Return Loss

Formula

Description

Return loss quantifies how well a load is matched to a transmission line, expressed as a positive dB value. Higher return loss means better matching (less reflection). It is the negative of the reflection coefficient expressed in dB. Return loss is the most common metric displayed on network analyzers (as S11 magnitude) and is used to characterize antennas, connectors, cables, and any RF component. A return loss of 10 dB means 10% of the incident power is reflected, while 20 dB means only 1% is reflected.

Variables

• RL — Return loss in positive decibels (dB)
• |Γ| — Magnitude of reflection coefficient (0 to 1)

Practical Notes

Good match: RL > 20 dB. Acceptable: RL > 10 dB. Poor: RL < 6 dB. S11 on a network analyzer is return loss with a negative sign. Return loss and VSWR are related: RL = 20×log10((VSWR+1)/(VSWR-1)). For differential pairs (USB, PCIe), both single-ended (SDD11) and differential return loss are specified.