2.10: Summary

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There are several network parameters used with RF and microwave circuits. Which is used depends on which makes the task of visualizing circuit operation more clear, which makes analyzing circuits more convenient, and which makes design easier.

Scattering parameters are parameters that are almost exclusively used by RF and microwave engineers. They describe power flow and traveling waves and are essential to describing distributed circuits. Much of RF and microwave engineering is concerned with managing the signal-to-noise power ratio and with power efficiency. It is therefore natural to work with parameters that directly relate to power flow. RF and microwave design is characterized by conceptual insight and it is essential to use parameters

Figure \(\PageIndex{1}\): Directional coupler schematic drawn with each of the four possible input ports.

and graphical representations that are close to the physical world. Scattering parameters have very natural graphical representations, as will be seen in the next chapter.

The next most important network parameters considered in this chapter are the \(ABCD\) parameters. The special significance of these parameters in microwave engineering is that they can be used to relate a distributed circuit to a lumped-element circuit. Many RF designs begin as lumped-element prototypes that are eventually transformed into electrically equivalent distributed structures. This equivalence process nearly always involves \(ABCD\) parameters.