rfx

rfx is a 3-D finite-difference time-domain (FDTD) electromagnetic simulator built in JAX. These docs focus on maintained user workflows with explicit support boundaries.

Supported workflows

Start with the uniform Cartesian Yee FDTD solver. The table summarizes the documented workflows and their limits:

Configuration	Documented use
Uniform Yee RF workflows	recommended default for tutorials, examples, probes, Harminv, selected S-parameter calculations, and far-field calculations
Rectangular waveguide S-matrices	validated within the documented rectangular-guide geometry, mesh, and frequency limits
Lumped, wire, and microstrip-line port workflows	available through their matching calculators; validation scope follows the support matrix
Coaxial line reflection	float32 precision, nonperiodic 3D second-order uniform Yee grid, CPML on all six boundary faces with positive thickness on both z faces, cpml_axes="z", and exactly one face="top" coaxial port; see Sources and Ports for the self-contained calculator limits
Differentiable design loops	use proxy objectives, gradient checks, and documented validation before treating a design result as evidence
Studio, CLI, and MCP experiments	versioned local CPU runs, append-only revisions, replay bundles, and server-approved MCP actions; see the guide for the current UI scope

If a capability is not listed here or on the Support Boundaries page, treat it as outside the documented public support scope until that page lists it.

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Why rfx

Feature	Detail
GPU acceleration	JAX/JIT execution for large 3-D grids
Differentiable workflows	jax.grad through selected JAX-traced objectives; validate the final RF observable within its documented limits
RF workflow tools	materials, sources, probes, ports, S-parameter helpers, Harminv, far-field utilities
Recommended examples	the ordered tutorials under examples/tutorials/ (start at examples/README.md), plus the inverse-design examples
Documented limits	support follows the stated geometry, mesh, frequency, and calculator constraints, not every importable symbol

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Quick install

pip install rfx-fdtd

GPU support depends on your JAX/CUDA environment:

pip install "jax[cuda12]" rfx-fdtd

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Minimal example

from rfx import Box, GaussianPulse, Simulation

sim = Simulation(
    freq_max=5e9,
    domain=(0.14, 0.06, 0.05),
    dx=2e-3,
    boundary="cpml",
    cpml_layers=8,
)
sim.add_material("slab", eps_r=2.2, sigma=0.01)
sim.add(Box((0.07, 0.018, 0.018), (0.09, 0.042, 0.032)), material="slab")
sim.add_source(
    (0.03, 0.03, 0.025),
    "ez",
    waveform=GaussianPulse(f0=3e9, bandwidth=0.8),
)
sim.add_probe((0.11, 0.03, 0.025), "ez")

preflight = sim.preflight()
print(preflight.format())
preflight.raise_for_failure()

result = sim.run(n_steps=1200)
print(result.time_series.shape)

This records a dielectric pulse response without making a resonance or Q claim. Resolve any preflight warning introduced by model changes. Use the First Patch tutorial for a patch model that passes preflight and the checks required before reporting resonance or Q.

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Documentation by topic

Getting Started

• Installation — Python/JAX install, GPU notes, dev setup
• Quick Start — first simulation with the current high-level API
• Your First Patch Antenna — build a model, run a short check, and learn what is required before reporting RF results
• Studio, CLI, and MCP Experiments — local UI, versioned CPU runs, replay, and MCP approvals

Modeling & Setup

• Simulation API — Simulation, Result, auto_configure, ports, NTFF, and design helpers
• Materials & Geometry — library materials, Debye/Lorentz, CSG shapes, PCB stackup
• Sources & Ports — point sources, lumped/wire ports, microstrip-line ports, waveguide ports, and coaxial-line reflection for exactly one face="top" port within its stated limits
• Probes & S-Parameters — DFT probes, S-matrix helpers, Harminv, de-embedding, exports
• Memory Reduction — reduce FDTD/AD memory while preserving validation boundaries
• ADI Solver (experimental) — unconditionally stable ADI-FDTD for stiff meshes, its timestep-vs-accuracy trade, and what is validated
• Waveguide Ports — rectangular waveguide modal workflows

Analysis & Validation

• Cross-Validation & Accuracy — short public validation overview
• Benchmarks — quantitative benchmark summary
• Convergence Study — mesh refinement workflow
• Far-Field & RCS — NTFF radiation patterns and scattering workflows
• Visualization & Analysis — plotting, exports, post-processing

Design & Optimization

• Autodiff and Adjoint Background — Meep-informed gradient concepts for microwave engineers
• Inverse Design — autodiff-driven optimization with documented proxy objectives
• Gradient Behavior — where gradients are usually well behaved vs noisy
• Parametric Sweeps — sequential sweep and jax.vmap design-space exploration
• Patch Antenna Design — rectangular patch workflow

Secondary hubs

• Examples — recommended public runnable paths
• Validation — public support and validation overview
• Gallery — examples with their RF evidence and limits stated on each page
• API — curated public API contract