Research On Special Helix Slow-wave Structures

With the rapid development of military technology, helix traveling-wave tube(TWT)is increasingly used as a power amplifier in microwave band and millimeter wave band for many applications such as communication, radar and electronic countermeasures. Expanding the bandwidth and enhancing the power have been two of the most important development directions of the helix TWT. The technique of dispersion shaping contributes to improve the dispersion characteristics of helix slow-wave structure(SWS) so as to broaden the bandwidth of TWT. Higher output power and electronic efficiency can be obtained in designing the slow-wave circuit with technique of pitch tapered for TWT. The special helix SWSs are studied in this dissertation. The main contents are shown as follows:1. Based on technique of dispersion shaping, two structures with special support rod integrated by metal and dielectric are designed. The first structure is a helix SWS with special circular support rod and the second structure is a helix SWS with special rectangle support rod. The calculations and analysis of high frequency characteristics, beam-wave interaction characteristics and non-synchronization parameters of the two structures are presented. The results indicate that the first structure can produce output power 170~200 W with the gain over 40 dB, and the electronic efficiency can reach 10% ranging from 26 to 40 GHz. The second structure can produce output power 180~230 W with the gain over 47 dB, and the electronic efficiency is over 10% ranging from 26 to 40 GHz. The gain fluctuations of the two structures are both below 3 dB. The particle-in-cell simulation results show that the gain curve and the non-synchronous parameters curve are consistent with each other. The output power, gain and electronic efficiency produced by the second structure are higher than the first one so that the second structure is more suitable for the Ka-band helix TWT. The calculations including high frequency characteristics, beam-wave interaction characteristics and non-synchronization parameters for the second structure in V-band indicate that the structure can produce output power 60 W with the gain over 54 dB, and the electronic efficiency is over 8% ranging from 56 to 64 GHz. The integration of metal into dielectric can not only improve the mechanical strength of the support rod so as to enhance the stability of the SWS, but also can obviously improve the dispersion characteristics of the structure with expanding the bandwidth of TWT and can contribute to reduce the gain fluctuation of TWT.2. Based on technique of pitch tapered, the simulation analysis of beam-wave interaction characteristics of a TWT with helix SWS with fan-shaped vane-loaded is presented. By optimizing the slow-wave circuit with one attenuator and pitch tapered, the tube can produce output power 500 W and the electronic efficiency is over 18% ranging from 2 to 7 GHz at a cathode voltage of 5.4 kV and a beam current of 500 mA.