波导

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波导，是一种用在微波波段中传输电磁波的装置，用于无线电通讯、雷达、导航等无线电领域。

在 电磁学 和 通讯工程, 波导 是一种用来引导电磁波传导的物理构架. 波导可被设计成传导电磁光谱的一部分波, 然而用于微波 和 光的 频率范围内波的传播更为常用. 根据频率的不同, 它可以用传导的 或者 电介质 材料制造. 波导被用于传递能量 和 通讯信号.

目录 1 历史 2 操作原理 3 空心金属波导 4 传输线 5 电介质波导 6 See also 7 External links 8 References

[编辑] 历史

1893年J.J.汤姆森第一个提出波导的概念。1894年O.J.洛奇第一个用实验证明了波导。1897年罗德·瑞利第一个完成了在空心金属圆柱形波导中传播模式的数学分析。(McLachan, 1947.)

[编辑] 操作原理

对波导的分析需要通过求解麦克斯韦方程组，或其推导形式，即电磁波动方程，再加上由材料及其界面性质所决定的边界条件。这组方程有多个解。每个解也叫做一个模，也就是本征方程组。因此每个模的特性由其本征值决定，而本征值与波在波导中轴传播速度有关。 波导传播的模取决于波长，偏振（极化），及波导的形状与大小。在空心金属波导中，对于矩形波导，基本模是transverse electric（横电波） TE_1,0模；对于圆形波导，基本模是TE_1,1。

矩形空心金属波导TE1,0模.

圆形空心金属波导TE1,1模.

[编辑] 空心金属波导

In the microwave region of the electromagnetic spectrum, a waveguide normally consists of a hollow metallic conductor. Hollow waveguides must be one-half wavelength or more in diameter in order to support one or more transverse wave modes. In some waveguides, there may be a positive pressure internally present, allowing for the detection of potentially dangerous RF leaks. Another solution to detect RF leakage of a waveguide is to have a vacuum present inside. Then leaks can be detected in basically the same way.

A slotted waveguide is generally used for radar and other similar applications. The waveguide structure has the capability of confining and supporting the energy of an electromagnetic wave to a specific relatively narrow and controllable path.

In physics and electronics every Klystron has a waveguide to process and propagating the transmitted RF output.

A closed waveguide is an electromagnetic waveguide (a) that is tubular, usually with a circular or rectangular cross section, (b) that has electrically conducting walls, (c) that may be hollow or filled with a dielectric material, (d) that can support a large number of discrete propagating modes, though only a few may be practical, (e) in which each discrete mode defines the propagation constant for that mode, (f) in which the field at any point is describable in terms of the supported modes, (g) in which there is no radiation field, and (h) in which discontinuities and bends cause mode conversion but not radiation.

[编辑] 传输线

For low frequency and RF applications, a variety of two-conductor waveguides exist, including open two-wire waveguides, coaxial cable, and microstrip transmission lines. A simplified analysis technique, transmission line analysis, can be used for many of these applications. There is no lower frequency limit for two-conductor waveguides, and they can conduct electromagnetic energy of frequencies all the way down to DC. Also, their diameter is not limited by wave propagation modes, so the transmission line thickness may be far narrower than one-half wavelength. All electric circuits function as waveguides of the transmission line type.

Several waveguides based on entrainment of EM waves also exist. These can take the form of single conductors with or without a dielectric coating, e.g. the Goubou line and helical waveguides. The same principle is used in dielectric rod waveguides, in linear arrays of short transverse conductors, and planar resistive conductors. These function via a refractive index effect where the waveguide slows the EM wave velocity below the free space velocity, continuously bending the EM wavefronts towards the waveguide and keeping them entrained. Helical waveguides and linear arrays of short conductors are used as part of "end-fire" antennas such as the helical antenna and Yagi antenna. Planar resistive waveguides are used in Over-The-Horizon radar and the Ground Wave Emergency Network, where the conductive surface of the Earth or ocean serves to entrain the waves and bend them around the curvature of the Earth. bbbbb

[编辑] 电介质波导

A dielectric waveguide is a waveguide that consists of a dielectric material surrounded by another dielectric material, such as air, glass, or plastic, with a lower refractive index. An example of a dielectric waveguide is an optical fiber. Paradoxically, a metallic waveguide filled with a dielectric material is not a dielectric waveguide.

In digital computing, the term waveguide can also be used for data buffers used as delay lines that simulate physical waveguide behavior, such as in digital waveguide synthesis.

[编辑] See also

• Angular misalignment loss
• Cutoff wavelength
• Dielectric constant
• Electromagnetic radiation
• Feedhorn
• Filled cable
• Horn (telecommunications)
• Leaky mode

• List of telecommunications transmission terms
• List of antenna terms
• List of fiber optic terms
• Klystron tube
• Radiation mode
• Radio wave
• Radio propagation
• Transmission medium

[编辑] External links

• Waveguides in particle accelerators incorporating Klystons

[编辑] References

This article is based in part on material from Federal Standard 1037C and from MIL-STD-188, and ATIS

• J. J. Thomson, Recent Researches (1893).
• O. J. Lodge, Proc. Roy. Inst. 14, p. 321 (1894).
• Lord Rayleigh, Phil. Mag. 43, p. 125 (1897).
• N. W. McLachlan, Theory and Applications of Mathieu Functions, p. 8 (1947) (reprinted by Dover: New York, 1964).