# The forward model, next to openEMS

Channel: development; package: 2.0.0rc1; source: 2c32b7cf79b796fae825bfa08fc73d9914e61723

Page: https://remilab.ai/rfx/showcase/forward-checks/
Source: https://github.com/bk-squared/rfx/blob/2c32b7cf79b796fae825bfa08fc73d9914e61723/docs/public/showcase/forward-checks.mdx

A gradient is only as useful as the simulation it differentiates. These two
boards are solved by rfx and by openEMS, and each comparison is a test in the
repository (`tests/crossval/rt5880_patch/` and `tests/crossval/msl_notch_filter/`).

Pending for 2.0 (tracker 1471). The curves on this page were computed with rfx 1.8.0 (commit
b46a8220), before the settling check judged each frequency bin a result reads. Both cases are
being re-measured under the current check, so this page quotes no agreement figure until that run is in
the repository. The notch filter's uniform-mesh ladder is not yet shown to converge on the drawn
600 µm line.

## Probe-fed patch on RT/Duroid 5880

  [Real and imaginary parts of the input impedance of the RT/Duroid 5880 probe-fed patch from rfx and from openEMS on its finest mesh, 2.0 to 2.9 GHz](https://remilab.cnu.ac.kr/share/7c02ad43c580/forward-patch/forward_curves_rt5880_patch_site.png)

The figure shows the real and imaginary parts of the input impedance from both
solvers. Neither model declares a probe radius, so each feed cell sets the
probe's series reactance; the two solvers' reactance curves differ for that
reason, and the case judges the resonance and the input resistance, not the
`|S11|` dip.

  [rfx_curves.npz](https://remilab.cnu.ac.kr/share/7c02ad43c580/forward-patch/rfx_curves.npz)
  [reference_curves.npz](https://remilab.cnu.ac.kr/share/7c02ad43c580/forward-patch/reference_curves.npz)
  [result.json](https://remilab.cnu.ac.kr/share/7c02ad43c580/forward-patch/result.json)

## Microstrip open-stub notch filter

  [|S21| and |S11| of the microstrip open-stub notch filter from rfx and from openEMS on its finest mesh, 2 to 7 GHz](https://remilab.cnu.ac.kr/share/7c02ad43c580/forward-notch/forward_curves_msl_notch_filter_site.png)

A 12 mm open stub on a 50 Ω microstrip line (254 µm, εr 3.66) is a quarter wave
near 3.7 GHz, where it shorts the line. The figure shows |S21| and |S11| from
both solvers.

  [rfx_curves.npz](https://remilab.cnu.ac.kr/share/7c02ad43c580/forward-notch/rfx_curves.npz)
  [reference_curves.npz](https://remilab.cnu.ac.kr/share/7c02ad43c580/forward-notch/reference_curves.npz)
  [result.json](https://remilab.cnu.ac.kr/share/7c02ad43c580/forward-notch/result.json)

Each comparison holds for its board, mesh, band and observable.