S11 to Impedance Calculator

Use this tool to calculate the load impedance from S11, the input reflection coefficient.


  • Zo – source characteristic impedance in Ω
  • S11 – either linear or dB value can be used

The tool will calculate the absolute value of the load impedance ZL in ohm.


S11 is the input reflection coefficient with a value between 0 and 1. (Entering values outside this range will result in meaningless output). Referring to the picture of a two port network shown below, S11 = b1/a1

If the load impedance is not the same as the characteristic impedance, there will be some reflection. In actual practice, this reflected signal is measured with a network analyzer.


VSWR = (1+|S11|)/(1-|S11|)

Γ = (VSWR – 1)/(VSWR + 1)

ZL = Zo*(1+Γ)/(1-Γ)

Example Calculations

For a source impedance of 50 Ω and S11 = -20 dB, the load impedance is calculated to be 61 Ω.

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