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Smith Chart

In order to reduce the labour involved in calculations of the characteristics of a transmission line, different graphical techniques have been developed. The Smith chart is one such technique.

The Smith chart is a useful graphical tool used to calculate the reflection coefficient and impedance at various points on a (lossless) transmission line system.

The Smith chart is actually a polar plot of the complex reflection coefficient Γ(z) [ratio of the reflected wave voltage to the forward wave voltage] overlaid with the corresponding impedance Z(z) [ratio of overall voltage to overall current].

Applications of Smith Chart

A Smith chart can be used for the following purposes:
  • To find the normalised admittance from normalised impedance and vice versa
  • To find the parameters of mismatched transmission lines
  • To find the VSWR for a given load impedance
  • To find the reflection coefficient
  • To find the input impedance of a transmission line
  • To locate a voltage maximum on a transmission line
  • To design stubs for impedance matching

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