VSWR to return loss calculator
Enter any one of VSWR, return loss or reflection coefficient and the other two are calculated instantly, along with the mismatch loss and how much of the forward power actually reaches the load. The full conversion table from 1.00:1 to 10:1 is further down the page.
Enter any one value
Values are magnitudes only. A full reflection coefficient also has a phase term, which is what a Smith chart shows and what matters when you are designing a matching network.
Conversion formulas
All three quantities describe the same thing — how much of an incident wave bounces
back off a mismatched load. The reflection coefficient magnitude
|Γ| is the common link, so every conversion goes through it.
|Γ| = (VSWR − 1) / (VSWR + 1)VSWR = (1 + |Γ|) / (1 − |Γ|)RL(dB) = −20 · log10|Γ||Γ| = 10(−RL / 20)Mismatch loss(dB) = −10 · log10(1 − |Γ|²)Power delivered = (1 − |Γ|²) × 100% Return loss is quoted here as a positive number, which is the convention on almost every antenna datasheet: a larger figure means a better match. Some network analysers and simulators display the same quantity as a negative S11 in dB, so −20 dB of S11 and 20 dB of return loss describe the same match.
VSWR to return loss conversion table
Highlighted rows are the values that appear most often on antenna specifications. Mismatch loss is the power lost to reflection alone; it does not include cable, connector or dielectric losses.
| VSWR | Return loss | |Γ| | Mismatch loss | Power delivered | Power reflected |
|---|---|---|---|---|---|
| 1.00:1 | ∞ | 0.0000 | 0.00 dB | 100.00% | 0.00% |
| 1.01:1 | 46.06 dB | 0.0050 | 0.00 dB | 100.00% | 0.00% |
| 1.02:1 | 40.09 dB | 0.0099 | 0.00 dB | 99.99% | 0.01% |
| 1.05:1 | 32.26 dB | 0.0244 | 0.00 dB | 99.94% | 0.06% |
| 1.10:1 | 26.44 dB | 0.0476 | 0.01 dB | 99.77% | 0.23% |
| 1.15:1 | 23.13 dB | 0.0698 | 0.02 dB | 99.51% | 0.49% |
| 1.20:1 | 20.83 dB | 0.0909 | 0.04 dB | 99.17% | 0.83% |
| 1.25:1 | 19.08 dB | 0.1111 | 0.05 dB | 98.77% | 1.23% |
| 1.30:1 | 17.69 dB | 0.1304 | 0.08 dB | 98.30% | 1.70% |
| 1.40:1 | 15.56 dB | 0.1667 | 0.12 dB | 97.22% | 2.78% |
| 1.50:1 | 13.98 dB | 0.2000 | 0.18 dB | 96.00% | 4.00% |
| 1.60:1 | 12.74 dB | 0.2308 | 0.24 dB | 94.67% | 5.33% |
| 1.75:1 | 11.29 dB | 0.2727 | 0.34 dB | 92.56% | 7.44% |
| 2.00:1 | 9.54 dB | 0.3333 | 0.51 dB | 88.89% | 11.11% |
| 2.50:1 | 7.36 dB | 0.4286 | 0.88 dB | 81.63% | 18.37% |
| 3.00:1 | 6.02 dB | 0.5000 | 1.25 dB | 75.00% | 25.00% |
| 4.00:1 | 4.44 dB | 0.6000 | 1.94 dB | 64.00% | 36.00% |
| 5.00:1 | 3.52 dB | 0.6667 | 2.55 dB | 55.56% | 44.44% |
| 10.00:1 | 1.74 dB | 0.8182 | 4.81 dB | 33.06% | 66.94% |
What these numbers mean in practice
2:1 costs you half a decibel, so why does anyone care?
Read straight off the table, a 2:1 match throws away 0.51 dB — barely measurable in most link budgets. The mismatch itself is rarely the real problem. What matters is where the reflected 11% ends up: back into a transmitter output stage that may not tolerate it, into a circulator load, or into a receive chain where the mismatch shifts the low-noise amplifier away from the source impedance it was optimised for. A receiver’s noise figure can degrade by considerably more than the 0.51 dB of mismatch loss would suggest.
A specified VSWR is a worst case, not a typical value
When a datasheet says VSWR 2:1 over 30 MHz to 3 GHz, that is the ceiling across the whole band, and it is usually reached only at the band edges. Mid-band performance on a wideband antenna is often 1.3:1 or better. If your operating frequency sits near an edge, ask for the measured sweep rather than trusting the single headline figure.
A long cable makes a bad antenna look good
The most common measurement error. Cable loss attenuates the reflected wave on its way back to the instrument as well as the forward wave on its way out, so a return loss measured through a lossy cable reads roughly twice the cable loss too high. A genuine 2:1 antenna (9.54 dB return loss) measured through 3 dB of cable comes back as 15.54 dB — an apparent 1.40:1. Calibrate at the antenna port, not at the instrument port.
The same effect works in your favour when diagnosing a system: if a measurement looks suspiciously good on a long run, add twice the one-way cable loss back before believing it.
Antenna VSWR is not a fixed property
Unlike a coaxial component, an antenna’s input match depends on what is around it. Mounting brackets, a smaller-than-specified ground plane, nearby metalwork, radomes and even rain will all move the match. A biconical or log-periodic antenna measured on a test range at 1.5:1 can read 2.5:1 once bolted to a mast. Where the mounting is constrained, specify the match in the installed configuration.
Frequently asked questions
What is a good VSWR for an antenna?
For most commercial and EMC applications 2:1 or better across the operating band is considered acceptable, and 1.5:1 or better is good. High-power transmit systems and precision measurement setups typically call for 1.3:1 or better. Chasing a figure below 1.2:1 across a wide band usually costs bandwidth, size or money without improving system performance.
Is return loss the same as S11?
They describe the same reflection but with opposite signs. Return loss is quoted as a positive number where larger is better, while S11 is normally displayed as a negative dB value. A return loss of 20 dB and an S11 of −20 dB are the same match.
How much power is reflected at 2:1 VSWR?
The reflection coefficient magnitude is 0.333, so 11.11% of the incident power is reflected and 88.89% reaches the load. That corresponds to a mismatch loss of 0.51 dB.
What is the difference between mismatch loss and return loss?
Return loss describes how much power comes back from the load. Mismatch loss describes how much of the forward power fails to get into the load as a result. They are two views of the same reflection: 9.54 dB of return loss corresponds to 0.51 dB of mismatch loss.
Can VSWR be less than 1?
No. VSWR is the ratio of maximum to minimum voltage on the line, so its lowest possible value is 1.00:1, which is a perfect match with no reflection. A reading below 1 means the instrument is uncalibrated or the measurement is invalid.