VSWR & Return Loss Calculator
Convert between VSWR, return loss, reflection coefficient, and mismatch loss. See reflected vs transmitted power.
About this calculator
This calculator converts Voltage Standing Wave Ratio (VSWR) into the other standard ways RF engineers describe an impedance mismatch. The reflection coefficient magnitude, Gamma = (VSWR - 1) / (VSWR + 1), is the fraction of the transmitted voltage wave reflected back toward the source; it runs from 0 at a perfect 1:1 match to approaching 1 as VSWR grows large. Return loss in dB is -20*log10(Gamma) -- a standard RF convention where a HIGHER return loss number means a BETTER match (more of the signal makes it through, less reflects), which is the opposite sense of most "loss" figures.
Mismatch loss, -10*log10(1 - Gamma^2), separately quantifies the power actually lost to the source from the mismatch rather than delivered forward, which is smaller than return loss suggests because reflected power isn't fully "lost" -- some of it re-reflects and eventually gets through, though this simplified two-port view doesn't model that re-reflection explicitly. Squaring Gamma converts the voltage reflection coefficient into power terms: reflected power is Gamma^2 of the incident power, and transmitted power is the complement. This calculator also reports the pair of resistive impedances (Z0 x VSWR and Z0 / VSWR, assuming a 50-ohm system) that would produce the entered VSWR if the mismatch were purely resistive -- a useful bounding reference, though a real antenna's mismatch is usually complex (resistive and reactive), not purely resistive.
Inputs
Results
Return Loss
13.98 dB
Reflection Coefficient (Γ)
0.2
Power Transmitted
96 %
How to Use This Calculator
- Enter the measured VSWR from your antenna analyzer (ideal = 1.0:1, acceptable <2.0:1).
- Set transmitter input power (W).
- Review return loss (dB), reflection coefficient, mismatch loss (dB), and reflected power percentage.
- VSWR above 2.0:1 reflects >11% power and may damage your transmitter -- investigate antenna connection.
- Use mismatch loss to quantify efficiency reduction from antenna impedance mismatch.
How the result changes with VSWR
| VSWR | Return Loss | Reflection Coefficient (Γ) | Power Transmitted |
|---|---|---|---|
| 1 | 60 dB | 0 | 100 % |
| 1.13 | 24.29 dB | 0.061 | 99.63 % |
| 2.25 | 8.3 dB | 0.3846 | 85.21 % |
| 3.75 | 4.75 dB | 0.5789 | 66.48 % |
What each input means
- VSWR
- Voltage Standing Wave Ratio (1.0 = perfect match, higher = worse)
- Input Power
- Transmitter power to calculate reflected/transmitted wattage
How this is calculated
Formula
Γ = (VSWR - 1) / (VSWR + 1); RL = -20·log₁₀(Γ)Worked example, using the default values
- Identify Input Parameters2 parametersVSWR = 1.5, Input Power = 100 = 2 input(s) provided
- Calculate Return LossReturn Loss13.98 = 13.98
- Calculate Reflection CoefficientReflection Coefficient0.2 = 0.2
- Calculate Power TransmittedPower Transmitted96 = 96
- Calculate Mismatch LossMismatch Loss0.177 = 0.177
- Calculate Power ReflectedPower Reflected4 = 4
Engine last updated . Checked against 4 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does a higher return loss number mean a better match, not a worse one?
Return loss is defined as -20*log10(Gamma), so a smaller reflection coefficient (a better match, closer to 1:1 VSWR) produces a LARGER return loss in dB -- a perfect match approaches infinite return loss. This is the opposite convention from most everyday "loss" terms, and it's a common point of confusion: in RF engineering, you want return loss to be a big number, not a small one.
What VSWR is considered acceptable for a transmitting antenna?
A VSWR of 2.0:1 or better is a commonly used practical target for amateur and commercial transmitting systems, corresponding to roughly 11% reflected power and about 9.5 dB return loss. Many transceivers will reduce power or shut down above that threshold to protect the final amplifier stage; a well-matched antenna system typically runs well below 2.0:1, often close to 1.0-1.5:1 at the design frequency.
Why isn't reflected power simply lost from the system?
Reflected power travels back down the feedline toward the transmitter, where -- depending on the source's own impedance match -- some of it re-reflects and continues toward the load again, rather than being fully absorbed or radiated away. This calculator's mismatch-loss figure treats the reflected fraction as forward power not delivered, which is the standard simplified two-port characterization; it does not model multiple internal re-reflections explicitly.
Are the high/low impedance values the actual complex impedance of my antenna?
No -- they're the two purely resistive impedances (Z0 times VSWR, and Z0 divided by VSWR) that would produce your entered VSWR if the mismatch had no reactive component. A real antenna's impedance is generally complex (resistance plus reactance), so these values are a useful bounding reference rather than a measurement of your actual feedpoint impedance.
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