This is no longer just an "RF designer" issue, as the increase in clock speed of today's digital circuits, many are in the gigahertz range, means that the "pure" digital signals are actually in the RF domain. In RF circuits, matching the impedance between a source and load is critical to achieve effective power transfer with minimal loss, and avoid standing waves and reflections on transmission lines arising from the signal energy impinging on any impedance discontinuity. (Also note that the Smith chart can be used to graph multiport scattering parameters (S-parameters S 11, S 12, S 22, S 21), a standard tool for characterizing devices using vector network analysis, but that is another, much more complicated story.) So does test equipment it is also used extensively in RF/microwave network analyzers. While paper and pencil versions of it are, of course, less common than in the past, many datasheets and analysis and modeling application programs present data in Smith chart form. (Note that "Smith chart" is a registered trademark of Analog Instruments Company of New Providence, NJ.)Īlthough the Smith chart is one of the oldest tools in the RF kit, it is by no means obsolete, and is still used extensively in hands-on aspects of engineering. Its first public presentation was in a 1939 issue of Electronics magazine.
#Smith chart impedance matching how to#
It was developed in the 1930s by Phillip Hagar Smith at Bell Telephone Laboratories, who wrestled with the problem of how to show and evaluate multiple complex impedance parameters (which can range from zero to infinity) on a two-dimensional bounded graph.
The Smith chart is a valuable and often essential tool for anyone dealing with impedance issues in wired and wireless design at RF frequencies.
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