VSWR and S-parameters

VSWR (Voltage Standing Wave Ratio) is an indicator of signal reflection characteristics in coaxial cables. VSWR can be expressed as

Relationship between VSWR and S-parameters
S-parameters are metrics used to evaluate signal transmission and reflection in RF circuits and networks. In particular, S11 (return loss at the input port) is used as a parameter indicating reflection characteristics.
S-parameter S11 is defined as

from the voltage amplitude (VF) of the input signal and the voltage amplitude (VR) of the reflected wave. By rearranging the VSWR definition formula,

(|S11| is the absolute value of S-parameter S11) From the above equation, VSWR approaches 1 as the reflected wave (VR) becomes smaller, and becomes ∞ in the case of total reflection (VF = VR).
* Since network analyzers display S11 as a power ratio in dB, |S11| is calculated as follows:

VSWR is an important indicator in RF circuit design. Understanding VSWR enables you to suppress signal reflection and achieve efficient transmission.