Impedance Mismatch Loss Calculator (with Examples)

This tool uses the impedance of the source and load to calculate the impedance mismatch. It also calculates

  • Reflection Coefficient
  • VSWR (Voltage Standing Wave Ratio)
  • Return loss
  • Mismatch loss
  • Forward power
  • Reflected power

Formula

Source Impedance = Z0

Complex Load Impedance = R + j*X

Absolute Load Impedance = √(R2 + X2)

Γ = √[(R-Z0)2 + X2] / √[(R+Z0)2 + X2]

Mismatch Loss (dB) = -10*Log10(1 – |Γ|2)

Return Loss (dB) = -20*Log10(|Γ|)

Reflected Power (%) = 100*(|Γ|2)

Transmitted Power (%) = 100*(1 – |Γ|2)

Example Calculations

Complex Load

For a source impedance of 50 ohm and complex load impedance of 25 + j*25, the return loss is 7 dB and 20% of the power is reflected back with the balance of 80% transferred forward.

If the source and the load are perfectly matched, the VSWR is 1 and 100% of the power is transferred.

50 ohm – 75 ohm mismatch loss

A question that comes up often in the context of using an amplifier or filter designed for 75 ohm in a 50 ohm system. In this case, what’s the mismatch loss?

When you use those numbers in the calculator above for the load Impedance = R + j*X with R= 75, X = 0

The mismatch loss is calculated to be 0.18 dB. As a result of this mismatch, only 4% of the incident power is reflected back, while 96% is transmitted forward.

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