Relationship Between Metrics
Return loss, VSWR, S11, and reflection coefficient all describe the same impedance mismatch — just in different units. Understanding how to convert between them is essential for reading datasheets and specifications from different vendors.
Return Loss (dB) = −20·log₁₀|Γ| [always positive, larger = better] S11 (dB) = 20·log₁₀|Γ| [always negative for passive] VSWR = (1+|Γ|)/(1−|Γ|) |Γ| = (VSWR−1)/(VSWR+1) Mismatch Loss = −10·log₁₀(1−|Γ|²)
Complete Conversion Table
| RL (dB) | S11 (dB) | VSWR | |Γ| | Mismatch Loss | Power Reflected |
|---|---|---|---|---|---|
| 6 | −6 | 3.01:1 | 0.501 | 1.25 dB | 25.1% |
| 8 | −8 | 2.32:1 | 0.398 | 0.75 dB | 15.8% |
| 10 | −10 | 1.92:1 | 0.316 | 0.46 dB | 10.0% |
| 12 | −12 | 1.67:1 | 0.251 | 0.28 dB | 6.3% |
| 14 | −14 | 1.50:1 | 0.200 | 0.18 dB | 4.0% |
| 16 | −16 | 1.37:1 | 0.158 | 0.11 dB | 2.5% |
| 18 | −18 | 1.29:1 | 0.126 | 0.07 dB | 1.6% |
| 20 | −20 | 1.22:1 | 0.100 | 0.04 dB | 1.0% |
| 22 | −22 | 1.17:1 | 0.079 | 0.03 dB | 0.63% |
| 25 | −25 | 1.12:1 | 0.056 | 0.01 dB | 0.32% |
| 30 | −30 | 1.065:1 | 0.032 | 0.004 dB | 0.10% |
| 40 | −40 | 1.020:1 | 0.010 | 0.0004 dB | 0.010% |
Common Specification Thresholds
| Application | Min Return Loss | Max VSWR |
|---|---|---|
| Mobile antenna | 10 dB | 1.92:1 |
| Base station antenna | 14 dB | 1.50:1 |
| RF filter port | 14 dB | 1.50:1 |
| Test cable (qualified) | 26 dB | 1.10:1 |
| SMA connector to 18 GHz | 20 dB | 1.22:1 |
RF View VSWR Calculator: Enter any value — VSWR, return loss, or S11 — in RF View's Utilities tab to get all other metrics instantly. Offline on Android.