Formulas
| Reflection coef. Γ | = (Z_L − Z_0) / (Z_L + Z_0) |
|---|---|
| Return loss | = −20 · log₁₀(|Γ|) (dB, positive number) |
| VSWR | = (1 + |Γ|) / (1 − |Γ|) |
| |Γ| | = (VSWR − 1) / (VSWR + 1) |
| Power reflected | = |Γ|² · P_incident |
Quick table
| VSWR | Return loss | |Γ| | Power reflected |
|---|---|---|---|
| 1.0 : 1 | ∞ dB | 0 | 0% |
| 1.1 : 1 | 26.4 dB | 0.048 | 0.23% |
| 1.2 : 1 | 20.8 dB | 0.091 | 0.83% |
| 1.5 : 1 | 13.9 dB | 0.200 | 4.0% |
| 2.0 : 1 | 9.5 dB | 0.333 | 11.1% |
| 3.0 : 1 | 6.0 dB | 0.500 | 25% |
| 5.0 : 1 | 3.5 dB | 0.667 | 44.4% |
| 10 : 1 | 1.7 dB | 0.818 | 66.9% |
| ∞ : 1 | 0 dB | 1.0 | 100% (short or open) |
Guidelines
| Excellent match | VSWR ≤ 1.2 (RL ≥ 20 dB) |
|---|---|
| Good match | VSWR ≤ 1.5 (RL ≥ 14 dB) |
| Acceptable | VSWR ≤ 2 (RL ≥ 10 dB) |
| Bad — transmitter at risk | VSWR > 3 |
Notes
- Most transmitters fold-back or shut down above VSWR ~2:1 to protect output stages.
- Conjugate match maximizes power delivered; equal impedance minimizes reflections. For 50 Ω / 75 Ω real systems they coincide.
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