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SWR / Reflected Power Calculator

Calculate reflected power from forward power and SWR, or work backwards from forward and reflected power to determine SWR. The tool also shows delivered power, reflection coefficient and return loss.

Calculate

Power travelling from the transmitter toward the load or antenna.
Enter the voltage standing-wave ratio. Minimum valid value is 1.00:1.
Useful relationships RF mismatch
Reflection coefficient magnitude:
|Γ| = (SWR − 1) / (SWR + 1)

Reflected power fraction:
Pr / Pf = |Γ|²
Forward and reflected RF power Live diagram

Enter forward power to visualise power travelling toward the antenna and the portion reflected back by the mismatch.

How the calculation works

SWR is related to the magnitude of the voltage reflection coefficient Γ. A perfect match has Γ = 0 and SWR = 1:1.

|Γ| = (SWR − 1) / (SWR + 1)
SWR = (1 + |Γ|) / (1 − |Γ|)

The fraction of forward power that is reflected is the square of the reflection-coefficient magnitude:

Preflected / Pforward = |Γ|²

The power accepted by the load at that measurement point is therefore:

Pdelivered = Pforward − Preflected

Return loss expresses the same mismatch logarithmically:

Return loss (dB) = −20 × log10(|Γ|)

Worked example

Enter values above to see the calculation worked through here.

Some useful SWR landmarks

An SWR of 1.5:1 reflects about 4% of the forward power. 2:1 reflects about 11.1%. 3:1 reflects 25%. The percentage of reflected power therefore rises much faster than the SWR number itself may suggest.

Reflected power is not automatically transmitter loss

The reflected wave travels back toward the source and may be re-reflected or absorbed depending on the transmitter, tuner, feedline loss and the rest of the RF system. This calculator simply describes the forward/reflected relationship at the chosen measurement point.

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