Electromagnetic Simulation And Design Of Multi-gap Coupled Cavity

The Extended Interaction Klystron is the introduction of a multi-gap coupling cavity in a conventional klystron,so that the extended interaction klystron are more likely to achieve greater output power,gain and bandwidth in the high frequency band to meet the modern equipment.The multi-gap coupled cavity is a key technology for the development of extended klystrons.In this paper,Based on the existing equivalent circuit,the basic principle of microwave network and the basic theory of space charge wave,the three-dimensional electromagnetic simulation software is used to analyze the theoretical analysis and numerical simulation of resonant frequency,characteristic impedance,mode overlap and stability in the coupling cavity:Based on the basic principle of microwave network,the basic model of multi-gap coupling cavity equivalent circuit is obtained by combining the equivalent method of electromagnetic lumped parameters of resonant cavity.Taking the three-gap coupling cavity as an example,the resonant frequency and the characteristic impedance of the coupling cavity are analyzed with the coupling resonant frequency and the coupling coefficient.The resonant frequency and its corresponding characteristic impedance are calculated by adjusting the size and position of the coupling slot.The results show that the coupling slot angle plays a dominant role in the mode frequency distribution and its characteristic impedance value,and the coupling position is different for each mode characteristic impedance.The coupling width is mainly affected by the resonant frequency of each mode.Combining the cold parameters and the structural dimensional variation of the different modes in the coupling cavity,the final optimization is obtained from the resonant frequency and the characteristic impedance.At the coupling angle of 105°,the first three modes(-? mode,-?/2 mode,2? mode)overlap,the coupling angle in 225° the later three modes(? mode,?/2 mode,2? mode)overlap state,the corresponding characteristic impedance amplitude is relatively large.Based on the theory of space charge wave,the formula of multi-gap coupling cavity electron injection is obtained.According to the three-dimensional electromagnetic simulation software,the characteristic impedance of each mode in three multi-gap coupling cavity is obtained.By calculating the reciprocal of quality factor of each mode,in this paper,the change of DC voltage with each mode is analyzed under the premise of two kinds of multi-mode overlap.It is pointed out that the injection-wave synchronization is the key factor to realize the stable operation.The working voltage of 20kV can achieve three working modes and the other modes are also easy to be suppressed.