How Do I Read a Smith Chart?

Focus on the inner circles. The outer circle in a Smith chart represents a coefficient of the

magnitude of one. Reflection-coefficient magnitudes cannot be more than one, so any area outside the outer circle has no bearing on the network in play. The other circles inside the outer circle represent the other coefficients of important variables, so they are the ones that impact the chart reading.

Learn the algebra. There is complex algebra involved with graphing Smith charts. This

mathematics relates to transmission lines, impedance, load resistance, reactance and other factors. The equations deal in ohms, which are units of energy, and the opposite, Siemens. The high-level algebra involved in graphic Smith charts makes up the foundation of what the charts show, so fully understanding the math will make reading a Smith chart easier.

Determine the orientation. Though there are different ways to orient a Smith Chart, the most common way puts the resistance on the horizontal axis and puts the location of the short circuit all the way on the left. This is because the voltage of a reflected wave during a short circuit has to cancel out that of an incident wave. This results in zero potential. Hence, angles in the Smith Chart are measured from the horizontal axis.

Look at how the lines of complex impedance and complex reflection relate to each other in the chart in order to see see how the two values impact one another. Any segments in the top half of the chart show instances of inductive reactance, and any on the bottom are capacitive reactances.