While the impedance smith charts are the most popular and the others rarely get a mention, they all have their “superpowers” and can be extremely useful when used interchangeably. Based on this scaling, smith charts can be categorized into three different types Smith chart is plotted on the complex reflection coefficient plane in two dimensions and is scaled in normalised impedance (the most common), normalised admittance or both, using different colours to distinguish between them and serving as a means to categorize them into different types. As a result of this, most RF Analysis Software and simple impedance measuring instruments include smith charts in the display options which makes it an important topic for RF Engineers.

Smith chart can be used to display several parameters including impedances, admittances, reflection coefficients, scattering parameters, noise figure circles, constant gain contours and regions for unconditional stability, and mechanical vibrations analysis, all at the same time. However, the Smith charts method of displaying data have managed to retain its preference over the years and it remains the method of choice for displaying how RF parameters behave at one or more frequencies with the alternative being tabulating the information. It was originally developed to be used for solving complex maths problem around transmission lines and matching circuits which has now been replaced by computer software. The Smith Chart, named after its Inventor Phillip Smith, developed in the 1940s, is essentially a polar plot of the complex reflection coefficient for arbitrary impedance. We will look into the types of smith chart, its construction and how to make sense of the data it holds.

For today’s tutorial, we will be looking at one of the tools that were developed back then and are still currently being used by engineer for RF designs, behold The Smith Chart. In today’s age with different software tools, things are a bit easier but if you go back to the periods before computers became this powerful, you will understand how difficult things were. RF Engineering is one of the most interesting and challenging parts of Electrical Engineering due to its high computational complexity of nightmarish tasks like impedance matching of interconnected blocks, associated with the practical implementation of RF solutions.

Impedance matching smith chart