VSWR Calculator
Convert between VSWR, return loss, reflection coefficient and mismatch loss, or compute VSWR directly from a load impedance.
What VSWR is
VSWR (Voltage Standing Wave Ratio) quantifies how much of the RF power sent toward an antenna is reflected back due to an impedance mismatch, instead of being radiated. VSWR 1.0 means a perfect match and zero reflection; higher ratios mean more reflected power and, on a real transmitter, more risk of power amplifier stress.
VSWR, return loss and reflection coefficient
These three numbers describe the same physical mismatch in different units. Reflection coefficient magnitude |G| is the fraction of voltage reflected. VSWR is (1 + |G|) / (1 - |G|). Return loss in dB is -20 × log10(|G|), note it moves in the opposite direction: a better match means higher return loss but lower VSWR.
VSWR from load impedance
For a purely resistive load Zload on a line of characteristic impedance Z0 (typically 50 ohm in cellular RF): |G| = |Zload - Z0| / (Zload + Z0). This calculator's load-impedance mode covers the resistive case; a complex impedance with reactance needs a full Smith chart calculation.
Reading a VSWR value
VSWR under 1.5 is a good match for many cellular sites, while acceptance limits depend on the operator, antenna and equipment specification. A high reading during a site sweep may indicate a damaged connector, feeder or antenna and should be correlated with sweep setup and physical inspection.
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Frequently Asked Questions
What is VSWR?
VSWR (Voltage Standing Wave Ratio) measures how well an antenna or load impedance is matched to the characteristic impedance of the feedline (usually 50 ohms). A perfect match gives VSWR 1.0, higher values mean more of the transmitted power is reflected back toward the source instead of radiated.
What VSWR is considered good?
As a general rule of thumb, VSWR below 1.5 is considered a good match for most cellular installations, and below 2.0 is usually acceptable. Above that, reflected power loss and risk of PA damage increase. Always check the specific equipment manufacturer tolerance.
What is return loss?
Return loss is the same mismatch expressed in dB instead of a ratio: RL(dB) = -20 x log10(reflection coefficient). Higher return loss (in dB) means a better match, the opposite direction from VSWR.
How do I convert VSWR to return loss?
First compute the reflection coefficient magnitude from VSWR: |G| = (VSWR - 1) / (VSWR + 1), then return loss = -20 x log10(|G|). This calculator does both steps automatically.
What causes high VSWR in the field?
Common causes include damaged or water-ingressed connectors, a cracked or kinked feeder cable, a faulty antenna, or an impedance mismatch from incorrect cable length or connector type. High VSWR is usually diagnosed with a site sweep test before troubleshooting further.
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