The viewer, cascade calculations and numerical limit checks can support commercial engineering work, but their results are only as meaningful as the underlying measurement, assumptions and reference planes.
The user is responsible for ensuring the VNA was calibrated appropriately and that the reported S-parameter reference planes correspond to the intended DUT boundaries. Fixtures, adapters, cables and de-embedding can materially change the result.
S-parameters are defined relative to reference impedances. RFellow displays the reference Z₀ parsed from supported Touchstone files and requires compatible Z₀ for the current cascade implementation. A different normalization can produce different S-parameter values.
Limit checking operates on the data available in the file. A sparse frequency sweep can miss a narrow resonance between samples. Cascade interpolation creates a common frequency grid but does not create new measured information.
A numerical PASS means all configured requirements were evaluated on the available sampled points and met their limits. Missing required S-parameters, uncovered sweep bands and unusable data produce INCOMPLETE rather than a verified PASS; a measured violation produces FAIL. Even PASS does not establish behavior between sample points or include calibration uncertainty, connector repeatability, environmental variation, production guard band, regulatory requirements or independent verification unless the user explicitly accounts for them.
A derived cascade models direct connection of the represented two-port reference planes in the chosen order. Any real cable, PCB trace, adapter, bias network or fixture between stages must be included as its own network if its effect matters.
RFellow is an independent engineering tool and is not a certification authority or an endorsement by Keysight, Rohde & Schwarz, IEEE, the IBIS Open Forum or any other referenced organization.
This preview text is product-design guidance, not a substitute for final legal review before a public commercial launch.