Mismatch loss

Mismatch loss represents the amount of power wasted in the system[dubious – discuss].

It can also be thought of as the amount of power gained if the system was perfectly matched[dubious – discuss].

Impedance matching is an important part of RF system design; however, in practice there will likely be some degree of mismatch loss.

According to Walter Maxwell[2] mismatch does not result in any loss ("wasted" signal), except through the transmission line.

Note that as the reflection coefficient approaches zero, power to the load is maximized.

In terms of the voltage standing wave ratio (VSWR): [3] Any component of the transmission line that has an input and output will contribute to the overall mismatch loss of the system.

Likewise, a large amount of the loss in amplifiers comes from the mismatch between the input and output.

Other common RF system components such as filters, attenuators, splitters, and combiners will generate some amount of mismatch loss.

Figure 1. Simple circuit showing characteristic impedance Z o and the load impedance Z L . In a perfectly matched system Z L =Z o , and there is no mismatch loss.
Figure 2. Simple circuit showing incident power, P i , on a load. The reflected power will be the difference between P i and the power delivered, P d .
Figure 3. Simple circuit showing multiple reflections due to more than 1 mismatched device.