VSWR is used to measure the change in voltage and is the ratio of the highest voltage to the lowest voltage on the transmission line. Since the voltage in the ideal system remains the same, the corresponding VSWR is 1:1. When reflection occurs, the voltage changes and the VSWR increases -- for example: 1.2:1 or 2:1.
Voltage standing wave ratio calculation formula:
VSWR is the voltage ratio on the transmission line:
VSWR = |V(max)|/|V(min)|
Where V(max) is the maximum value of the signal voltage on the transmission line, and V(min) is the minimum value of the signal voltage on the transmission line.
It is also possible to use impedance calculations:
VSWR = (1+Γ)/(1-Γ)
Where Γ is the voltage reflection coefficient close to the load end, determined by the load impedance (ZL) and the source impedance (Zo):
Γ = (ZL-Zo)/(ZL+Zo)
If the load exactly matches the transmission line, Γ = 0, VSWR = 1:1
