By Michelle Thompson, W5NYV
There is a title of software that almost every antenna modeler has heard of. NEC-2, the Numerical Electromagnetics Code, was released into the public domain by Lawrence Livermore National Laboratory in 1981. For decades it has been the engine underneath tools like EZNEC, 4NEC2, and xnec2c. It is the mathematical baseline against which antenna designs are validated. NEC-2 is the common language of the modeling community.
NEC-2 is a remarkable piece of work. However, curved antennas (helices, loops, spirals) are poorly modeled by its straight-segment approximation. Closely spaced wires behave badly. Thick conductors don’t act quite right. These are not implementation bugs. They are fundamental properties of the mathematical approach NEC-2 uses.
The solution to these limitations exists. It is called the Conformal Method of Moments with Exact Kernel (CMoM). This approach replaces NEC-2’s straight-segment approximations with curved segments. The NEC-2 kernel is replaced with the full cylindrical surface integral. This means that we get more accurate modeling for exactly the antenna types that matter most to ORI’s work, such as ground station helices, compact loaded dipoles, loops, and arrays.
There is exactly one production software implementation of CMoM with exact kernel in the world. It is proprietary and the current price is $1599 USD per year for the license.
Until now, that has been the end of the story for anyone who needed high-fidelity curved-wire antenna modeling without a commercial license. We decided to do something about that. Arcanum changes things.
What Arcanum Is
Arcanum is ORI’s new open source CMoM antenna simulation engine. It is, to the best of our knowledge, the first open source implementation of the Conformal Method of Moments with Exact Kernel.
The name is intentional. An arcanum is hidden or secret knowledge. The mathematical techniques underlying CMoM have been in the academic literature for decades. Champagne, Williams, and Wilton described the curved-segment approach in 1992. This reference is listed in the Arcanum bibliography. We assemble these approaches into an accessible, open, community-owned tool. That is what we are building.
Arcanum is written in Rust with Python bindings, which means it runs fast where it needs to (the numerical core) and it stays accessible where it counts (notebooks, scripts, integration with existing ORI tooling). It reads standard NEC file format, so every antenna model that has been ever built in EZNEC or 4NEC2 works immediately.
Where We Are Right Now
We have completed the design and documentation phase. Sixteen design documents covering every aspect of the engine, from geometry parsing, matrix fill, linear system solve, to post-processing, are written, reviewed, and committed to the repository. Every mathematical derivation is documented. Every test case is specified with expected numerical values before a single line of production code is written.
This is intentional. We are following a design-first process that many of us at ORI learned in industry: design, document, code, test. The heavy intellectual work, figuring out what to build and why, is done. This brings us to implementation, which is where our community comes in.
The repository includes reference antenna decks for immediate use. There is a classic half-wave dipole, a 3-element Yagi-Uda, an axial-mode helix over ground, and ORI’s own Dumbbell compact HF antenna. https://github.com/OpenResearchInstitute/dumbbell
The Dumbbell deck in particular reflects real ORI work. It was designed, built, and field-tested by the Washington DC team and then the San Diego team, and its measured SWR data over multiple builds gives us real-world validation ground truth.
Why This Matters for ORI
Arcanum is a contribution to the broader RF engineering community. Amateur radio operators, academics, and engineers who have been working around NEC-2’s limitations for decades will have a free, open, better alternative. Given how much of ORI’s own work builds on the tools and knowledge the amateur radio community has developed over generations, giving something substantial back is the right thing to do.
Get Involved
The Arcanum repository is live at ORI’s GitHub. GitHub Discussions and Issues are open. Questions about the design documents, proposed changes, and implementation planning are welcome. The #antenna-design channel on ORI Slack is active.
If you model antennas, write Rust, work in Python numerical computing, or just want to understand how antenna simulation actually works from the mathematics up, there is a place for you in this project.
Arcanum repository: https://github.com/openresearchinstitute/arcanum
ORI getting started: https://openresearch.institute/getting-started
#antenna-design on ORI Slack