The Design Of The Ultra-wide Band Helix Traveling Wave Tube

Because of high output power, high efficiency and high gain characteristics, the wide band helix traveling wave tube(TWT) is widely used in radar, electronic countermeasures, communications and other fields. Especially, the development of electronic countermeasures technology requires helix TWTs to have a wider band and higher output power, so further study of widening the helix TWTs’ band and increasing its output power have vital theoretical and practical significance. In this thesis, a helix TWT with band width from 2 to 6 GHz is designed to achieve high power output. Design is focused on the high-frequency structure and the input/output coupler of the ultra-wide band helix TWT by simulation and experimental tests. The main work and innovation of the paper is as follows:1. The 2~6GHz TWT’s high-frequency structure is designed by HFSS software. After analyzing the impact on the size of the the fan blade parameters to the highfrequency characteristics, the goal which makes the slow-wave structure to get a flat dispersion in the ultra-wide band is achieved.2. The slow wave circuit is designed by ORION software. Focusing on the impact to beam-wave interaction with different phase-velocity tapering(PVT), the mechanism that positive PVT suppresses the second-harmonic growth is studied. It is verified through simulation. On this basis, A new negative-positive PVT technology is proposed, which can combine the negative PVT’s and the positive PVT’s superiority, and get a good solution to the contradiction between enhancing the fundamental wave output power and suppressing the second harmonic growth. It provides a new idea for ultrawide band TWT’s design.3. A new harmonic suppression technology- magnetic fields tapering technology is proposed. By using magnetic fields to change the form and quality of the electron beam, and the relative phase of harmonics, the growth of the second harmonic is effectively changed into fundamental power output. This technology explores a new approach for the design of TWTs. Meanwhile, by studying the radial velocity of the electron beam how to impact the beam-wave interaction. we try to achieve the target that makes fundamental wave output power to increase and the second harmonic to suppress.4.A optimized input/output coupler with good transmission characteristics is designed by modeling and simulating with CST software. In order to study how to achieve matching junction between input/output coupler and helix, a gradual smoothing connections is proposed, which can make the VSWR down to 1.27 in the entire working band. The method effectively enhances the transmission performance of the TWT.5.Comparing the theoretical simulation results and experimental data after product samples being tested, the data trends and the reasons for the differences is analyzed. After that, focusing on "serious defocus and a little fundamental output power at low frequency" in product samples being tesed, possible reasons is fully researched. It also provides suggestions to the development of the follow-up sample tube.