Simulation Of A Novel Cold Cathode Coupled Cavity Traveling Wave Tube

Compared with the hot cathode,the carbon nanotube cold cathode has the advantages of smaller volume,working at room temperature,low production cost and so on.Using carbon nanotube cold cathode to develop miniaturized electric vacuum devices has become a hot topic at home and abroad.In this paper,the miniaturization of Ka band carbon nanotube cold cathode coupled cavity traveling wave tube is studied in view of the development demand of miniaturization of microwave and millimeter wave devices.With the help of electromagnetic simulation software,based on the same size coupled cavity slow wave structure and the same number of cycles,the hot cathode traveling wave tube without pre-modulated electron beam and carbon nanotube cold cathode traveling wave tube with pre-modulated electron beam were simulated.The main research work in this paper is as follows:1.A novel cold cathode coupled cavity traveling wave tube carbon nanotube electron gun used in Ka band is designed.Based on the field emission theory,combined with the field emission mechanism of carbon nanotubes,a parallel plat microstrip-like carbon nanotube electron gun was built in the three-dimensional electromagnetic simulation software CST.First,the transmission characteristic and emission characteristic of the electron gun are studied.The results show that the transmission characteristic and emission characteristic of the carbon nanotube electron gun are good.Then the modulation current size and modulation depth are calculated.By changing the grid voltage,the size and modulation depth of the modulation current are studied.The results show that the larger the grid voltage is,the greater the modulation current of the carbon nanotube electron gun is,the greater the modulation depth is.2.The size parameters of the slow wave structure of the coupled cavity are designed.Firstly,the simulation model of coupled cavity slow wave structure is established.Combined with the dispersion theory of slow wave system and the theory of coupling impedance,the coupled cavity slow wave structure is optimized.The influence of the main size parameters on the slow wave characteristics of the coupled cavity slow wave structure is discussed,and the size parameters of the coupled cavity slow wave structure are finally determined.3.Particle simulation of carbon nanotube cold cathode coupled cavity traveling wavetube.In the three-dimensional electromagnetic simulation software CST,a beam wave interaction circuit model of a coupled cavity traveling wave tube with a period of 20 is established.The hot cathode coupled cavity traveling wave tube without pre-modulated electron beam is simulated firstly,in which the electronic emission mode adopts the ideal direct current mode.Then,the particle simulation of the carbon nanotube cold cathode coupled cavity traveling wave tube with pre-modulated electron beam is carried out,in which the electron emission mode uses the field emission mode of carbon nanotubes.Their input,output signal amplitude,spectrum,and electron cluster are analyzed and discussed respectively.The results show that the output power and gain of the CNT coupled cavity TWT are larger than the output power and gain of the hot cathode coupled cavity TWT without pre-modulated electron beam.