Insertion loss

Insertion loss is a figure of merit for an electronic filter and this data is generally specified with a filter. Insertion loss is defined as a ratio of the signal level in a test configuration without the filter installed (|V₁|) to the signal level with the filter installed (|V₂|). This ratio is described in dB by the following equation:

${\displaystyle {\mbox{Insertion loss (dB)}}=10\log _{10}{\left|V_{1}\right|^{2} \over \left|V_{2}\right|^{2}}=20\log _{10}{\left|V_{1}\right| \over \left|V_{2}\right|}}$

For passive filters, |V₂| will be smaller than |V₁|. In this case, the insertion loss is positive and measures how much smaller the signal is after adding the filter.

In case the two measurement ports use the same reference impedance, the insertion loss (${\displaystyle IL}$) is defined as:[1][2]

${\displaystyle IL=-20\log _{10}\left|S_{21}\right|\,{\text{dB}}}$.

Here ${\displaystyle S_{21}}$ is one of the scattering parameters. Insertion loss is the extra loss produced by the introduction of the DUT between the 2 reference planes of the measurement. The extra loss can be introduced by intrinsic loss in the DUT and/or mismatch. In case of extra loss the insertion loss is defined to be positive.

• Mismatch loss
• Return loss

•  This article incorporates public domain material from the General Services Administration document: "Federal Standard 1037C".