liminfoVSWR Calculator
Free web tool: VSWR Calculator
VSWR
2.000
Γ (Reflection)
0.3333
Return Loss
9.54 dB
Mismatch Loss
0.512 dB
About VSWR Calculator
The VSWR Calculator converts between five different representations of RF impedance mismatch: VSWR (Voltage Standing Wave Ratio), reflection coefficient Γ (gamma), return loss in dB, mismatch loss in dB, and load impedance relative to the reference impedance Z0. Select the input mode that matches the value you have — for example, a VSWR measured on a VNA, a return loss spec from a datasheet, or the load and source impedances from a circuit schematic — and the tool instantly displays all four output metrics, with each derivation correct to four significant figures.
RF engineers, antenna designers, and ham radio operators use VSWR as a measure of how well a transmission line is terminated. A perfect match gives VSWR = 1.000 (Γ = 0, return loss = ∞ dB). In practice, a VSWR below 1.5 (return loss > 14 dB) is considered good for most antenna and transmission-line systems. The reflection coefficient Γ = (ZL − Z0) / (ZL + Z0) is the fundamental quantity from which all other metrics are derived. Return loss (RL) = −20 × log10(Γ) measures the fraction of power reflected back from the load. Mismatch loss (ML) = −10 × log10(1 − Γ²) measures the fraction of incident power that is lost due to the mismatch and does not reach the load.
Five input modes are supported: enter a known VSWR (≥1), a return loss value in dB (positive means power is reflected, higher is better), a reflection coefficient between 0 and 1, a mismatch loss in dB, or the load impedance ZL and characteristic impedance Z0 separately. All conversions run entirely in your browser — no data is sent to any server — making it safe to use with proprietary circuit designs and test data.
Key Features
- Five input modes: VSWR, return loss (dB), reflection coefficient Γ, mismatch loss (dB), and ZL/Z0 impedance
- Calculates all four RF mismatch metrics simultaneously from a single input
- Z-mode accepts load impedance and characteristic impedance (Z0) as separate inputs
- Results displayed to three or four significant figures with appropriate units
- Handles edge cases: clamps Γ to [0, 0.9999] to prevent division-by-zero for VSWR
- Covers the full practical range from near-perfect match to severe mismatch
- 100% client-side processing — no data uploaded to any server
- Compact, tab-based interface for fast switching between input types on any device
Frequently Asked Questions
What is VSWR?
VSWR (Voltage Standing Wave Ratio) is the ratio of the maximum to minimum voltage amplitude of the standing wave pattern on a transmission line caused by the superposition of the incident and reflected waves. A VSWR of 1.0 means a perfect match with no reflection. A VSWR of 2.0 means 1/9 (≈11%) of incident power is reflected. VSWR = (1 + Γ) / (1 − Γ).
What is return loss?
Return loss (RL) is the ratio of incident power to reflected power, expressed in dB: RL = −20 × log10(Γ). A higher return loss means less power is reflected. RL = 0 dB means all power is reflected (Γ = 1, open or short circuit). RL = 20 dB means 1% of power is reflected (Γ = 0.1, VSWR ≈ 1.22).
What is the reflection coefficient Γ?
The reflection coefficient Γ (gamma) is the ratio of the reflected voltage wave amplitude to the incident voltage wave amplitude. It ranges from 0 (perfect match) to 1 (total reflection). For a resistive load: Γ = (ZL − Z0) / (ZL + Z0), where ZL is the load impedance and Z0 is the characteristic impedance of the transmission line.
What is mismatch loss?
Mismatch loss (ML) is the power lost due to impedance mismatch — the portion of incident power that is neither delivered to the load nor reflected, but lost as heat in the connector or transmission line. ML = −10 × log10(1 − Γ²). For a VSWR of 2.0, mismatch loss is approximately 0.51 dB.
What is a good VSWR value?
For most antenna and RF systems, a VSWR below 2.0 (return loss > 9.5 dB) is acceptable, and below 1.5 (return loss > 14 dB) is considered good. Connectors and cables typically specify VSWR < 1.1 (return loss > 26 dB). Critical systems like satellite communication may require VSWR < 1.2.
What is the characteristic impedance Z0?
Z0 is the impedance of the transmission line itself — for coaxial cable in RF systems, this is typically 50 Ω (for instrumentation and telecommunications) or 75 Ω (for cable TV and video). Z0 is set by the geometry and dielectric of the cable and is independent of the load.
How do I convert a VNA S11 measurement to VSWR?
S11 (in dB) is the same as return loss with a sign convention: S11 = −RL in dB for a passive load. To convert: Γ = 10^(S11/20), then VSWR = (1 + Γ) / (1 − Γ). Enter the S11 magnitude (as a positive return loss value) in the Return Loss mode of this calculator.
Can I use this for impedance matching network design?
Yes. Use the Z-mode to enter your load impedance ZL and your system Z0. The tool tells you the current mismatch (VSWR, Γ, RL, ML). Once you design a matching network (L-network, pi-network, transformer) that transforms ZL to Z0, re-enter the new effective impedance to verify that the mismatch metrics meet your specification.