VSWR and Return Loss Calculator (Antenna and Cable Mismatch)
VSWR, reflection coefficient, return loss, mismatch loss and the power reflected back, from the line impedance and the load you actually have.
Results
The dashed line marks the value you entered.
What this tool does
A load that differs from the line impedance reflects part of the wave: the reflection coefficient Γ = (Z_L − Z₀) ÷ (Z_L + Z₀) is a complex number, and VSWR is just a way of writing its size. A 75 Ω load on a 50 Ω line gives Γ = 0.2, VSWR 1.5 and a return loss of 14 dB, yet only 4 % of the power is reflected and the loss is under 0.2 dB, which is why a VSWR of 1.5 is not worth worrying about. The numbers here describe the load itself; the loss in a long, lossy cable makes the VSWR seen at the radio look better than it is.
Formula
Γ = (Z_L − Z₀) ÷ (Z_L + Z₀) · VSWR = (1 + |Γ|) ÷ (1 − |Γ|) · return loss = −20 log₁₀|Γ| · mismatch loss = −10 log₁₀(1 − |Γ|²)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
z0 | Characteristic impedance of the line | Ω |
rl | Load resistance (real part) | Ω |
xl | Load reactance (imaginary part, positive if inductive) | Ω |
pf | Forward power from the transmitter | W |
VS | VSWR | — |
GM | Reflection coefficient |Γ| | — |
RLD | Return loss | dB |
ML | Mismatch loss | dB |
PR | Power reflected back | W |
PD | Power delivered to the load | W |
Worked example
- Characteristic impedance of the line50 Ω
- Load resistance (real part)75 Ω
- Load reactance (imaginary part, positive if inductive)0 Ω
- Forward power from the transmitter100 W
- VSWR1.500
- Reflection coefficient |Γ|0.2000
- Return loss13.98 dB
- Mismatch loss0.177 dB
- Power reflected back4.00 W
- Power delivered to the load96.00 W
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.