Research On Ka-band Interdigital Crossed-Field Amplifier

As a vacuum electronic device developed so far,Crossed field amplifier has very distinct characteristics,including the main advantages of low operating voltage,phase stability,high efficiency,high power,small volume,etc.,low gain and signal to noise ratio compared with traveling wave tube and klystron weak board.Widely used in phased array radar and other fields,it is a high power microwave source that can work with cold cathode.In this thesis,a Ka band interdigital Crossed field amplifier is designed.Through theoretical research and simulation design,the operating frequency and gain are improved by interdigital structure.In this thesis,the basic structure of Crossed field amplifier is introduced theoretically.The main function of Crossed field amplifier is composed of three parts: cathode module,slow wave structure and input/output structure.Then the different motion characteristics of electrons in electrostatic field and high frequency field are analyzed.In high frequency field,the generation process of electron spokes and anode current is analyzed.In this thesis,the slow wave structure of Crossed field amplifier is analyzed,and a new type of interdigital structure with different cavities is selected as the slow wave structure,and 22 different cavities are determined.Then,the high-frequency characteristics of the heterocavity structure and the interdigital structure were studied by CST to determine the appropriate size parameters.After determining 1/6 of the slow wave structure as the drift region,the energy transmission characteristics are studied.Finally,dumbbell impedance converter and ramp impedance gradient structure are adopted as input structure,and I-shaped impedance converter is adopted as output structure.Through the simulation and optimization of the energy transmission characteristics of the Crossed field amplifier,the working mode is the backward wave splitting mode of ? mode,.The optimized VSWR is less than 1.6 in the frequency band,and the signal transmission characteristics from the input port to the output port are good.Although the slow wave structure has only 19 cavities,the ? mode is still uniform.Based on the determination of the whole structure of Ka band Crossed field amplifier,the whole cavity is simulated by electromagnetic simulation software CST.Firstly,the simulation analysis is carried out in the state without high frequency signal input.With the increase of input signal power,the noise is effectively suppressed.Then the starting time of the input signal and the starting time of the working voltage are analyzed to determine the appropriate time relationship.Finally,particle simulation was carried out under the optimized model.12.2k V voltage and 1.1T axial magnetic field were applied between anode and cathode.The designed Ka band quadrature field amplifier achieves a gain of more than 11 d B between 35.98 GHz and 36.03 GHz.Due to the cross-finger structure of different cavity,and the working mode is the backwave splitting mode of ?mode,the bandwidth is narrow.At the frequency point of 36.03 GHz,the maximum gain is 17.9d B,achieving higher gain for Crossed field amplifier,while ensuring the advantage of low voltage.Ka-band Crossed field amplifiers remain between 31% and 36% efficient.