Roy Lewallen wrote in
:

....
A properly designed transformer has ...

I think the most common 4:1 balun in use is the Rutroff 4:1`balun.

If it is constructed as a bifilar winding on a ferrite core, and the
distance between wires is much less than the distance between turns
(which is commonly the case), it can be though of as a transmission line
wound on a core.

Rutroff suggested the transmission line equivalent in his original
article.

I have developed a transmission line model and solution in the draft
article at http://www.vk1od.net/balun/Ruthroff/RU1-4.htm . It predicts
both low frequency and high frequency departure from ideal
characteristics, and predicts core loss with different loads. The model
suggests that balun efficiency can easily be below 50% on extreme loads
using some typical commercial constructions. The model results have been
validated on a small number of prototype baluns.

Owen