Mismatch Loss
Understanding Mismatch Loss
Mismatch loss is the power that is reflected back from a load due to impedance mismatch and therefore never delivered. It is fundamentally different from dissipative (insertion) loss: mismatch loss returns power to the source while insertion loss converts power to heat.
Mismatch Loss Values
| VSWR | |Gamma| | RL (dB) | ML (dB) | % Reflected |
|---|---|---|---|---|
| 1.0:1 | 0 | Inf | 0 | 0% |
| 1.2:1 | 0.091 | 20.8 | 0.036 | 0.8% |
| 1.5:1 | 0.200 | 14.0 | 0.177 | 4.0% |
| 2.0:1 | 0.333 | 9.5 | 0.512 | 11.1% |
| 3.0:1 | 0.500 | 6.0 | 1.25 | 25% |
ML = -10 log10(1 - |Gamma|^2) dB
Or from VSWR:
ML = -10 log10(1 - ((VSWR-1)/(VSWR+1))^2) dB
Or from return loss:
ML = -10 log10(1 - 10^(-RL/10)) dB
Frequently Asked Questions
What is mismatch loss?
Mismatch loss is power lost due to impedance mismatch, caused by reflection. ML = -10 log(1-|Gamma|^2) dB. At VSWR 2:1, 11% of power is reflected (0.51 dB loss). It is in addition to any insertion (dissipative) loss.
Is mismatch loss the same as insertion loss?
No. Mismatch loss is power reflected back toward the source (not delivered). Insertion loss is power absorbed and converted to heat inside the component. Total loss = insertion loss + mismatch loss. For well-matched components, mismatch loss is small.
When does mismatch loss matter?
Mismatch loss matters when system efficiency is critical (transmitter output, satellite links, phased array feeds). At VSWR 1.5:1 (return loss 14 dB), only 0.18 dB is lost to mismatch. At VSWR 3:1, 1.25 dB is lost, which can be significant.