What are VSWR and return loss?
VSWR (voltage standing-wave ratio) and return loss both quantify how well an antenna is matched to its feed line. With reflection coefficient Γ = (ZA−Z0)/(ZA+Z0), VSWR = (1+|Γ|)/(1−|Γ|) and return loss RL = −20·log10|Γ| dB; the power lost to reflection is the mismatch loss −10·log10(1−|Γ|²).[1] A 2:1 VSWR (RL ≈ 9.5 dB) costs about 0.5 dB.
How do VSWR, return loss and mismatch loss convert?
| VSWR | |Γ| | Return loss (dB) | Reflected power | Mismatch loss (dB) |
|---|---|---|---|---|
| 1.1 | 0.048 | 26.4 | 0.2% | 0.01 |
| 1.5 | 0.200 | 14.0 | 4.0% | 0.18 |
| 2.0 | 0.333 | 9.54 | 11.1% | 0.51 |
| 3.0 | 0.500 | 6.02 | 25% | 1.25 |
| 5.0 | 0.667 | 3.52 | 44.4% | 2.55 |
What VSWR is acceptable for an antenna?
Common specifications are VSWR ≤ 2:1 (RL ≥ 9.5 dB) for consumer and embedded antennas, ≤ 1.5:1 for base-station and infrastructure antennas, and tighter for test antennas. Some compact cellular antennas are specified at 3:1 at band edges because the Chu limit prevents better broadband match in the available volume.[2]
Is return loss positive or negative?
Return loss is defined as a positive number of dB, RL = −20·log|Γ|. Plots of S11 in dB are negative, and the two are often used interchangeably with a sign flip.[1]
Does good VSWR mean a good antenna?
No. A resistor has perfect VSWR and radiates nothing. Lossy cables also improve apparent VSWR at the transmitter because reflections are attenuated twice. Always check efficiency and pattern as well.[3]
Frequently asked questions
What return loss corresponds to VSWR 1.5?
About 14 dB.
Can VSWR be less than 1?
No; 1:1 is a perfect match.
Does feed-line length change VSWR?
In a lossless line VSWR is constant along the line; only the impedance seen rotates on the Smith chart.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Microwave Engineering, 4th ed.”. D. M. Pozar, Wiley. 2012.
- “Modern Small Antennas”. K. Fujimoto and H. Morishita, Cambridge University Press. 2013.
- “Antenna Theory: Analysis and Design, 4th ed.”. C. A. Balanis, Wiley. 2016.