| TWT play an important role in the field of microwave and millimeter-wave evidently. The defense and civilian field both need them because it can achieve a high average power, its energy efficiency is relatively high, and the other factor is its band width is much wider than semiconductor devices now. TWT are often specialized in these critical devices of major projects of country each year. Helix traveling wave tube and coupled cavity traveling wave tube are often used in the most applications. In the order to transfer the high-frequency electromagnetic signal, there is how the high -frequency electromagnetic signals trans to the slow wave structure, which requires input and output structure. Slow-wave structure and the input - output structure are the different structure, so there is the electromagnetic field conversion between the different transmission structure and impedance matching and a series of problems. Paper make some research base on the previous researchers and make the following work mainly:1. Establish the slow-wave structure of simulation models. according to the parameters of Helix traveling wave tube, establish the helix slow wave structure model, and c optimization the model, in order to it can work in the 6 ~ 18GHz frequency bands; when establish the slow-wave structure, first of all, when dealing with helix, cutting the helix in three section, the simulation results show that this method can effectively reduce the slow-wave structure in the low frequency impedance, it is easy to match between slow wave structure and the structure of input-output on impedance .Second, explore the suitable connection structure between input and output structure and slow-wave structure . Finally, using the Ansoft HFSS (High Frequency Structure Simulator) software simulate the model of the slow wave structure, and get the inherent properties of slow wave structure, including: S parameter (S11, S21), and the VSWR (Voltage Standing Wave Ratio) and so on.2. Establish the coaxial window model. Using HFSS software, establish the coaxial window model.. First calculated the coaxial radius and the radius of the vacuum using a model coaxial in theory, and then use HFSS to scan for sensitive parameters, and get the optimum performance parameters of the model parameters. Last, scan S parameters (S11, S21), and the VSWR (Voltage Standing Wave Ratio) and so on.3.Connect the coaxial input -output structure and the helix traveling wave tube, and simulate them, observation the disturb input-output structure of coaxial to helix slow wave structure on the inherent performance parameters (including S parameters and VSWR parameters) , if the disturb is very little, it shows that the input-output structure is suitable to helix traveling wave tube.4. According to the parameters of coupled cavity structure, using Ansoft HFSS (High Frequency Structure Simulator) software to establish the coupling cavity model, and scan the performance parameters in the work bandwidth, including: S parameters and VSWR parameters.5. According to the box-shaped windows theory we can determine the structure parameters of the rectangular waveguide and cylindrical waveguide and the medium size, and then using Ansoft HFSS (High Frequency Structure Simulator) software scan the sensitive parameters to obtain structure parameters.This paper's innovation is reflected in the following points:1. Design the traveling wave tube, which working bandwidth is 6-18GHz, paper works through the following points to improve the performance parameters: first, dividing the overall helix into three sections. The first section's pitch is 1.6mm, the second section's pitch is 1.9mm, and the third section's pitch is 1.9mm. The first section and the third section have three turns helix respectively. This can be a good result to performance of helix structure. Second, we change the coaxial to slow-change coaxial for good matching. Third, we change the structure of connecting coaxial and helix to improve the matching performance. we change the structure to a rectangular shape, the rectangle's cross section is same to the helix's cross section, the coaxial is slow-change, the top section is cylinder, the following is a round-shaped, we make the helix's cross section's circumcircle is the round-shape's underside. This change can lead to good matching between coaxial and helix.2. During the design process of coaxial structure, I scan the structure parameters which make the performance parameters change quickly. Then scan the sensitive structure parameters in different section. This make us know how the VSWR change when the structure change in different frequency. 3. During the design process of box-shaped windows, first we use the theoretical calculations and get the initial parameters of the model, then build the structure using HFSS, and simulate the model to get the sensitive structure parameters to performance parameters. We obtain the different performance parameters when the structure parameters change. This is useful to actual design. Second, we change the ration between the rectangular waveguide's wide side and narrow side into 0.45. This make the structure can work at 61-70GHz frequency showing that working-frequency wider, this structure can suitable for other couple-cavity structure when we change the transition structure. Change the side ratio of rectangular waveguide to adjust the bandwidth for us to provide a reference. |
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