D37 — Closed-form impedance models from the papers

Decision

Closed-form models: Hammerstad & Jensen microstrip, Cohn/Wheeler stripline, Kirschning & Jansen coupled microstrip, Cohn coupled stripline, Ghione & Naldi GCPW; off-centre striplines by Wadell's image split; quasi-static, solder mask ignored; width/gap by integer-nm bisection

Alternatives

A 2-D field solver; KiCad's calculator code (GPL, and its coupled-stripline thin-gap branch drops √εr)

Reason

Same physics as KiCad's PCB calculator so users can cross-check; independent implementation from the papers; deterministic; agreement with KiCad 0–3 % and with exact conformal results to 1e-6 (doc 15 §14.5)