The Future of Balun & UNUN Modeling: A Peek into New Research
Every ham who has wound a 49:1 or 64:1 UNUN for an EFHW knows the story: stack ferrite cores, wind some turns, test, adjust, and measure. It works, but it’s trial and error. Wouldn’t it be great if we could simulate the whole thing with accuracy before ever winding a single turn?
A group of researchers — Viviana Giunzioni, Alberto Scazzola, Adrien Merlini, and Francesco Andriulli — have been working on just that kind of breakthrough. Their recent IEEE paper (behind the paywall, of course) isn’t about baluns directly, but about stabilizing the math behind low-frequency full-wave solvers. And that could eventually change how we design and understand ferrite cores, baluns, and UNUNs.
Why Simulation Struggles with Our Cores
HF cores and baluns operate in what mathematicians call the “low-frequency regime.” That doesn’t mean 3 MHz is low like audio — it means our cores and windings are electrically tiny compared to a wavelength. At those scales, the usual full-wave solvers (MoM, FEM, BEM) get unstable. They lose accuracy, especially with lossy materials like ferrite. That’s why most software falls back to quasi-static approximations that don’t capture the full picture.
What’s New Here
The Politecnico di Torino and IMT Atlantique team proposed a new way of handling these low-frequency problems. Instead of letting the math collapse, they reorganized the current components inside the solver so it stays stable across:
- the quasi-static zone (where displacement currents dominate),
- the eddy-current zone (where conductive losses rule), and
- the skin-effect zone (where current hugs the conductor surface).
In plain words: they’ve created a framework that lets you model a toroid, windings, and dielectric supports across the entire HF range without switching to a different solver or losing accuracy.
Imagine being able to run a solver that tells you not just the impedance transformation ratio of your 160 m EFHW UNUN, but also:
- how much core loss is happening at 1.8 MHz vs 7 MHz,
- how the winding capacitance shifts your resonance,
- where the hot-spots in the ferrite will be at 1 kW,
- and how common-mode impedance really distributes through the core stack.
But Let’s Be Clear
This is early academic work. Don’t expect HFSS or CST to suddenly give you “perfect EFHW balun models” in the next release. Right now, this stabilization lives in research code and journal articles. It will take time — perhaps years — before these methods trickle into the tools that hams and small RF shops can access.
The Long Game
For now, we still rely on measurements, equivalent circuits, and classic ferrite datasheets. But the fact that researchers are solving the low-frequency breakdown problem means that one day, we may not have to wind and burn test cores to see what works. Instead, we could prototype in software with confidence — just like RF engineers already do at VHF and above.
Mini-FAQ
- Is this usable for hams today? — No. It’s research-level math, not a practical design tool yet.
- Who’s behind the work? — A team led by Giunzioni, Scazzola, Merlini, and Andriulli (Politecnico di Torino & IMT Atlantique).
- What’s the potential? — Accurate, full-wave modeling of ferrite cores, windings, and baluns across the HF spectrum.
- When might we see it? — Likely years down the line, once commercial solvers adopt these techniques.
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