Readers of my articles occasionally ask for explanation of the distinction between meanings of:

- Insertion Loss;
- Mismatch Loss;
- Loss (or Transmission Loss).

These terms apply to linear circuits, it circuits that comply with linear circuit theory, things like that impedances are independent of voltage and current, sources are well represented by Thevenin and Norton equivalent circuits.

### Insertion Loss

Insertion Loss is the ratio of power into a matched load (to mean that the load impedance is the complex conjugate of the Thevenin equivalent source impedance) to the power in the load with the subject network / device inserted.

Insertion Loss can also be expressed in dB.

### Mismatch Loss

Mismatch Loss is the ratio of output power of a source into a matched load to the output power under a given mismatch.

Mismatch Loss can also be expressed in dB.

### Loss

Loss is simply \(\frac{Power_{in}}{Power_{out}}\).

Loss can also be expressed in dB.

Loss is sometimes called Transmission Loss to distinguish it from other qualifications, but it is unnecessary. Recent hammy Sammy practice is to label |s21| graphs Transmission Loss which is an error on two counts.

Let’s illustrate these with some examples using Simsmith. Whilst these are models, you would expect to measure similar results using a good VNA or like test equipment. Continue reading On Insertion Loss