What third family of circles is often added to a Smith chart during the process of designing impedance matching networks?

A standard Smith chart is primarily composed of two sets of lines: circles of constant resistance and arcs of constant reactance. When designing impedance matching networks, a third set of circles, known as constant-SWR (Standing Wave Ratio) circles, is often drawn onto the chart. These circles are centered on the prime center of the chart, which represents a perfect match (an SWR of 1:1). Any point resting on a specific constant-SWR circle represents an impedance that will yield that exact SWR on the transmission line, helping engineers visualize how well a matching network minimizes reflected power.