Enter any one of VSWR, return loss, reflection coefficient or mismatch loss and this VSWR calculator returns the others, along with how much power is reflected. Or start from a complex load impedance and a reference impedance, or from forward and reflected power readings.
Enter 2 for 2:1. VSWR is never below 1.
Optional: shows watts reflected and delivered.
Return loss
13.98 dB
Mismatch loss assumes a matched source. Line loss between the meter and the load makes the reading look better than the load really is.
VSWR = (1 + |Γ|) ÷ (1 − |Γ|), where |Γ| = |(ZL − Z0) ÷ (ZL + Z0)|. A 75 Ω load on a 50 Ω line has |Γ| = 0.200 and a VSWR of 1.5:1, which is a return loss of 13.98 dB, with 4.0 % of the power reflected and a mismatch loss of 0.18 dB.
All of these describe one quantity, the size of the reflection at the load. The reflection coefficient comes first; the others are different ways of stating it.
Power follows from |Γ|²:
|Γ| = (1.5 − 1) ÷ (1.5 + 1) = 0.200. Return loss is −20 log₁₀ 0.200 = 13.98 dB, 4.0 % of the power is reflected, and the mismatch loss is 0.18 dB.
Γ = j50 ÷ (100 + j50) = 0.200 + j0.400, so |Γ| = 0.447 at 63.4°. VSWR = 2.62:1, return loss is 6.99 dB and 20.0 % of the power is reflected.
With 100 W forward and 4 W reflected, |Γ| = √(4 ÷ 100) = 0.200, so VSWR = 1.5:1 and return loss is 13.98 dB. The load absorbs 96 % of the forward power.
VSWR table from 1.0 to 3.0, with the reflection coefficient and power split.
| VSWR | Return loss | |Γ| | Reflected | Delivered | Mismatch loss |
|---|---|---|---|---|---|
| 1.0 | ∞ dB | 0.000 | 0.00 % | 100.00 % | 0.000 dB |
| 1.1 | 26.44 dB | 0.048 | 0.23 % | 99.77 % | 0.010 dB |
| 1.2 | 20.83 dB | 0.091 | 0.83 % | 99.17 % | 0.036 dB |
| 1.3 | 17.69 dB | 0.130 | 1.70 % | 98.30 % | 0.075 dB |
| 1.4 | 15.56 dB | 0.167 | 2.78 % | 97.22 % | 0.122 dB |
| 1.5 | 13.98 dB | 0.200 | 4.00 % | 96.00 % | 0.177 dB |
| 1.6 | 12.74 dB | 0.231 | 5.33 % | 94.67 % | 0.238 dB |
| 1.7 | 11.73 dB | 0.259 | 6.72 % | 93.28 % | 0.302 dB |
| 1.8 | 10.88 dB | 0.286 | 8.16 % | 91.84 % | 0.370 dB |
| 1.9 | 10.16 dB | 0.310 | 9.63 % | 90.37 % | 0.440 dB |
| 2.0 | 9.54 dB | 0.333 | 11.11 % | 88.89 % | 0.512 dB |
| 2.2 | 8.52 dB | 0.375 | 14.06 % | 85.94 % | 0.658 dB |
| 2.5 | 7.36 dB | 0.429 | 18.37 % | 81.63 % | 0.881 dB |
| 3.0 | 6.02 dB | 0.500 | 25.00 % | 75.00 % | 1.249 dB |
Common return loss figures from data sheets and network analyzer limits.
| Return loss | VSWR | |Γ| | Reflected | Mismatch loss |
|---|---|---|---|---|
| 40 dB | 1.02:1 | 0.010 | 0.01 % | 0.000 dB |
| 30 dB | 1.07:1 | 0.032 | 0.10 % | 0.004 dB |
| 25 dB | 1.12:1 | 0.056 | 0.32 % | 0.014 dB |
| 20 dB | 1.22:1 | 0.100 | 1.00 % | 0.044 dB |
| 15 dB | 1.43:1 | 0.178 | 3.16 % | 0.140 dB |
| 14 dB | 1.5:1 | 0.200 | 3.98 % | 0.176 dB |
| 12 dB | 1.67:1 | 0.251 | 6.31 % | 0.283 dB |
| 10 dB | 1.92:1 | 0.316 | 10.00 % | 0.458 dB |
| 9.54 dB | 2:1 | 0.333 | 11.12 % | 0.512 dB |
| 6 dB | 3.01:1 | 0.501 | 25.12 % | 1.256 dB |
| 3 dB | 5.85:1 | 0.708 | 50.12 % | 3.021 dB |
| 1 dB | 17.4:1 | 0.891 | 79.43 % | 6.868 dB |
Return loss and VSWR both come from |Γ| and describe the same mismatch; neither says whether the load is high or low. A 2:1 VSWR on 50 Ω can be 100 Ω, 25 Ω or a complex load on the same circle, which is why matching a load needs the phase of Γ as well. Mismatch loss assumes a matched source: with a source that is also mismatched, the delivered power can be higher or lower depending on the phase of the two reflections. Cable loss between the meter and the load attenuates the reflection twice, so a long lossy feed makes a bad antenna read better than it is. The calculator treats Z0 as real, which is a good approximation for low-loss lines. Measure at the frequency you care about, since antennas and matching networks change quickly with frequency.
Voltage standing wave ratio: the maximum of the RF envelope on a line divided by its minimum. It equals (1 + |Γ|) ÷ (1 − |Γ|), and it runs from 1:1 for a matched load to infinite for full reflection. It is often shortened to SWR, which is the same ratio.
Find |Γ| = (VSWR − 1) ÷ (VSWR + 1), then return loss = −20 log₁₀ |Γ|. VSWR 1.5 is |Γ| = 0.200 and 13.98 dB; VSWR 2 is 0.333 and 9.54 dB. Enter either value in the VSWR to return loss calculator above.
Find |Γ| = (VSWR − 1) ÷ (VSWR + 1), then mismatch loss = −10 log₁₀ (1 − |Γ|²). VSWR 1.5 gives 0.18 dB and VSWR 2 gives 0.51 dB.
11.1 % of the forward power is reflected and 88.9 % reaches the load, a mismatch loss of 0.51 dB. At 3:1 it is 25.0 % reflected and 1.25 dB.
Return loss says how far the reflected signal is below the incident one, so a larger number is a better match. Mismatch loss says how much less power reaches the load because of the reflection, so a smaller number is a better match. Both come from the same |Γ|.
Keysight’s definition states it as a positive number: the decibels the reflected signal is below the incident signal. S11 in dB is the same magnitude with a negative sign, so an S11 of −14 dB is a return loss of 14 dB.
1.5:1, from Γ = (75 − 50) ÷ (75 + 50) = 0.200. Only 4.0 % of the power is reflected, a mismatch loss of 0.18 dB.
|Γ| = √(Pr ÷ Pf), then VSWR = (1 + |Γ|) ÷ (1 − |Γ|). With 100 W forward and 4 W reflected, |Γ| = 0.200 and VSWR is 1.5:1.
No. The maximum of the envelope cannot be below its minimum, so 1:1 is the lower limit. A reading below 1 means an error in the measurement or the calculation.
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