The Smith Chart

One of the distinctions that separates humans and animals is the ability of human race to create and use tools. From using flintstones to create fires, to cranes for building constructions, to software for designing. The invention of tools helps speed up and simplify the process of work, thus enabling more humans to handle more advance tasks easily and improving the quality of the work too.

A Tool For RF Designer

Similarly, when it comes to RF circuit designs, tools are also invented to improve the work performance. A commonly used tool is the Smith Chart. Used by students who are learning the RF circuit designs and even engineers handling advanced designs, the Smith Chart provides a simpler process for designing.

A Smith Chart is a graphical chart tool invented by the RF engineer Philip H. Smith. It consists of a real and imaginary plane arranged in a circular chart consisting of overlapping arcs. The Smith Chart can be split into 2 types. There’s the impedance and admittance Smith Chart. Visually, the admittance Smith Chart would be the vertically inverted version of the Impedance Smith Chart.

Its main help is found when designing the parameters related with transmission lines and its matching circuit. By determining the impedance/admittance from the Smith Chart (which is normalized to 1-ohm), parameters such as impedance, noise, stability, reflection coefficients (to name a few) can be found. But unlike an interactive software, it does not intuitively guide the user to find the answers they need. A designer would need to have knowledge on how to analyze and to understand the data provided by the Smith Chart for it to make sense.

Smith Chart in EDS

In these two part videos, we first demonstrate how some of the basic knowledge on how to use/analyze a Smith Chart using FILPAL EDS

Followed by how to do impedance matching using Smith Chart. Impedance matching is the process of matching the input and output impedance of a network. When unmatched, some of the input power and signal will be reflected back to the source. In another words, it means lesser efficiency of the system. A matched circuit will ensure full transmission from source to load. Check out the video below on how to perform impedance matching using a simple lumped element L-section matching network.