Definition
Mismatch loss (ML) is the fraction of available power that is not delivered to the load due to impedance mismatch — the portion reflected back toward the source:
ML (dB) = −10·log₁₀(1 − |Γ|²) ML (dB) = −10·log₁₀(1 − 10^(S₁₁_dB/10)) Power delivered = P_available · (1 − |Γ|²) Power reflected = P_available · |Γ|²
Mismatch Loss vs VSWR Table
| VSWR | |Γ| | Return Loss | Mismatch Loss | Power Delivered |
|---|---|---|---|---|
| 1.0:1 | 0.000 | ∞ | 0.00 dB | 100% |
| 1.5:1 | 0.200 | 14.0 dB | 0.18 dB | 96.0% |
| 2.0:1 | 0.333 | 9.5 dB | 0.51 dB | 88.9% |
| 3.0:1 | 0.500 | 6.0 dB | 1.25 dB | 75.0% |
| 5.0:1 | 0.667 | 3.5 dB | 2.55 dB | 55.6% |
| 10.0:1 | 0.818 | 1.7 dB | 4.81 dB | 33.1% |
Mismatch Uncertainty in RF Measurements
Even after VNA calibration, residual port match (typically RL > 30–40 dB) causes measurement uncertainty. When measuring a DUT with high S11, the round-trip mismatch error can be significant:
Worst-case mismatch error (dB) = ±20·log₁₀(1 ± |Γ_source|·|Γ_DUT|) Example: |Γ_source|=0.05, |Γ_DUT|=0.4 → error = ±20·log₁₀(1±0.02) ≈ ±0.17 dB
RF View VSWR Calculator: Enter VSWR, return loss, or |Γ| in RF View's Utilities tab to instantly compute mismatch loss and the delivered power percentage. Offline on Android.