ENGINEERING ANSWER
A test fixture should introduce known, repeatable behavior so the device can be characterized. Fixture launches, line standards and reference-plane definitions are part of the measurement system.
What to decide before release
Design through, reflect or line structures according to the chosen calibration/de-embedding method. Keep materials and processing consistent with the device fixture and document line lengths carefully. Retain measured standards and construction records.
Checks to put in your design brief
- Choose calibration methodology first
- Control connector assembly
- Record reference planes and line lengths
Important distinction
A convenient test coupon is not automatically a valid calibration standard.
Sources & basis
Material facts follow the cited source. Design checks are preliminary guidance, not supplier process instructions.