VSWR

VSWR = (1 + |Γ|) / (1 − |Γ|)

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Formula

VSWR = (1 + |Γ|) / (1 − |Γ|)

Description

Voltage Standing Wave Ratio measures the impedance mismatch between a transmission line and its load. A perfect match gives VSWR = 1:1 (Γ = 0), meaning all power is absorbed by the load. Higher VSWR values indicate worse matching with more power reflected back to the source. VSWR of 2:1 means about 11% of power is reflected, while 3:1 reflects 25%. Excessive VSWR can damage transmitter amplifiers due to reflected power and creates standing waves that cause voltage peaks along the transmission line.

Variables

  • VSWR — Voltage Standing Wave Ratio (dimensionless, ≥1)
  • |Γ| — Magnitude of reflection coefficient (0 to 1)

Practical Notes

VSWR targets: antenna systems <1.5:1, general RF <2:1, broadband acceptable <3:1. A VSWR of 1.5:1 corresponds to return loss of 14 dB and 4% reflected power. Network analyzers measure VSWR directly. In practice, achieving VSWR < 1.2:1 over a wide bandwidth requires careful impedance matching using stubs, transformers, or matching networks.

Related Concepts

All Signal & RF formulas →
Wavelength Free Space Path Loss Signal-to-Noise Ratio Nyquist Sampling Rate Link Budget Antenna Gain Skin Depth Friis Noise Figure (3-stage)

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