Chapter 6 - The Smith Chart

Abstract

The Smith chart is a means to perform graphical solutions to complex transmission line problems. The Smith chart consists of a series of orthogonal circles arranged around a central base line. The base line represents pure resistance, while one set of circles represents inductive reactance, and the other represents capacitive reactance. Pure reactances are graphed along an outer circle that is bisected by the pure resistance line. The circles that are tangent to the right side and bisected by the pure resistance line are constant resistance circles. Typical parameters that can be graphed or found on the Smith chart in transmission line problems are complex impedance, complex admittance, voltage standing wave ratio (VSWR), voltage reflection coefficient, power reflection coefficient, reflection coefficient angle, transmission coefficient angle, return loss (dB), reflection loss (dB), and transmission loss coefficient. The Smith chart can also be used for a variety of problems, including transmission line, impedance-matching stubs, tuned circles, and others involving complex impedances and/or frequency.