The stability of gyro-TWTs is closely related to the circuit gain of the operating mode and parasitic modes.The lower gain of the lower-order backward oscillation mode and operating mode near the oscillation frequency is,the higher oscillation threshold of the absolute instability could be achieved.Moreover,the flatter gain response of the operating mode is,the better flatness of the device could be achieved over the operating bandwidth.In this thesis,the oscillation characteristics of the operating mode and parasitic mode of the cylindrical waveguide circuit are analyzed.Then,the gain calculation method is studied,which is suitable for circuits with arbitrary circuit profile.The stability of circuit can be judged by the frequency response of small signal gain.The main work is as follows:1.Combined with the theoretical analysis of the dispersion curve,the oscillation characteristics of the Ku-band gyro-TWT are analyzed with different parameters through the 3D particle-in-cell simulation(PIC)codes on the basic of the small-signal theory.2.Our preliminary codes of calculating the oscillation current and the oscillation length have been improved.The oscillation threshold with the operating magnetic field,beam current and pitch ratio is calculated and the contours are plotted for a G-band gyroTWT,which are verified by CST PIC codes.It is found that a tapered interaction circuit with a small angle can effectively suppress oscillation threshold.3.Based on our preliminary codes for uniform circuits and magnetic fields,this thesis uses the idea of infinitesimal to equate the curved profile as a superposition of a series of short units.The total gain response can be obtained by the linear superposition of the gain of each unit,and successfully verified by large-signal codes.In this way,the stability of gyro-TWT is judged by calculating the gain for both the uniform and nonuniform circuits.Finally,a G-band gyro-TWT with broadband and high-efficiency amplification performance is designed,which has high stability thanks to the used of gradually-tapered circuit.