The 8 Most Common VSWR Problems
| Cause | VSWR Symptom | Fix |
|---|---|---|
| Impedance mismatch (design) | VSWR >2:1 at all frequencies | Add matching network |
| Damaged coaxial cable | VSWR spikes at specific frequencies | Replace cable |
| Corroded/damaged connector | Irregular VSWR, varies with connector position | Clean or replace connector |
| Antenna too electrically short | Capacitive locus on Smith chart (lower half) | Lengthen antenna or add series inductor |
| Antenna too electrically long | Inductive locus (upper half of Smith chart) | Shorten or add series capacitor |
| Small ground plane | High VSWR, also poor efficiency | Extend ground plane or add counterpoise |
| Nearby metal detuning antenna | VSWR good in free air, bad when mounted | Tune antenna in final mounted position |
| Wrong target frequency | VSWR >2:1 except at design resonance | Use antenna designed for your frequency |
VSWR Troubleshooting Flowchart
- Measure S11 with VNA (not just a power meter VSWR bridge) → get frequency-resolved data
- Disconnect cable from antenna: measure S11 at cable end → should see open circuit (S11 ≈ 0 dB at 0°) → if not, cable or connector problem
- Connect precision 50 Ω load: should read S11 < −35 dB → confirms VNA calibration
- Reconnect antenna: find resonance frequency (deepest S11 dip)
- Smith chart: Is resonance in right place? Is impedance inductive or capacitive?
- Design matching network: RF View Auto Match from measured S11
Quick Field VSWR Diagnosis
No VNA available? Use a directional coupler + power meter: Forward power: 10 W Reflected power: 1.11 W |Γ| = √(P_reflected/P_forward) = √(1.11/10) = 0.333 VSWR = (1+0.333)/(1−0.333) = 2.0:1 Return Loss = −20·log(0.333) = 9.5 dB
RF View VSWR Diagnosis: After measuring with a VNA, load the .s1p file into RF View. VSWR view shows the frequency profile. Auto Match designs a fix. Free on Android.