Formula
S11 (dB) → |Γ| → VSWR
Step 1: |Γ| = 10^(S11_dB / 20)
Step 2: VSWR = (1 + |Γ|) / (1 − |Γ|)
Example: S11 = −14 dB
|Γ| = 10^(−14/20) = 10^(−0.7) = 0.200
VSWR = (1 + 0.200) / (1 − 0.200) = 1.200 / 0.800 = 1.50:1
Key Conversion Table
| S11 (dB) | |Γ| | VSWR | Power Reflected |
|---|---|---|---|
| −6.0 | 0.501 | 3.01 | 25.1% |
| −9.5 | 0.335 | 2.00 | 11.2% |
| −10.0 | 0.316 | 1.92 | 10.0% |
| −14.0 | 0.200 | 1.50 | 4.0% |
| −20.0 | 0.100 | 1.22 | 1.0% |
| −26.0 | 0.050 | 1.11 | 0.25% |
Automated Methods
- RF View VSWR view: Load .s1p/.s2p → switch from S11 dB to VSWR → trace immediately shows VSWR vs frequency
- RF View VSWR calculator: Utilities tab → enter S11 dB value → get VSWR instantly
- RF View BW Marker in VSWR mode: Automatically finds BW where VSWR < 2:1 (or any threshold)
When to Report VSWR vs Return Loss
Both convey the same information — choose based on audience and convention:
- Antenna engineering: VSWR is traditional (datasheet says "VSWR < 2:1")
- Filter/amplifier engineering: Return Loss preferred ("RL > 14 dB")
- VNA plots: S11 in dB is most common on-screen
- Transmitter design: VSWR common (PA protection specification)
RF View: Switch between S11 dB, Return Loss, and VSWR views with one tap. No manual calculation needed. BW Marker finds VSWR=2:1 bandwidth automatically. Free on Android.