VSWR Calculator

How it is calculated

VSWR (voltage standing wave ratio) describes how well an antenna or load is matched to its transmission line. From the reflection coefficient magnitude Γ the tool computes VSWR = (1 + |Γ|) ÷ (1 − |Γ|) and the return loss RL = −20 × log10(|Γ|) in decibels. Γ is a plain number from 0 to just below 1: 0 means a perfect match and values near 1 mean almost everything is reflected. Values below 0, or 1 and above, give no result. At Γ = 0 the VSWR is 1 and the return loss is shown as infinite. VSWR is dimensionless and always 1 or greater; a larger return loss means a better match.

Common mistakes

• Entering the reflection coefficient as a percentage (20) or in decibels. The field takes a plain magnitude between 0 and 1.
• Entering the VSWR value itself, such as 1.5, as Γ. That is greater than 1 and returns nothing.
• Mixing up return loss and reflected power. 14 dB return loss does not mean 14% reflected; the reflected power is Γ squared.
• Reading a high return loss as bad. Higher return loss is better, since less power comes back.
• Measuring at the transmitter instead of at the antenna. Cable loss hides reflections and makes the VSWR look better than it is.