Support Boundaries

This page says what rfx supports today, feature by feature and port family by port family, and which combinations are refused. The maintained contracts, with their full evidence, are the support matrix and the S-parameter support matrix on GitHub. Defects you can hit inside these limits are listed in known limitations.

Status	Meaning
supported	Documented for routine use within the stated limits.
limited	Documented only for the geometry, mode, mesh or observable stated. Outside that, you have to validate it yourself.
experimental	Runs and has regression tests, but there is not enough RF evidence to rely on the numbers.
not documented	Code exists, but there is no public workflow.
unsupported	Refused with an error.

A clean preflight or a completed run does not move a feature up this scale.

Feature	Status	Limit
Uniform Cartesian Yee grid	supported	The baseline. Each source and observable still has its own limits.
boundary="cpml" / "pec"	supported
boundary="upml"	supported	Reflects about 25 dB more than CPML at the same layer count. Prefer CPML where the reflection floor matters.
precision="float32"	supported	The default.
precision="float64" / "mixed"	limited	Uniform single-device solver only. "mixed" raises the CPML reflection floor; not for S-parameters.
Isotropic, conductive and Debye/Lorentz materials	supported	Dispersive models within the validated subsets. sigma >= 1e6 S/m is lossless PEC.
Metal sheets, add_thin_conductor	supported	Lossless PEC sheet on one grid plane.
Lossy sheets, surface_impedance_f0=	limited	Band-centre surface resistance on its documented uniform and graded lanes. Not a general dispersive conductor model.
Probes and flux monitors	supported	On a uniform grid. See the graded-mesh table below.
Harminv resonances (find_resonances)	supported	Needs a rung-down record and some loss.
Far field / RCS (NTFF)	limited	Benchmarked cases in Far-Field and RCS.
Plane wave (add_tfsf_source)	limited	x-directed, 3-D or 2-D (TMz/TEz), CPML.
Graded meshes (dx/dy/dz_profile)	limited by feature	See Graded meshes.
ADI solver (solver="adi")	experimental	3-D PEC-cavity frequency within 2 % at adi_cfl_factor=2. Use Yee for results you report.
Subgridding (add_refinement)	not documented	run() on a uniform mesh only.
Multi-device runs (devices=)	not documented	Speed, not a separate accuracy claim.
Floquet / Bloch ports	experimental	No high-level S-parameter API.

Port	Calculator	Status	Limit
lumped add_port(...)	run(compute_s_params=True)	limited	One-cell feed model. About 60 cells per wavelength for one-port S11.
wire add_port(..., extent=...)	run(compute_s_params=True)	limited	Magnitude evidence is stronger than absolute calibration. Graded-mesh use is experimental.
lumped / wire	forward(port_s11_freqs=...)	limited	S11 vectors on the uniform single-device path.
add_msl_port(...)	compute_msl_s_matrix()	limited	Quasi-TEM (mode="laplace"), directions ±x and ±y. At least 4 cells through the substrate (preflight warns below that). Graded mesh experimental; mode="eigenmode" outside scope.
add_waveguide_port(...)	compute_waveguide_s_matrix()	limited	Uniform single-mode magnitude has broad evidence; phase, junctions and multimode less. S is a power-wave S only when all ports share one cross-section. Gradients on normalize=False and "flux". Graded mesh experimental.
add_waveguide_port(...)	run(...) → waveguide_sparams	limited	Per-port diagnostic, not the full matrix.
add_coaxial_port(...)	compute_coaxial_line_reflection(...)	limited	One face="top" port, self-contained line, float32 uniform grid. At least 4 cells across the annulus. The line absorbs on all three axes.
add_coaxial_port(...)	compute_coaxial_two_port(...)	limited	One SMA-class through-line family, symmetric discontinuities only.
lumped/wire + microstrip	compute_mixed_s_matrix()	experimental	Magnitude not validated; the default passivity projection alters the diagonal.
coax + microstrip	compute_coax_msl_transition()	experimental	Diagnostic only; the matrix is not passive and is refused by default.
add_floquet_port(...)	none	experimental	Diagnostic helpers only.
sources, TFSF, probes, DFT planes, flux monitors	none	not a port	No reference impedance, so no S-parameters.

Each family has one calculator. run(compute_s_params=True) handles lumped and wire ports only. sim.compute_s_matrix() picks the right calculator for you, except for a lumped/wire-only model, which it refuses (call run(compute_s_params=True)); see Sources & Ports.

Support on a graded mesh is decided per combination. A graded run completing says nothing about whether its S-parameters, flux or far field are accurate.

Combination	Status	Limit
Multi-band graded profile, ratio ≤ 1.4 on z (1.3 in-plane)	limited	Solver-level evidence (energy, transition reflection, order, gradients). Keep grading out of the absorber.
NTFF + graded z	limited	Short-dipole directivity within about 0.05 dB of theory; other cases need their own validation.
Lumped R/L/C + graded mesh	limited	Elements take part in the update; S-parameters and component-value gradients not documented.
DFT plane or flux monitor + graded z	experimental	Runs; no general accuracy statement.
Plane wave + graded mesh	experimental	Normal incidence along ±x only, with x uniform. Preflight warns when the propagation axis is graded.
Waveguide S-matrix + graded mesh	experimental	Single mode, normalize=True or "flux". One passed magnitude comparison (graded y, WR-90). No dz-graded accuracy evidence.
Microstrip S-matrix + graded mesh	experimental	mode="laplace"/"uniform"; internal checks only.
Wire-port S-parameters + graded mesh	experimental
Lumped-port (one-cell) S-parameters + graded mesh	unsupported
Coaxial port + graded mesh	unsupported
UPML + graded mesh	unsupported
Periodic / Floquet port + graded mesh	unsupported

rfx refuses these before the first time step instead of returning a number:

• one-cell lumped-port S-parameters, coaxial ports, boundary="upml", or a Floquet port on a graded mesh;
• mode="eigenmode" microstrip ports on a graded mesh;
• a plane wave on a graded mesh at oblique incidence or along ±z;
• a calculator called with the wrong port family, for example compute_msl_s_matrix() without microstrip ports; run(compute_s_params=True) computes lumped and wire ports only, and a coaxial port is not handled by run() at all;
• compute_coaxial_line_reflection(...) with anything else registered, a graded mesh, non-float32 precision, or a boundary other than CPML on all six faces;
• compute_coax_msl_transition() with a non-passive result, unless you pass strict_passivity=False;
• compute_waveguide_s_matrix(normalize=True) with a traced eps_override/sigma_override;
• a waveguide reference-plane shift that crosses cells of more than one size on a graded mesh;
• precision="float64" or "mixed" on a graded mesh, with devices=, or with subgridding;
• stencil_order=4 with CPML/UPML, a graded mesh, ADI, dispersion or the other features it does not support;
• the ADI solver with interior metal (sheets, wires or volumes);
• any run() argument the selected solver path does not implement, for example snapshots on a graded mesh or until_decay with ADI;
• add_refinement combined with forward(), optimize() or topology_optimize();
• devices= with exchange_interval other than 1;
• run(ringdown=...) with anything but wire ports, or with until_decay or devices=.

Some combinations off the main path still ignore a setting without raising, for example a Kerr material on a non-uniform run(), or mu_r and Kerr on the ADI solver. These are tracked as open issues on GitHub. If you need a feature on a path other than the uniform Yee solver, check there first.

Using a probe, DFT plane or flux monitor as if it were an impedance-defined port is unsupported for the same reason: it has no reference impedance or reference plane.

Exported files (Touchstone, HDF5, CSV, JSON, plots) record what a run produced. They do not change its status. When you report a number, state the API and port family, the mesh (uniform or graded, cell size), the frequency range, the normalization, the rfx version and the comparison you made. Outside a listed range, run a convergence study and compare against an analytic or independent reference first.