Editing Insertion loss

{{Short description|Loss of signal transmission power when devices are connected to a transmission line}}
{{Use American English|date = March 2019}}

In [[telecommunications]], '''insertion loss''' is the loss of [[signal]] [[power (physics)|power]] resulting from the insertion of a device in a [[transmission line]] or [[optical fiber]] and is usually expressed in [[decibel]]s (dB).  

If the power transmitted to the load before insertion is ''P''<sub>T</sub> and the power received by the load after insertion is ''P''<sub>R</sub>, then the insertion loss in decibels is given by,

:<math>IL(\mathrm{dB}) = 10 \log_{10} {P_\mathrm T \over P_\mathrm R}</math>

==Electronic filters==

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 (<math>\left\vert V_1 \right\vert</math>) to the signal level with the filter installed  (<math>\left\vert V_2 \right\vert</math>).  This ratio is described in decibels by the following equation:

:<math>\mbox{Insertion loss (dB)} = 10 \log_{10} {\frac{ \left\vert V_1 \right\vert ^2 }{ \left\vert V_2 \right\vert ^2 }} = 20 \log_{10} { \frac{\left\vert V_1 \right\vert}{\left\vert V_2 \right\vert}}</math>

For passive filters, <math>\left\vert V_2 \right\vert</math> will be smaller than <math>\left\vert V_1 \right\vert</math>. In this case, the insertion loss is positive and measures how much smaller the signal is after adding the filter.

==Link with scattering parameters==

In case the two measurement ports use the same reference impedance, the insertion loss (<math>IL</math>) is defined as:<ref>[[David M. Pozar|Pozar, David M.]]; ''Microwave Engineering, Third Edition''</ref><ref>Collin, Robert E.; ''Foundations For Microwave Engineering, Second Edition''</ref> 

:<math> IL = -20\log_{10}\left|S_{21}\right| \,\text{dB}</math>.

Here <math>S_{21}</math> is one of the [[Scattering parameters#Insertion loss|scattering parameters]]. Insertion loss is the extra loss produced by the introduction of the [[Device under test|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.

==See also==
* [[Mismatch loss]]
* [[Return loss]]

==References==
<references/>
*{{FS1037C}}

[[Category:Telecommunications engineering]]
[[Category:Engineering ratios]]