engineering

Insertion loss

Insertion loss is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Insertion loss rather than just read about it. In short: In telecommunications, insertion loss is the loss of signal power resulting from the insertion of a device in a transmission line or optical fiber and is usually expressed in decibels (dB). If the power transmitted to the load before insertion is PT and the power received by the load after insertion is PR, then the insertion loss in decibels is given by, I L ( d B ) = 10 log 10 ⁡ P T P R {\displaystyle IL(\mathrm {d…

Key takeaways

Insertion loss belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Insertion loss to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Insertion loss from memory before moving on to harder problems.

Reference excerpt

In telecommunications, insertion loss is the loss of signal power resulting from the insertion of a device in a transmission line or optical fiber and is usually expressed in decibels (dB). If the power transmitted to the load before insertion is PT and the power received by the load after insertion is PR, then the insertion loss in decibels is given by,

I L ( d B ) = 10 log 10 ⁡ P T P R {\displaystyle IL(\mathrm {dB} )=10\log _{10}{P_{\mathrm {T} } \over P_{\mathrm {R} }}}

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 ( | V 1 | {\displaystyle \left\vert V_{1}\right\vert } ) to the signal level with the filter installed ( | V 2 | {\displaystyle \left\vert V_{2}\right\vert } ). This ratio is described in decibels by the following equation:

Insertion loss (dB) = 10 log 10 ⁡ | V 1 | 2 | V 2 | 2 = 20 log 10 ⁡ | V 1 | | V 2 | {\displaystyle {\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 }}}

For passive filters, | V 2 | {\displaystyle \left\vert V_{2}\right\vert } will be smaller than | V 1 | {\displaystyle \left\vert V_{1}\right\vert } . 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 ( I L {\displaystyle IL} ) is defined as:

I L = − 20 log 10 ⁡ | S 21 | dB {\displaystyle IL=-20\log _{10}\left|S_{21}\right|\,{\text{dB}}} . Here S 21 {\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.

Worked examples

Example 1 — a first encounter with Insertion loss

Start with the simplest possible case. Write down what Insertion loss claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Insertion loss before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Insertion loss ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Insertion loss

In research: Insertion loss appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Insertion loss in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Insertion loss is common in secondary-school and first-year university syllabi. It links to neighbouring topics Engineering ratios, Telecommunications engineering, so understanding it makes those chapters shorter.
In everyday life: Look for Insertion loss outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Insertion loss in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Insertion loss means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Insertion loss out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Insertion loss in simple terms?

Why does Insertion loss matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Insertion loss?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Insertion loss.