过模波导定向耦合器的研究与设计

发布时间：2019-03-13 17:06

【摘要】：定向耦合器是大功率微波系统中常用的一种器件,可以从系统中耦合出一小部分微波功率,用以监测及隔离大功率微波信号。定向耦合器可以由矩形波导、圆波导、微带线等多种传输线构成,并且主波导和副波导可以采用不同的传输线,设计方式多样,结构形式多样,并各有优缺点。现有的定向耦合器大多是基于单模传输情况下设计的。然而随着电子技术的发展,工业用微波系统的功率不断加大,基于单模传输的波导的功率容量在一些情况下难以满足要求,因而采用多种模式并存的过模波导成为一种解决办法,与其配套的过模波导定向耦合器的设计也因此成为一个课题。针对大功率微波系统应用需求,本文对过模波导定向耦合器进行了研究,分析了结构参数与电气参数间的关系,并对耦合器结构进行了设计。本文的主要工作可以概括为以下几点:1.对小孔耦合原理进行了阐述,对常用的定向耦合器主、副波导的类型进行了归纳,并对比了它们的优缺点。对定向耦合器的主要技术指标,包括耦合度、隔离度、方向性、驻波系数等进行了研究。分析了波导内部的场分布。2.对工作在2.4GHz的过模波导定向耦合器进行了研究与设计,为避免直接采用小尺寸耦合孔容易打火和出现耦合不稳定的问题,提出了采用过渡段的宽边耦合设计方案。主波导采用加大尺寸的BJ22矩形波导,过渡段采用标准的BJ22矩形波导,副波导则采用微带线以减小耦合器尺寸。首先分析了主波导内存在TE10、TE20、TE01三个模式情况下主副波导的场分布,以及结构参数对耦合度和方向性的影响。3.讨论了矩形波导尺寸进一步增大后产生的高次模的数量与比例,并对基于过模波导窄边和微带线直接耦合的耦合方式进行了研究。通过对耦合孔处电场分布的分析,验证了由波导窄边直接耦合到微带线的可行性。在此基础上,设计了一种能够承受大功率的基于窄边耦合的圆孔型过模波导定向耦合器,并对结构参数进行了优化。4.在仿真和分析过程中,由于波导内不可避免存在驻波,而定向耦合器的耦合度和方向性等参数理论上是在波导内存在行波状态下定义的参数,因此为了避免波导内驻波对定向耦合器电气参数设计带来影响,本文提出了一种利用坡印廷矢量积分计算功率、并对驻波影响进行修正的耦合度、方向性计算方法,分析了该方法的有效性。
[Abstract]:Directional couplers are commonly used in high-power microwave systems. A small portion of microwave power can be coupled from the system to monitor and isolate high-power microwave signals. Directional couplers can be composed of rectangular waveguide, circular waveguide, microstrip line and other transmission lines, and the main waveguide and the secondary waveguide can adopt different transmission lines. The design methods and structures of the directional couplers can be varied, and each has its own advantages and disadvantages. The existing directional couplers are mostly designed based on single-mode transmission. However, with the development of electronic technology, the power of industrial microwave system is increasing, and the power capacity of waveguide based on single-mode transmission is difficult to meet the requirements in some cases. Therefore, it is a kind of solution to adopt multi-mode co-existing over-mode waveguide, and the design of the directional coupler of the mode-pass waveguide has also become a subject. According to the application requirement of high power microwave system, this paper studies the directional coupler of over-mode waveguide, analyzes the relationship between structural parameters and electrical parameters, and designs the coupler structure. The main work of this paper can be summarized as follows: 1. In this paper, the principle of small hole coupling is described, and the types of main and secondary waveguide of directional coupling are summarized, and their advantages and disadvantages are compared. The main technical indexes of directional couplers, including coupling degree, isolation degree, directivity, standing wave coefficient and so on, are studied. The field distribution in the waveguide is analyzed. 2. The over-mode waveguide directional couplers working in 2.4GHz are studied and designed. In order to avoid the problem that small-size coupling holes are easy to fire and coupling instability occurs directly, a wide-edge coupling design scheme with transition section is put forward. The BJ22 rectangular waveguide is used in the main waveguide, the standard BJ22 rectangular waveguide is used in the transition section, and the microstrip line is used in the secondary waveguide to reduce the size of the coupler. Firstly, the field distribution of the main and secondary waveguides with three modes of TE10,TE20,TE01 in the main waveguide is analyzed, and the influence of structural parameters on the coupling degree and directivity is analyzed. 3. The number and proportion of higher order modes produced by further increasing the size of rectangular waveguides are discussed, and the coupling modes based on narrow edges of over-mode waveguides and microstrip lines are studied. Through the analysis of the electric field distribution at the coupling hole, the feasibility of direct coupling from narrow edge of waveguide to microstrip line is verified. On the basis of this, a circular cross-mode waveguide directional coupler based on narrow-edge coupling which can withstand high power is designed, and the structural parameters are optimized. 4. In the process of simulation and analysis, due to the inevitable existence of standing waves in the waveguide, the coupling degree and directivity of directional couplers are theoretically defined in the presence of traveling waves in the waveguide. Therefore, in order to avoid the influence of standing wave in waveguide on the design of electrical parameters of directional couplers, this paper presents a coupling degree and directivity calculation method, which uses Poynting vector integral to calculate power and modify the effect of standing wave on the design of electrical parameters of directional couplers. The effectiveness of the method is analyzed.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN622.2

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