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.
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.