定向耦合器 Directional Couplers

microwave101，干货比较多

传送门：https://www.microwaves101.com/encyclopedias/directional-couplers

Directional couplers are four-port circuits where one port is isolated from the input port. Directional couplers are passive reciprocal networks, which you can read more about on our page on basic network theory. All four ports are (ideally) matched, and the circuit is (ideally) lossless. Directional couplers can be realized in microstrip, stripline, coax and waveguide. They are used for sampling a signal, sometimes both the incident and reflected waves (this application is called a reflectometer, which is an important part of a network analyzer). Directional couplers generally use the distributed properties of microwave circuits. The coupling process generally occurs within a quarter-wavelength or multiple quarter-wavelength portions of the device. In these distributed couplers the energy and fields of one structure interact with the energy and fields of another distributed structure, coupling signals from one to another. Lumped element and hybrid couplers can be constructed as well. These couplers do not rely on the interaction of the fields and waves between transmission structures to create performance similar to that of coupled line structures but instead rely on networks composed of independent (un-coupled) circuit elements.

What do we mean by "directional"? A directional coupler has four ports, where one is regarded as the input, one is regarded as the "through" port (where most of the incident signal exits), one is regarded as the "coupled" port (where a fixed fraction of the input signal appears, usually expressed in dB), and one is regarded as the "isolated" port, which is usually terminated. On some commercial couplers the fourth (isolated) port is terminated internally or exterminally with a matched load - making a four port device seem like a three port device. If the signal is reversed so that it enter the "through" port, most of it exits the "input" port, but the coupled port is now the port that was previously regarded as the "isolated port". The coupled port is a function of which port is the incident port.

定向耦合器 ，盗图

wiki：https://en.wikipedia.org/wiki/Power_dividers_and_directional_couplers

wiki上是将功分器与定向耦合器放在一起介绍了，为啥？

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上面讲了一大堆，那么定向耦合器有什么作用呢

好了再贴一张盗图

所以只要在输入端口输入一定功率的信号，测试其它几个端口的信号，根据这些数据就可以计算出一堆参数

现在人很懒的，知道好多人数学不及格，计算器都帮我们写好了，http://www.rfwireless-world.com/calculators/Directional-Coupler-calculator.html

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那么为什么要计算这些参数呢？

所以一个伟大的仪器诞生了

当当当，裤裆掏出VNA，脑补图吧

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裤裆太小掏不出来怎么办？

拯救懒人世界的大佬又出现了

当当当

https://github.com/myriadrf/pyLMS7002M/tree/master/examples/VNA/doc

这篇说明由浅入浅讲述了VNA的基本理论并且给出了基于limesdr+python的实现方法