Calculate VSWR, return loss, reflection coefficient, and mismatch loss. Input from VSWR, impedance, or return loss. Power distribution visual and comprehensive reference table.
The Voltage Standing Wave Ratio (VSWR) quantifies impedance mismatch on a transmission line. When a load impedance (ZL) differs from the line's characteristic impedance (Z₀), part of the signal reflects back, creating standing waves. VSWR ranges from 1:1 (perfect match, no reflection) to infinity (total reflection, open or short circuit). A VSWR of 2:1 means 11% of power is reflected.
VSWR is directly related to the reflection coefficient Γ = (ZL − Z₀)/(ZL + Z₀) by the formula VSWR = (1 + |Γ|)/(1 − |Γ|). It is also connected to return loss (RL = −20log|Γ| dB) and mismatch loss (ML = −10log(1 − |Γ|²) dB). These parameters fully describe how well a load is matched and how much power is lost to reflections.
This calculator converts between VSWR, reflection coefficient, return loss, and impedance mismatch. Enter from any direction (VSWR value, impedance pair, or return loss) and get all related parameters plus a power distribution breakdown for any forward power level. A comprehensive reference table provides quick lookup for common VSWR values.
VSWR, return loss, reflection coefficient, and mismatch loss are all different ways to express the same physical phenomenon — impedance mismatch. Converting between them requires logarithms and careful algebra. This calculator handles all conversions instantly and provides a power distribution visual so you can see exactly how much power reaches the load.
Reflection Coefficient: Γ = (Z_L − Z₀) / (Z_L + Z₀) VSWR: VSWR = (1 + |Γ|) / (1 − |Γ|) Return Loss: RL = −20 × log₁₀(|Γ|) dB Mismatch Loss: ML = −10 × log₁₀(1 − |Γ|²) dB Reflected Power: P_r = |Γ|² × P_forward Delivered Power: P_load = P_forward − P_reflected P_load = P_forward × (1 − |Γ|²)
Result: Γ = 0.333, RL = 9.54 dB, reflected = 11.1 W, delivered = 88.9 W
A VSWR of 2:1 gives Γ = (2−1)/(2+1) = 0.333. Return loss = −20log(0.333) = 9.54 dB. Reflected power = 0.333² × 100 = 11.1 W. Delivered power = 88.9 W (88.9% efficiency). This is generally considered acceptable for most amateur radio and communications applications.
When forward and reflected waves superpose on a transmission line, they create a standing wave pattern. Voltage maxima occur where forward and reflected waves add constructively (separated by half-wavelength intervals), and minima occur where they cancel. The ratio of maximum to minimum voltage is the VSWR. At VSWR = 1:1, the voltage is uniform along the line; at any higher VSWR, the voltage oscillates spatially.
The Smith Chart is a graphical tool that maps complex impedance to reflection coefficient on a unit circle. VSWR appears as circles centered on the chart origin — a VSWR of 2:1 is a circle of radius 0.333. Engineers use the Smith Chart to design matching networks (L-networks, pi-networks, stub tuners) that transform the load impedance to the line impedance, reducing VSWR to near 1:1.
VSWR is measured using directional couplers, SWR bridges, or network analyzers. Directional couplers sample forward and reflected power separately, from which Γ and VSWR are calculated. Vector network analyzers (VNA) measure both magnitude and phase of Γ across frequency, providing complete impedance characterization. Modern handheld VNAs make field VSWR measurement accessible to any technician.
For amateur radio: below 2:1. For commercial/cellular: below 1.5:1. For precision lab equipment: below 1.1:1. Most modern transmitters can handle up to 3:1 before reducing power or shutting down.
Impedance mismatch between the transmission line and the load. Common causes: antenna not resonant at the operating frequency, wrong cable impedance (50Ω vs 75Ω), damaged connectors, water in the cable, or incorrect antenna length.
Perfect match (VSWR = 1.0:1) is theoretically possible but practically unachievable across a bandwidth. A well-tuned antenna at a single frequency can approach 1.05:1, but over any bandwidth, some mismatch is inevitable.
The VSWR at the load does not change. However, the VSWR measured at the transmitter end can appear lower because cable loss attenuates the reflected signal. This is why VSWR should ideally be measured at the antenna feedpoint.
Antennas typically have a VSWR bandwidth — the frequency range where VSWR stays below a threshold (usually 2:1). Narrow-band antennas have tight VSWR curves; broadband antennas maintain low VSWR over wide ranges.
Yes, high reflected power can damage the output stage of a transmitter. Most modern transmitters have SWR protection that reduces power or shuts down above 3:1. Older tube transmitters are more tolerant but can still be damaged by severe mismatch.