I mean, it's nothing unusual, easily enough derived from principles; and, you mentioned EMC, but if you're kind of excluding EMC references, I dunno, EMC uses a lot of antennas, baluns and other cable-impedance-modifying and coupling structures so it's pretty much the go-to domain to find electromagnetic structures and tricks like this.
For example, a typical EMC cable clamp for measuring / injecting signals on cables/harnesses, uses a tall stack of ferrites, alongside a coupling strip that's grounded to plane at one end and couples to the cable at the other end. Thus giving isolation along the cable, coupling to a BNC... it's a clip-on bias tee, pretty nice eh?
And I say "easily enough", but those principles aren't exactly the most common information, you can pick it up from an undergrad curriculum I would say, but you're more likely to find it in explicit detail in grad level EE, and if you're not officially EE at all, it can take quite a lot of study and insight to develop these ideas, and many working in electronics never get there at all, it's just not in their wheelhouse (say, those working with audio, equipment repair, digital/embedded, etc.). It's fairly specialized knowledge, and so you have to search it out in particular, it won't come to you on its own, so to speak.
If you're confining yourself more to radio references, and ham stuff in particular, or online references even more narrowly, yeah there's a lot of junk information there unfortunately. There are a lot of RF and EMC engineers that are hams,
but there are few hams that are RF engineers. It works one way but not the other. So that selection slices the literature the wrong way and you...don't get very good results.
The tipoff is, such results -- postings, web pages, informal articles -- rarely cite anything; they should only be used as possibly correct information subject to further proof. When they do make citations, whatever of those references you can find in turn, check that they support the claims, that the claims are reasonable given what theory you know or are able to test, etc. You are searching for proof of correctness of the claims, and of the supporting material in turn, recursively, until you have reduced the problem all the way to well-proven claims and verifiable theory. Burdensome at first, but as you map out available knowledge, you can pin more things as proven, or in what ways they claim things correctly and what others they miss and haven't yet proven as such. This is the challenge of academic rigor, and the primary means of identifying, developing and curating well-proven science.
So, you see claims from, say, someone selling an antenna kit -- maybe they claim directionality/bandwidth/size beyond the theoretical (Chu–Harrington) limit, but if they provide no test results (feedline impedance or SWR or etc.; CM current; exact configuration/geometry tested; radiation pattern, at least along axes; calibration where possible; etc.), feel free to ignore their claims, doubt them fully, it's just a bunch of words it doesn't mean anything in relation to anything else until proven as such. And indeed, you will find claims of impossible performance, where the configuration is basically an unbalanced dipole let's say, but it's far wider bandwidth and higher gain than should be possible, and the only possible resolution to that is ground effect and feedline acting as antenna element, and perhaps nearby structures acting as reflectors if it was actually measured for radiation pattern. Or another common "trick", they're claiming SWR is antenna efficiency, or gain even, when this is only true when the antenna is lossless, and they might've simply cooked up a particularly shite configuration with a lot of equivalent resistance so the actual efficiency is awful but the bandwidth is wide and SWR is low. Again, verifiable claims, consistency, does it match theory, are the methods correct, etc. etc.
Regarding balun design specifically, you probably don't find many references discussing interwinding capacitance, but the problem can be decomposed into the N-turn impedance of a ferrite bead or other core, which you sometimes see plotted in datasheets, and yes the peak goes to higher Z at lower F as turns goes up as one would expect, and, you can test this independently by rescaling the problem say to magnet wire on a smaller core, it doesn't have to be coax -- and then substitute solid wire for coax and the outside fields / shield/CM impedance don't know the difference -- it
can't know that there's a wire inside the shield -- and that's your answer, that's the CM impedance across the balun from shield to shield, an impedance that isn't shared on the signal wire and therefore imbalances the result. And by scaling, I mean the frequency response is proportional to length scale, give or take material invariants (paramagnetic resonance perhaps, but most applications are well below that and ferrite just looks like a bulk lossy permeable material as we usually model it, plus minor wave effects due to core size and shape). So it's not a balun design problem, it's a transformer or inductor design problem, and you will likely find many more results in that more general direction, than for baluns alone.
Beyond that, you can do some hand-wavey thoughts about fields within and around the ferrites, because dielectric constant is fairly high so the tubular stack itself looks like a fat wire above a ground plane, and that impedance adds with the total bead impedance; fields and waves means wave mechanics and you could have cavity resonances or radiation or whatever depending on if the stack is in an open or closed configuration (open as shown, or closed in a box / surrounded with shield). Pretty soon, you'd want to measure or simulate these, but likely these are also to a degree of precision unnecessary (e.g. maybe if you were doing a VNA with a precision directional bridge, but for an antenna, who cares), and so we can truncate our efforts depending on accuracy required.
So, applying these principles, let's say, this:
http://on5au.be/content/a10/trans/41balun-2.pdfNo references (or maybe inlined, I just skimmed), but lots of measurements of basically what you're doing, different orientation (1:4 instead of 1:1+1), lower frequency (but why stop so short, first resonance might be 100s MHz) but we have every expectation it works to much much higher, and the measurements being very flat in the range tested certainly checks out with expectations.
Ooh, this is a good one:
https://www.nonstopsystems.com/radio/frank_radio_baluns.htmI wonder if this is kind of the holy grail that you've been looking for forever but just never found (probably because Google sucks these days); the references aren't necessarily high-tier journal results, but it looks like a reasonable selection of experimental data that can be checked in turn. (And local copies are provided for easy viewing!)
https://www.nonstopsystems.com/radio/pdf-ant/BALUNS2006-ang.pdfThis is one of the references, it seems familiar, I might've seen it a long time ago, but anyway -- showing off cores and some basic geometry, and more or less confirming the manufacturers' curves on these (at least of the EMI bead parts where impedance is most likely to be provided -- you'll have to look them up and confirm), and showing testing methods, and a range of typical applications. Good stuff.
...Maybe the formatting is a bit gaudy? I mean, it's no \$\LaTeX\$ article.
But what do you expect, it's PowerPoint, that's easily excused -- don't let superficial aspects like aesthetics get in the way of some good data. (Now, when it's poorly presented/arranged data, or misleadingly formatted, by all means critique; such aspects go a little deeper in meaning and impact!)
Tim
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