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Airlines are used in TRL calibrations, and in calibration verification.
First of all, do we call these "air lines" or do we call them "airlines"? Keysight uses "airline" so we will go with that. Sorry, Maury!
There are two types of airlines: beadless and beaded. Beaded is kind of cheating, but it is way easier to use: just a tiny amount of dielectric is used to support the center conductor. Beadless airlines literally fall apart if they are not connected between adjacent connectors. If you want NIST quality calibrations, you must go beadless.
TRL (and LRL) calibration using airlines
In the video below, you will see someone perform a 1.85mm male-to-female (insertable) calibration using airlines that work to 67 GHz. It is a tedious process, and if you are not careful you will trash a $10,000 calibration kit before you eat your first donut of the day. Don't even think about having coffee before performing this procedure...
This video is part of Maury's Youtube channel, see more content here.
We say "kudos" to the operator who moves her hands slowly and deliberately. Nice use of a foam "jack stand" to help reduce the stress on the parts as they are assembled. In micro-electronics you don't want someone man-handling (are we still allowed to say that?) the equipment. One small point worth raising is that tapping the pieces to a "ground" to discharge ESD is not a great practice. The person doing the calibration in the video appears to wear a static strap on her left wrist, so this should not be necessary.
After watching this video, you might want to consider all of the other choices for calibrations, such as SOLT and ECAL, that do not use airlines. You might lose a small amount of accuracy, but your company will appreciate that the calibration kit will last for years with moderate use. The most accurate calibrations should be reserved for critical device characterizations such as load-pull. Which is what Maury is known for!
Airline calibration performed by Maury
The Maury TRL cal kit is described here. Maury provides a table of how the airline standards are applied across frequency:
DC — 0.8 GHz: TRM fixed termination (accuracy of TRM is acceptable, considering that an airline long enough to reach down to 10 or even 100 MHz would be impractical!)
0.8 — 4 GHz: use TRL 3 cm airline
4.0 GHz — 13.0 GHz: use TRL 0.96 cm airline
13.0 GHz — 67.0 GHz: use LRL (line/reflect/line) 0.96 cm and 1.15 cm airlines (here, the difference between the lengths is critical: 0.19 cm.)
For yucks, we applied our TRL calibration spreadsheet to these frequency bands, and came up with 3.13 instead of 3 cm, 0.88 instead of 0.96 cm and 0.19 cm (in full agreement), which overall are very close to what Maury used. However, we did not try to enforce that the difference between two of the standards needs to be 0.19cm, so that affected Maury's overall choice of cal standard lengths. You can grab your own copy of our TRL spreadsheet on our download page.
Airlines used in calibration verification
Airlines are used in calibration verification. Usually this includes a 50 ohm airline as well as a 25 ohm airline. This type of verification is also traceable to NIST standards.
http://literature.cdn.keysight.com/litweb/pdf/85051-90031.pdf