VSWR, Return Loss & Reflected Power Calculator

How it works

|Γ| = √(P_ref ÷ P_fwd) = (VSWR − 1) ÷ (VSWR + 1) = 10^(−RL/20) = |(Z_L − Z₀) ÷ (Z_L + Z₀)|; VSWR = (1 + |Γ|) ÷ (1 − |Γ|); RL = −20 log|Γ|; reflected fraction = |Γ|²; mismatch loss = −10 log(1 − |Γ|²)

When an antenna or load does not present the impedance the transmission line expects, part of the wave reflects back toward the source. The reflection coefficient is the ratio of reflected to forward voltage; VSWR expresses the same thing as the ratio of the standing-wave maxima to minima on the line, and return loss as decibels of reflected power below the forward power — three languages for one number, which this tool converts among. A VSWR of 1.5:1 sounds alarming but reflects only 4% of the power (0.18 dB), so mismatch loss is rarely the real problem; what matters is that reflected power stresses solid-state transmitter finals, which fold back power above about 2:1, and that a rising VSWR is the first sign of water in a connector or a detuned antenna. In a low-loss feedline the reflected power is largely re-reflected and radiated, so the true loss is the extra attenuation from multiple trips, not the reflected fraction itself.

Worked example

A wattmeter reads 100 W forward and 4 W reflected: |Γ| = 0.2, VSWR 1.50:1, return loss 14.0 dB; 4% of the power is reflected, a mismatch loss of just 0.18 dB with 96 W delivered — equivalent to a 33 Ω or 75 Ω resistive load in a 50 Ω system. Acceptable for almost any transmitter.

Frequently asked questions