This calculator determines the Voltage Standing Wave Ratio (VSWR) from the measured forward and reflected power in an RF transmission line. VSWR is a measure of how efficiently power is transmitted from a source to a load, with a value of 1 indicating perfect matching (no reflection).
Formula
VSWR = (1 + √(Pr / Pf)) / (1 – √(Pr / Pf))
Formula Explanation
- Pf = Forward Power (Watts)
- Pr = Reflected Power (Watts)
- VSWR = Voltage Standing Wave Ratio (unitless)
Usage Notes
- Ensure Pf > Pr; otherwise, VSWR will be invalid.
- VSWR indicates reflection: lower values mean better matching between load and source.
- Used for antenna testing, transmission line diagnostics, and RF system tuning.
Example Calculation
Input: Pf = 100 W, Pr = 11.1 W
Output:
- √(Pr / Pf) = √(11.1 / 100) = 0.333
- VSWR = (1 + 0.333) / (1 – 0.333) = 1.333 / 0.667 = 2.0
A reflected power of 11.1 W with 100 W forward power corresponds to a VSWR of 2.0.