VSWR Return Loss Calculator

How to use

1. 1Choose which quantity you already have: VSWR, return loss, reflection coefficient, or mismatch loss.
2. 2Type the value. VSWR accepts a plain number or a 1.5:1 style entry, and return loss accepts a positive or negative dB number.
3. 3Read the other three quantities, plus the percent of power reflected and transmitted, computed instantly.
4. 4Check the match quality note to see whether the value is excellent, acceptable, or poor for typical RF use.
5. 5Copy a single result or all results, or use the reference table to find a target VSWR or return loss.

About this tool

VSWR Return Loss Calculator converts between the four numbers that describe how well a radio frequency load, such as an antenna, a filter, an amplifier input, or a length of coax, is matched to the impedance feeding it. The four are different views of one underlying quantity, the magnitude of the reflection coefficient, usually written rho or the magnitude of Gamma, and the tool lets you enter whichever one you have and read the rest. Voltage standing wave ratio (VSWR, often shortened to SWR) is what an antenna analyzer or an SWR meter displays, and it runs from 1.0 to 1 for a perfect match upward with no upper bound. Return loss, in decibels, says how far below the forward wave the reflected wave sits, so a larger return loss means a better match; this tool reports it as a positive number because that is how matching targets are usually quoted, although some instruments print the same value with a minus sign. The reflection coefficient magnitude runs from 0 for a perfect match to 1 for a total reflection and is what a network analyzer shows as the magnitude of S11. Mismatch loss, also in decibels, is the through-loss caused purely by the reflection, that is, the power that never reaches the load because some of it bounces back, and it is separate from the cable's own attenuation. The relationships are exact and need no approximation: rho equals (VSWR minus 1) divided by (VSWR plus 1); VSWR equals (1 plus rho) divided by (1 minus rho); return loss equals minus 20 times the base 10 logarithm of rho; and mismatch loss equals minus 10 times the base 10 logarithm of one minus rho squared. From the same rho the tool also reports the fraction of incident power reflected, which is rho squared, and the fraction transmitted, which is one minus rho squared, expressed as percentages. A perfect match, rho of 0, is VSWR 1.0 to 1, infinite return loss, and zero mismatch loss; a total reflection from an open, a short, or a disconnected antenna, rho of 1, is infinite VSWR, 0 dB return loss, and infinite mismatch loss. Alongside the result the tool gives a plain reading of the match quality using the rules of thumb common in amateur radio and general RF work, where 1.5 to 1 is an excellent target, 2.0 to 1 is the usual limit for full transmitter power, and ratios beyond about 3.0 to 1 are poor and often trigger a transmitter to fold back its power to protect itself. A reference table lists the common values side by side so you can pick a target or sanity check a meter reading. Every result is computed in your browser with native logarithms and square roots. The value you type is never uploaded, logged, or stored.

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