Smith Chart

 

Smith's chart contains information on parameters such as impedance scattering, noise which are used In RF measurements. Philip Smith introduced this chart with the idea of having graphical calculations. Although most of the tasks are now performed using software but still many radio frequency measurements where frequency needs to be matched, a smith chart is preferred instead of other tables as graphical representation present a better illustration for the user. Smith chart is also known as 1 port scattering parameter chart as it displays polar complex, reflex coefficient information. The refection coefficient, say for example, for a lossless lien can be calculated is given by:

 

Figure 1 Smith Chart

Source:

https://commons.wikimedia.org/wiki/File:Smith_chart_gen.svg

you may find these charts in three different categories including:

Impedance Chart is used with large loads where the impedance matching is crucial, and many RF technology also uses this chart to properly match the impedance for the antennas.

Admittance Chart is used in the parallel circuit, contrary to the impedance chart where series loads are used. This chart simplifies a parallel circuit's complication where inductive and capacitive loads are sued in a parallel configuration.

Immittance Chart are used where a complex combination using both parallel and series circuits is used. It works because it plots the impedance and admittance charts on one above the other to present a better graphical view.

Benefits of Smith Chart:

A smith chart has the following uses when visually interpreting frequency ranges;

1-      It can demonstrate how well a component is matched to a corresponding frequency.

2-      The behavior and impedance match at various frequency levels.

3-      The captative and inductive load behavior over the frequency ranges.

Applications:

Smith chart is still used for many applications, including the following:

·         Matching of impedance and design for matching network.

·         Allows graphical solution instead of using high computing software.

·         Helps visualize the behavior of the impedance loads such as inductive and capacitive loads over the frequency ranges.

·         Helps in tuning and verification of frequency matching designs.

To summarize, the smith chart is used to visualize and understand the complex impedance values and help match the frequency ranges' impedance.