VSWR Calculator — Voltage Standing Wave Ratio

VSWR reference table

Common VSWR values with their derived metrics (computed with the same formulas as the calculator above):

VSWR quality guide

Frequently asked questions (FAQ)

What is VSWR (voltage standing wave ratio)?

VSWR is a measure of how well a load impedance (e.g. an antenna) matches the transmission line impedance. A VSWR of 1.0 : 1 means a perfect match — no power is reflected. The larger the VSWR, the more power is reflected back to the source.

What is the VSWR formula from the reflection coefficient?

VSWR = (1 + |Γ|) / (1 − |Γ|), where |Γ| is the magnitude of the reflection coefficient (0 to < 1). Example: |Γ| = 0.2 → VSWR = 1.2 / 0.8 = 1.5 : 1.

What does a VSWR of 1.5 mean?

A VSWR of 1.5 : 1 means |Γ| = 0.2 — 4 % of power is reflected, return loss 13.9794 dB, and mismatch loss 0.1773 dB. This is generally considered excellent for antenna installations.

What does a VSWR of 2.0 mean?

A VSWR of 2.0 : 1 means |Γ| = ⅓ — 11.1111 % of power is reflected back, return loss 9.5424 dB, and mismatch loss 0.5115 dB. Still acceptable for many applications, but already at the edge of "good".

What is the difference between VSWR, return loss, and mismatch loss?

All three describe the same impedance mismatch from different angles: VSWR is a ratio (e.g. 2.0 : 1), return loss is |Γ| in dB using 20·log (e.g. 9.5424 dB), while mismatch loss is the power lost to reflection in dB using 10·log (e.g. 0.5115 dB).

Why does return loss use 20·log while mismatch loss uses 10·log?

Because return loss is derived from a voltage/wave ratio (|Γ| is a field quantity), so it uses 20·log₁₀. Mismatch loss is derived from a power ratio (1 − |Γ|²), so it uses 10·log₁₀.

What is the ideal VSWR?

The ideal VSWR is 1.0 : 1 (perfect match, 0 dB mismatch loss). In practice, VSWR ≤ 1.5 is excellent, ≤ 2.0 good, up to 3.0 still fair, and above 3.0 the installation should be checked.

How do I calculate |Γ| from forward and reflected power?

|Γ| = √(Pr / Pf). Example: 100 W forward power and 4 W reflected power → |Γ| = √0.04 = 0.2 → VSWR = 1.5 : 1.

How do I convert return loss to VSWR?

Reverse the formula: |Γ| = 10^(−RL/20), then VSWR = (1 + |Γ|) / (1 − |Γ|). Example: RL 9.5424 dB → |Γ| = ⅓ → VSWR = 2.0 : 1.

What is mismatch loss?

Mismatch loss is the power (in dB) lost because some power is reflected due to impedance mismatch: ML = −10·log₁₀(1 − |Γ|²). Example: at VSWR 2.0, mismatch loss = 0.5115 dB.