Research On The Performance Of Helix Slow Wave Structure And Design For Application

Helix slow wave structure (helix SWS)is the most important slow wave system of the traveling wave tube (TWT). The good dispersion relationship, low phase velocity, high interaction impedance, and easy manufacture make the helix SWS widely used in modern military, including communication system, modern radar, electronic warfares and, etc. The investigations of the slow wave characteristics, frequency selective and storing energy characteristic are very useful for improving the performance of TWT and miniaturizing Rubidium Atomic Frequency Standards (RAFS).In this doctoral dissertation, the theoretical analysis and application design of the helix SWS have been investigated. We research on the performance of the helix SWS and its modified structures such as with loaded on the dielectric cylindrical or rectangular sup-port rods and sector shaped or T-shaped metallic vanes. Studying on the electromagnetic slow-wave system and field-match theory, we build up some theoretical models based on the spiral conducting surface. Using VBA program to process data and CST MWS mod-eling, the simulated results, including phase velocity, on-axis interaction impedance, and distribution of the electromagnetic field, are implemented and compared with the experi-mented results. The effect of the structure's parameters on the slow-wave characteristics are analyzed in detail and it can be referenced to the design of the helix SWS in TWT. At the same time, an improved helix SWS based on good propagation characteristics as a resonator for RAFS is designed. The effects of the different helical pitch and dielectric material in the insulator cylinder on the slow-wave characteristics are analyzed in detail. The main tasks and several valuable results are listed as following:(1) Based on the electromagnetic slow-wave system, a spiral conducting surface modeling of the single helix SWS is designed. The theoretical analysis is performed together with the simulations of the propagation characteristics. The distributions of elec-tromagnetic field are presented at the first time. Those conclusions can be the theoretical basis of the applying the helix SWS for RAFS.(2) For analysis of the dielectric support rods-loaded helix SWS, a helical tape model is built up by considering the width or thickness of the helix and the rods'shapes. The dielectric constant is calculated by the equivalent dielectric annulus. The dispersion re-lationship and interaction impedance of loading the cylindrical or rectangular dielectric support rods are gained by field-matched method. Considering the detailed effects of the helix width and thickness, several ways of optimizing structural parameters are proposed for improving the performance of the helix SWS.(3) The effects of different metallic vane-loaded helix SWS of TWT are proposed based on the analysis of Fourier expansions in the exterior region with metallic vanes. The influences of the metallic vanes dimensions on the phase velocity and interaction impedance are considered in detail. The computed data is compared with the reference data in the practical frequency range with a good consistency. The analytical results reveal that the method of using Fourier expansions can contribute effectively to the reducing of the error between the theoretical and experimented data. By analyzing the computed re-sults, the performances of the helix SWS, with T-shaped metallic vanes are superior to the sector-shaped with the same designed parameters. Adjustments can be made to the outer radius of T-shaped metallic vanes which then control the dispersion relationship showing either negative or positive, and it is similar to sector-shaped vanes by adjusting its inner radius. It is useful to design the helix SWS worked in the ultra high broadband.(4) Based on the simulation of the cylindrical resonator in RAFS using CST MWS models, the distribution of the electromagnetic field and the quality factor Q of TE111 mode are proposed. From analyzing the parameters, we design a miniaturized cavity with loaded the dielectric materials to compact the volume of RAFS. It is helpful to design a more smaller RAFS.(5) Based on the helix conducting surface model, the electromagnetic field equations of the helix SWS as the resonator cavity for RAFS is solved at the first time. An im-proved helix SWS based on good propagation characteristics as a helical resonator for RAFS is designed. The theoretical analysis is performed together with the simulations of the propagation characteristics. The simulated results, including phase velocity, on-axis interaction impedance, and distribution of the magnetic field, are implemented and compared with the experimented results. The effects of the different helical pitch and di-electric material in the insulator cylinder on the propagation characteristics are analyzing in detail. The analyzed results show that smaller helical pitch and proper usage of dielec-tric material in the insulator cylinder can make the propagation characteristics of the helix SWS superior. Then a heating circuit of temperature stability is designed to weaken the cavity-pulling effect. The improved helix SWS have been applied in RAFS and the rela-tion parameters, including the resonant cavity's resonance line, frequency stability, SNR, and temperature stability are all achieved.