Return Loss Calculator Formula

Understand the math behind the return loss calculator. Each variable explained with a worked example.

Use the Return Loss Calculator

Formulas Used

Return Loss

return_loss_db = -20 * log10(gamma_from_vswr)

Reflection Coefficient

refl_coeff = gamma_from_vswr

Power Reflected

power_refl_pct = pow(gamma_from_vswr, 2) * 100

Power Delivered

power_delivered_pct = (1 - pow(gamma_from_vswr, 2)) * 100

Mismatch Loss

mismatch_loss_db = -10 * log10(1 - pow(gamma_from_vswr, 2))

Variables

VariableDescriptionDefault
vswr_inVSWR1.8
gamma_from_vswrDerived value= (vswr_in - 1) / (vswr_in + 1)calculated

How It Works

Understanding Return Loss

Return loss measures how much signal is reflected due to impedance mismatch, expressed in positive decibels (higher is better).

Formulas

Gamma = (VSWR - 1) / (VSWR + 1)

Return Loss = -20 x log10(Gamma) dB

Mismatch Loss = -10 x log10(1 - Gamma^2) dB

Quick Reference

  • 20 dB return loss: 1% power reflected, VSWR 1.22
  • 14 dB return loss: 4% power reflected, VSWR 1.50
  • 10 dB return loss: 10% power reflected, VSWR 1.92

    • Worked Example

    A cable assembly has VSWR 1.8:1.

    vswr_in = 1.8
    1. 01Gamma = (1.8 - 1) / (1.8 + 1) = 0.8 / 2.8 = 0.2857
    2. 02Return loss: -20 x log10(0.2857) = 10.88 dB
    3. 03Power reflected: 0.2857^2 x 100 = 8.16%
    4. 04Power delivered: 91.84%
    5. 05Mismatch loss: -10 x log10(0.9184) = 0.370 dB

    Ready to run the numbers?

    Open Return Loss Calculator