The 24th On-Wafer Users’ Forum, held during IMS-2026 and ARFTG-107 in Boston on June 11, 2026, brought together 48 participants from industry, metrology institutes, and academia. Chaired by Gia Ngoc Phung (PTB, Germany), the session centered on a question that matters whenever calibration accuracy is at stake: why can two valid implementations of multiline TRL (mTRL) give different answers, and what does that mean for on-wafer measurement confidence?

Three presentations approached that question from complementary angles.

Ziad Hatab (Keysight Technologies, USA) opened with “Rethinking the Math Behind Multiline TRL Calibration,” revisiting the mathematical formulation underlying mTRL and how it can be expressed and interpreted. James Skinner (NPL, UK) followed with “An Alternative Approach to Multiline TRL Calibrations,” presenting a different methodology aimed at improving the robustness and practical application of the technique under real measurement conditions. Shuhei Amakawa (Hiroshima University, Japan) closed with “Reappraisal of S-Parameter Basics in Light of 4-Port TRL De-embedding,” returning to fundamental S-parameter concepts and their implications for multiport de-embedding.

Taken together, the talks traced a single thread — from the mathematics of the calibration, through its implementation, to the interpretation of the de-embedded result.

The discussion that followed stayed close to measurement science. Several themes recurred: that mathematical equivalence between formulations does not guarantee numerical equivalence; that implementation details — line selection, probe contact, and measurement noise — interact with the calibration method itself; that the choice of de-embedding model shapes how the resulting S-parameters are interpreted; and that independent verification remains essential to validating calibration quality. None of these points is new on its own, but the session connected them in a way that made their interaction clear.

The strong participation throughout reflects continued community interest in the rigor and reproducibility of wafer-level calibration as on-wafer measurements push further into the mm-wave and sub-THz range.

We thank the speakers and all who joined the discussion. Looking ahead, the 25th On-Wafer Users’ Forum is in planning and will take place during EuMW-2026 week in London, UK, October 4–9, 2026. We look forward to seeing you there.

If you have an idea for an upcoming forum topic, or would like to share your own measurement experience, we encourage you to reach out to the ARFTG Users’ Forums Chair at [email protected].

Gia Ngoc Phung

ARFTG ExCom,
Users’ Forums Chair

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