【作者】 高喜；

【导师】 杨梓强；

【作者基本信息】 电子科技大学 ， 光学， 2009， 博士

【摘要】 高功率毫米波及亚毫米波在雷达、受控热核聚变波加热、通信、生物医学及材料科学等军事及民用领域有广泛的应用前景。Cherenkov器件是产生高功率电磁波辐射的有效手段,但是受物理机制的约束,工作到毫米波及亚毫米波段时,器件慢波系统的尺寸将变得很小,而这会使通过慢波系统的电子注受到限制,导致电流下降,因而难以实现高功率。相对论Cherenkov器件采用大尺寸过模结构的慢波系统,提高了电流容量,从而有效提高了辐射功率,但是模式竞争很难抑制。为了解决毫米波及亚毫米波段相对论Cherenkov器件的模式竞争问题,本论文提出基于金属光子带隙结构的新型慢波系统,利用其带隙特性,解决过模慢波系统中的模式竞争问题,从而提高器件的性能。其主要工作如下:1.采用时域有限差分(FDTD)方法研究了三角形及正方形金属光子带隙结构中TM极化波的能带特性。结果表明,无论是三角形晶格还是正方形晶格,TM极化波存在多个禁带区域,并且禁带之间存在明显的分界面,通过适当选取金属杆半径(r)与晶格常数(a)的比值,可使光子带隙结构中只存在唯一禁带。2.研究了金属光子带隙结构(PBG)单谐振腔特性。结果表明,合理选取腔体的结构参数,使腔体只支持TM01-like模式以及少数几个非对称模式,TM02-like模及更高阶的模式都不在腔体中存在;TM01-like模式的Q值主要受最内几层金属杆影响,通过减少外层金属杆层数,能有效降低高次通带模式的Q值,同时工作模式(TM01-like模)的Q值不受太大影响。3.提出了采用金属PBG腔构建Ka波段周期性慢波系统。对慢波系统中TM01-like模式的色散特性及电场分布特点进行了研究。为了快速获得色散曲线,提出用封闭圆边界慢波系统中TM01模式代替PBG慢波系统中TM01-like模式,并利用场匹配法推导出色散方程,数值计算结果表明:当封闭圆边界半径取PBG缺陷的平均半径时,TM01模式的色散曲线与模拟和实验结果基本一致。模拟仿真发现,由于PBG腔的边界呈现正六边形使得TM01-like模式的Ez场沿角向分布不均匀,从而导致耦合阻抗的角向不均匀性。利用三维粒子模拟手段,对PBG慢波系统中的注波互作用特性进行详细研究。研究结果表明:由于PBG结构的模式选择特性,显著降低了模式竞争现象,器件工作模式单一、频谱良好。4.为了改善慢波系统中工作模式电场在角向分布的均匀性,创新性提出了变态PBG慢波系统方案,该系统中PBG结构的最内层导体修正为圆排列的变态结构。研究了变态PBG慢波系统的色散特性、腔体Q值以及TM01-like模式场的角向分布等特性;利用PIC模拟方法研究了变态PBG慢波系统的辐射特性。研究结果表明,在变态PBG慢波系统中TM01-like模式的角向对称性得到显著改善,提高了器件的工作效率,有效抑制了非对称模式。5.对PBG慢波系统进行了详细的冷测实验研究。设计、加工了慢波系统谐振腔,冷测实验得到TM01-like模式的色散曲线与理论分析及模拟计算结果一致;进行了热测实验方案的研究,提出用磁绝缘同轴双阴极电子枪结构降低慢波系统的工作电流,利用PIC模拟方法对其进行了模拟研究;设计了输出耦合结构并进行了仿真分析。在此基础上,加工组装了用于热测实验的整体实验装置。更多还原

【Abstract】 High power millimeter wave and sub-millimeter wave have extensive applications in military and civil fields such as nuclear fusion heating, radar, communication, biomedical and material sciences. Cherenkov devices are always the effective means to produce high power electromagnetic wave. However, as the operation frequency increases to millimeter-wave and sub-millimeter range, the slow wave system (SWS) has small dimension so that power capacity will decreas correspondly. It is also very difficult to pass high current electron beam through such small structure. In relativistic Cherenkov device, the overmoded structure has been successfully employed to increase current capacity and radiation power but mode competition is difficult to be suppressed.To remove the mode competition of Cherenkov device in millimeter and sub-millimeter range, a metal photonic band gap (PBG) structure is employed to construct the novel SWS in this dissertation. Attributing to the mode selectivity of the PBG structure, the device can operate on single mode. The major achievements are follows:1. The global band gaps of TM polarization wave for general two-dimensional (2D) PBG structures formed by square or triangular arrays of metal posts are studied using finite-difference-time-domain (FDTD) code. The calculated results show that many band gaps of the TM polarization wave appear in triangular and square lattices and there is only one band gap in both lattices when the values of the ratio of the post radius (r) to the post spacing (a) in a certain range.2. The properties of a PBG cavity are investigated. The results show when the reasonable‘r’and‘a’are chosen, the PBG cavity only supports TM01-like mode and several other nonsymmetrical modes such as TM11-like and TM21-like modes. The higher-order TM0n-like modes are disappeared in the cavity. The Q value of TM01-like mode is determined by the inner posts of the cavity. Then, it is effective to decrease the Q value of high-order passing band mode by reducing the number of outer layer of lattice.3. A Ka-band SWS consisting of PBG cavity is proposed. The dispersion characteristic and the distribution of electric field of TM01-like mode in the PBG SWS are studied. To obtain the dispersion curve from the analytical theory, the opening boundary of the PBG structure is replaced by a closed boundary model with an appropriate radius equal to the average radius of the defect; and a dispersion equation is derived. According to the numerical calculations, the dispersion curve of TM01-like mode from the dispersion equation is in good agreement with the results of the simulation and experiment. Due to hexagonal boundary in defect, the Ez field of TM01-like mode has poor azimuthal symmetry and furthermore results in the poor azimuthal asymmetry of the coupling impedance. The results of 3-dimensional particle-in-cell (3D PIC) simulation show that the mode competition is depressed greatly in the Cherenkov source with PBG SWS. Single operation mode and radiation frequency are observed in PIC simulation.4. To improve the azimuthal symmetry of electric filed and coupling impedance of TM01-like mode, a SWS with modified PBG cavity is proposed. The inner post in modified PBG cavity is arranged in a circle. The interaction between electron beam and electromagnetic wave in the modified PBG SWS is analyzed by 3D PIC simulation. The results show that the azimuthal symmetry of the electric filed of TM01-like mode improves greatly. This improvement increases the efficiency of the device and restrains the asymmetry modes.5. Cold test experiments of the PBG and modified PBG SWSs are accomplished. The dispersive characteristics of the both SWSs obtained from cold test experiment are in good agreement with the numerical results, which demonstrates the reliability of the dispersion curve. In order to preserve the impedance matching between pulse power source and SWS, an electron gun with two-cathode is proposed to produce two-electron-beam. Only inner beam is used to drive the SWS and the outer beam is obsorbed by graphite plate. The characteristic of the gun is performed by 3D PIC simulation. On the other hand, the parameters of output system of high frequency structure are obtained by HFSS code. Based on these researches, the whole system for hot test is fabricated.更多还原