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VSWR Calculator

Find VSWR and return loss.

Result

1.5000
13.98 dB

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.

Worked example

Suppose a measurement gives a reflection coefficient of 0.2. VSWR: (1 + 0.2) ÷ (1 − 0.2) = 1.2 ÷ 0.8 = 1.5000. Return loss: log10(0.2) is about −0.699, so −20 × (−0.699) gives 13.98 dB. A VSWR of 1.5 is generally considered a good match, with only 4% of the power reflected (0.2 squared).

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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.

Sources

About this calculator

Voltage standing wave ratio is calculated as VSWR = (1 + |Γ|) / (1 − |Γ|), where Γ is the complex reflection coefficient produced when a transmission line's impedance doesn't match the load — typically an antenna. A perfectly matched system has Γ = 0 and VSWR = 1:1, meaning no power reflects back toward the source, while higher VSWR values indicate standing waves caused by reflected energy bouncing between source and load.

RF and antenna engineers measure VSWR to verify that a transmission line, connector or antenna is properly matched before transmitting at power, since a poor match reflects energy back into the transmitter, wastes power and can overheat or damage amplifier components. Amateur radio operators, cellular site technicians and satellite communications engineers routinely check VSWR with a directional coupler or antenna analyzer, generally aiming to stay below 2:1 for efficient operation.

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Comments (1)

  • Editorial team

    Most antenna analysers display VSWR directly, while this tool asks for the reflection coefficient. Convert first: Γ = (VSWR − 1) ÷ (VSWR + 1). A 2:1 reading is Γ of about 0.3333, which the tool turns into a return loss of 9.54 dB and about 11 percent reflected power. Enter that Γ to see the matching figures. What VSWR are you trying to reach on your antenna?

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