Antenna Modeling (NEC, EM Sim)

4nec2, MMANA-GAL, xnec2c, openEMS — design and simulate antennas before you cut wire.

Modeling an antenna in software before stringing wire saves you hours and prevents wasting expensive coax on a doomed design. The dominant engine is NEC-2 / NEC-4 (Numerical Electromagnetics Code), originally released in the 1980s and now wrapped by half a dozen GUIs. openEMS is the modern FDTD alternative for everything NEC can't do — micro-strip, complex 3D structures, dielectric materials. Cross-link with Spectrum & VNAs (NanoVNA / TinySA for measuring what you built), Circuit Simulation, PCB / EDA Suites (for PCB-trace antennas).

NEC-2 GUIs

★ 4nec2 (Arie Voors) — Windows; freeware (closed); the de-facto hobbyist NEC-2 GUI. Schematic editor, geometry visualizer, frequency sweep, SWR / impedance / pattern plots, optimizer. The default for HF / VHF / UHF wire and tubular antennas.
- https://www.qsl.net/4nec2/
★ MMANA-GAL (JE3HHT, BU2BW) — Windows; freeware; MININEC engine (NEC-2 cousin). Faster than 4nec2 for moderate-size models; preferred by some HF wire-antenna designers. Closed.
MMANA-GAL Pro — paid (~$20); commercial extension.
★ xnec2c — Linux / Mac; GPL FOSS; full NEC-2 engine + GTK GUI. The Linux open-source NEC-2 standard.
- https://www.5b4az.org/
NEC2C / NEC2++ — CLI NEC-2; FOSS; the engine many GUIs wrap.
NEC4WIN — Windows; closed; older.
CocoaNEC — macOS-native GUI; free.
EZNEC Pro — Roy Lewallen W7EL; Windows; was paid (~$100) until W7EL retired in 2022; now free (latest version released into the public). Superb classic NEC GUI. Closed.

Modern FDTD / FEM simulators

★ openEMS — Thorsten Liebig DG7XX; GPL FOSS; FDTD (Finite-Difference Time-Domain) electromagnetic simulator. Handles microstrip, PCB-trace antennas, complex 3D structures, dielectric substrates that NEC can't. Octave / Python interface; Paraview for 3D field visualization. Steeper learning curve than 4nec2 but enormously more capable for non-wire antennas.
- https://www.openems.de
Sonnet Lite — Windows; closed; freeware tier of commercial FEM tool; planar microstrip simulation.
Ansys HFSS / CST Studio Suite / FEKO — commercial; $5k–$50k+/year; lab / corporate territory; real EM-simulation industry standards.
Antenna Toolbox (MATLAB) — paid; ties into MATLAB licenses.
Empire XPCcel — commercial FDTD; less common.

Microwave / RF circuit simulators

★ Qucs-S / Qucsator — see Circuit Simulation; FOSS; useful for RF-network simulation (matching networks, filters, baluns). Limited compared to commercial.
AWR Microwave Office — commercial; the industry tool for matching-network design.
scikit-rf (Python) — see Spectrum & VNAs; Touchstone / S-parameter math; great companion to NanoVNA measurements.

Wire / structure design helpers

Wireframe / parametric modelers — most antenna designers sketch in 4nec2 directly; some use OpenSCAD / FreeCAD to build wire geometry parametrically and export .NEC decks.
Yagi designs from W6NL / DK7ZB / W8WWV — published optimized yagi designs; load straight into 4nec2.
SimSmith (AE6TY) — Windows; freeware; Smith-chart matching-network design; complementary to NEC.

Practical guidance

NEC-2 limits. NEC-2 assumes thin-wire models (segments much longer than wire diameter, segments shorter than λ/10). Doesn't model dielectric / metal sheets / magnetic loops well. For loops, traps, fat tubular elements, use NEC-4 or openEMS.
Segmentation matters. Too few segments and the model lies; too many and it's slow. Rule of thumb: 15–20 segments per λ, finer near feed-points and bends.
Ground model. "Free space" vs "real ground" gives wildly different results for HF antennas. NEC-2's "real ground" is a Sommerfeld approximation that's good for ~5° elevation and above; for very low-angle radiation use NEC-4.
Validate against measurement. Build the antenna, sweep with a NanoVNA, compare modeled vs. measured impedance. Discrepancies typically come from the feed-line common-mode current (add a choke balun) or ground proximity (raise it higher).
Optimize for SWR + gain + F/B. 4nec2's genetic-algorithm optimizer can spin up a 7-element Yagi spec in 20 minutes. Don't optimize blindly — always know what knobs the optimizer is turning.
PCB antennas need openEMS, not 4nec2. Inverted-F, meander, chip-antenna footprints — NEC will lie. openEMS or Sonnet Lite is the right tool. See PCB / EDA Suites.

License / pricing notes

4nec2 / MMANA-GAL / EZNEC Pro / CocoaNEC / Sonnet Lite — closed, free.
xnec2c / openEMS / NEC2C / Qucs-S / scikit-rf — FOSS (GPL).
MMANA-GAL Pro — paid (~$20).
HFSS / CST / FEKO / AWR Microwave Office — paid (commercial license).
EZNEC Pro went free in 2022 — the once-paid antenna modeler that many HF designs reference.

Pick this if…

Default 2026 hobbyist NEC GUI, Windows: 4nec2 (or EZNEC Pro now that it's free).
Default Linux NEC GUI: xnec2c.
HF wire antenna optimization: MMANA-GAL or 4nec2.
PCB / microstrip / 3D structure: openEMS.
Free planar microwave simulation: Sonnet Lite.
Validation after the fact: scikit-rf + a NanoVNA-H4 / LiteVNA-64.
Commercial / publishable EM simulation: HFSS, CST, or FEKO — your employer paid.