The basics
Return loss and VSWR both describe how well a component is matched to the system impedance. Better matching means less reflected power and more efficient transfer.
Definitions
- Return loss — the ratio, in dB, of reflected to incident power. Higher is better. It is simply S11 expressed as a positive dB value; see S-parameters for the full picture.
- VSWR — the ratio of maximum to minimum voltage on the line. 1.0:1 is perfect.
- Reflection coefficient — the amplitude ratio of reflected to incident wave.
Useful conversions
- A return loss of 20 dB corresponds to about 1.22:1 VSWR.
- A return loss of 14 dB corresponds to about 1.5:1 VSWR.
- A return loss of 10 dB corresponds to about 1.92:1 VSWR.
Why it matters
- Reflections cause ripple and reduce delivered power.
- Poor match can stress or destabilize amplifiers.
- Most systems target 15 dB return loss or better, achieved with matched terminations on unused ports.
Practical tip
Measure return loss with a calibrated vector network analyzer and verify it across the full operating band, not just at center frequency.