Study On High Frequency Coupling System Of Q - Band Coupling Cavity Traveling Wave Tube

The energy coupling system of the Q band coupled cavity traveling wave tube(CCTWT) was investigated by using a mircrpowave simulation tools,Microwave studio CST. The coupling system that connecting the slow wave strucyure(SWS) and the BJ-400 standard rectangular waveguide were design and optimized. The electric parameters of the coupling system were determined after a number of numerical calculation and analysis.A engineering prototype traveling wave tube was developed to validate the performance of the coupling structure.Different types of the waveguide transitions were analyzed and compared. Given the value of voltage standing wave ratio(VSWR) and bandwidth,the linear tapered waveguide transition has the longest length. The length of the dual-arc waveguide transition is shorter and the length of the step tapered waveguide transition is shorest. Howerer,the fabricating process of the dual-arc tapered waveguide is most difficult in the three types of waveguide. The fabricating process of step taped waveguide is easier and the linear and the linear tapered waveguide is the easiest one. Consider the fabricating difficult and practical facor, the linear tapered waveguide transition was closen in the experiment.The iris length and coupling slot angle of the coupling cavity were adjusted to obtain an optimal match between SWS and the linear tapered waveguide transition. The match is good when the kidney shape coupling slot is set close to the shorting plane. The slot angle of the coupling cavity should be little larger than the slot angle in ordinary SWS. The parameters need to be optimized are including the coupling slot angle, the length and radius of the inner and outer iris and the thickness of the coupling cavity wall. The design of the energy coupling system should be verified by experiment.Owing to the lake of time and the difficult of fabricating way,only input part of the energy coupler was produced. The cold test results show the VSWR of the input energy coupler is little high than the simulation but the difference is small. It prove the valid of the design and simulation. The difference between experiment and simulation is due the error in component processing error and assembling.