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VSWR & Return Loss Calculator

Calculate the relationship between VSWR, Return Loss (dB), and Reflection Coefficient (Γ). Enter any one value to automatically compute the other two.

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dB

Mathematical Relationships

From Reflection Coefficient (Γ)

  • VSWR = (1 + |Γ|) / (1 - |Γ|)
  • RL (dB) = -20 * log10(|Γ|)

From VSWR

  • |Γ| = (VSWR - 1) / (VSWR + 1)
  • RL (dB) = -20 * log10( (VSWR - 1) / (VSWR + 1) )

From Return Loss (RL)

  • |Γ| = 10^(-RL / 20)
  • VSWR = (1 + |Γ|) / (1 - |Γ|)

Engineering Background

Voltage Standing Wave Ratio (VSWR) measures the degree of impedance matching and reflection between an RF transmission line and a load (such as an antenna). A perfect impedance match means a VSWR of 1.0:1, indicating no energy is reflected.

Return Loss is another way of expressing mismatch. It is a logarithmic ratio measured in dB that compares the power reflected by the antenna to the power that is fed into the antenna from the transmission line. A higher return loss (e.g., >20 dB) means less power is reflected back and the match is better.

Reflection Coefficient (|Γ|) is strictly defined as the ratio of reflected voltage to incident voltage. It ranges theoretically from 0 to 1, where |Γ| = 0 represents a perfect match, and |Γ| = 1 indicates 100% total reflection.

Meaning of VSWR Values

VSWR is usually expressed as a ratio (e.g., 1.5:1, often shortened to 1.5). The table below illustrates the practical implications of different VSWR values:

VSWR Reflected Power Match Status Practical Impact
1.0 : 1 0% Perfect Match Ideal state, all energy transmitted, extremely hard to achieve in reality.
1.1 - 1.3 : 1 < 2% Excellent Excellent state in practical engineering, negligible loss.
1.5 : 1 4% Good Standard requirement for amateur radio and most communication systems.
2.0 : 1 11.1% Critical Point Noticeable power waste begins, some sensitive equipment may trigger protection.
3.0 : 1 or higher > 25% Severe Mismatch Severe energy reflection, radio equipment may overheat significantly.
∞ (Infinity) 100% Total Reflection Antenna open or short circuit, 100% energy reflected.

How is Reflected Power calculated?

Step 1: Calculate the reflection coefficient from VSWR: |Γ| = (VSWR - 1) / (VSWR + 1).
Step 2: Since power is proportional to the square of voltage, the reflected power percentage is simply the square of the reflection coefficient: Reflected Power % = |Γ|² × 100%.
For example, if VSWR is 1.5, |Γ| = 0.2. Squaring that gives 0.04, which means 4% of the incident power is reflected.

Calculator quality evidence

Purpose of this calculator

Use this tool to translate a scalar mismatch measurement between VSWR, reflection coefficient magnitude, and return loss while checking whether the value is physically admissible.

Formula and variables

|Γ| = (VSWR−1)/(VSWR+1); return loss RL = −20·log10(|Γ|); VSWR = (1+|Γ|)/(1−|Γ|). Mismatch loss is a separate power metric, not another name for return loss.

Physical assumptions and scope

The scalar relation assumes a defined reference impedance and a passive one-port mismatch with 0 ≤ |Γ| < 1 for finite VSWR. VSWR 1 gives Γ = 0 and an ideal infinite return loss; real instruments have a finite floor.

Valid input scope

VSWR must be at least 1, return loss must be non-negative, and reflection coefficient magnitude must lie from 0 to 1. Invalid values stay visible as feedback instead of producing a fabricated result.

Independently checked test vectors

  1. 2 VSWR → 9.542 return loss (dB)(forward)
  2. 9.542 return loss (dB) → 2 VSWR(reverse)

Conversion-specific misuse to avoid

Do not infer a complete antenna or cable diagnosis from one scalar value: frequency dependence, phase, connector repeatability, and calibration still matter. Do not enter a dB loss with the sign of insertion loss and call it return loss.

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