ENGINEERING ANSWER
Total insertion loss includes conductor and dielectric attenuation, mismatch, launches, vias and components. It should be budgeted for a complete signal path at specified frequencies, temperatures and reference planes.
What to decide before release
Separate distributed line loss from discontinuities. Use multiple line lengths to help distinguish fixture loss from propagation loss. Review return loss alongside insertion loss so a mismatch is not mistaken for material attenuation.
Checks to put in your design brief
- List every path element
- State the measurement reference planes
- Keep margin for process variation
Important distinction
Do not promise a loss figure from the laminate data sheet without a defined circuit and test method.
Sources & basis
Material facts follow the cited source. Design checks are preliminary guidance, not supplier process instructions.