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Studies Of Coaxial Bragg Resonator Corrugated With Sinousoidal Ripples

Posted on:2012-06-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q XinFull Text:PDF
GTID:1118330338966646Subject:Computer application technology
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Because Bragg structure has excellent performances about mode choice and frequency selection, Bragg resonator composed of Bragg structure is widely adopted as open resonator in overmoded, high-power cyclotron auto-resonance maser (CARM) oscillators.In the early work, a lot of theoretical and experimental studies aimed at conventional cylindrical Bragg resonator and the analyses are based on single-mode, which lack systematic multi-mode coupling analysis for cavity performance. Due to coaxial waveguide displays many unique advantages in high-power free electron devices, coaxial Bragg structure has got more and more attentions. However, few scholars have studied on coaxial Bragg resonator which works well in high-frequency and high-power situation. Aiming at the problem, mathematic and physical model of Bragg structure are built based on scattering matrix method, and cylindrical and coaxial Bragg resonator's performances of single-mode and multi-mode coupling, transverse-electric (TE) mode and transverse-magnetic (TM) mode are comprehensively studied in this dissertation. The main contents are organized as follows:In Chapter 1, detailed research background about Bragg resonator is firstly introduced, and then main deficiencies about related works are analyzed. Aims as well as main contents of the present dissertation are also explained.In Chapter 2, the mathematic and physical model of scattering matrix method based on mode matching theory for coaxial Bragg structure is established. Firstly, scattering matrix method based on mode matching theory is introduced in coaxial Bragg structure, and computational formula of coupling coefficient between different modes, scattering matrix about cross section's abrupt change, and scattering matrix cascading are provided. Secondly, different cascading ways of scattering matrix applied in Bragg resonator are studied, detailed description is given about algorithm of two-dimensional scanning resonator frequency in complex frequency domain, and then recursion formula for getting field distribution at resonant frequency is deduced in this section. Finally, numerical simulation program is designed, and reported experimental data are used to validating the effectiveness about the mathematic and physical model.In Chapter 3, comparative research on single-mode analysis and multi-mode coupling analysis for cylindrical and coaxial Bragg resonator's performances is given. Firstly, Bragg reflector's single-mode phase-shift characteristic is studied. In accordance with the relationship between Bragg reflector's initial phase and phase-shift, a method to quickly design Bragg resonator is proposed. Secondly, comparison between single-mode analysis and multi-mode coupling analysis is carried out for studying the performances of Bragg resonator, and found that it is necessary to make multi-mode coupling analysis for Bragg resonator. Then, method of using multi-mode coupling analysis to optimize Bragg resonator is presented. Finally, comparative study for the performances of cylindrical Bragg resonator and coaxial Bragg resonator is carried out and found coaxial Bragg resonator with more advantages, such as more reasonable structure size, wider resonant frequency interval and better restrained spurious modes.In Chapter 4, coaxial Bragg resonator working in Terahertz frequency range, high-order TE mode is studied, designed and optimized. Firstly, comparative study for structure size and performance of coaxial Bragg reflector and cylindrical Bragg reflector working in Terahertz frequency range high-order mode is carried out and found that Bragg reflector not only has the structure size with larger crosswise direction and smaller lengthwise direction, which made coaxial Bragg reflector is appropriate for working in Terahertz frequency range high-power state, but also has better performance. Secondly, based on above study, high-order TE mode coaxial Bragg resonator working in 0.35 THz TE6.1 mode CARM oscillator is designed in detail, and comparative study is given between its single-mode analysis and multi-mode coupling analysis, and the optimization of resonator is made by using multi-mode coupling analysis, and finally get a coaxial Bragg resonator which can work well in Terahertz frequency range, high-order TE mode.In Chapter 5, coaxial Bragg resonator working in Terahertz frequency range, high-order TM mode is studied, designed and optimized. Firstly, comparative study for multi-mode coupling of coaxial Bragg reflector working in Terahertz frequency range high-order TM mode is carried out and shows that reasonable multi-mode coupling analysis is necessary for selecting high-order TM mode. Secondly, based on the appropriate high-order TM mode, coaxial Bragg resonator working well in 0.35 THz TM6.2 mode CARM oscillator is designed and optimized, and the feasibility of adopting high-order TM mode for CARM oscillator working in Terahertz frequency range is validated.In addition, all the aforementioned numerical approaches are programmed with Fortran language, and numerical examples in this dissertation are all calculated by these programs. The theoretical models, numerical programs and designed parameters are expected to provide theory basis and engineering references for the applications of coaxial Bragg resonator.
Keywords/Search Tags:Coaxial Bragg resonator, CARM, Mode matching theory, Scattering matrix, High-order mode, Multi-mode coupling analysis, Terahertz
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