Input impedance of transmission line thumb|350px|Looking towards a load through a length of lossless transmission line, the impedance changes as increases, following the blue circle on this impedance Smith chart. (This impedance is characterized by its reflection coefficient, which is the reflected voltage divided by the incident voltage.) The blue circle, centred within the chart, is sometimes called an SWR circle (short for constant standing wave ratio).
Input impedance of tran?smission line thumb|350px|Looking towards a load through a length of lossless transmission line, the impedance changes as increases, following the blue circle on this impedance Smith chart. (This! impedance is characterized by its reflection coefficient, which is the reflected voltage divided by the incident voltage.) The blue circle, centred within the chart, is sometimes called an SWR circle (short for constant standing wave ratio).