I do not think this has a biconical. The big triangular element is a reflector to improve the pattern at the lowest frequency. The elements are all fed by a wire transmission line along the axis, from the thin end, so that the signal radiates from the first half-wave wide part it finds, in a similar way that it would from a three element Yagi-Uda array. The big triangular element may not be fed. Most antenna engineering books will describe how these work and their construction, such as the antenna engineering handbook.

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Dear Malcolm, thank you for your answer, but it seems to me that triangular part looks like to be radiator as well. If you can zoom at the photo https://www.saelig.com/product/hyperlog-20600.htm you will see that they are not symetrical in both sides (one looks like a bit higher than another side) that might be fixing on the different phase beam. Some has biconical elements https://electro-metrics.com/product/antenna-biconical-em-6917b-2-26-mhz-to-3-ghz/

I would like to get any patent or structure, but looks like there are nothing in the books that I found regarding those hybrid antennas.

You may be right!

Those parts may be antennas. Some may be reflectors, though.

The triangular part and the biconical operate at slightly longer wavelengths than twice their length, but are probably not directional, but I'm not sure. There may be a diplexer in there, or these elements may just be fed by the end of the line feeding the log elements. I think the last of those is more likely and may give a better transition between the two. Putting the different element there gets extra bandwidth at the bottom where it is expensive in terms of size for a log-periodic, without the size that would be needed by continuing the log-periodic. There is probably a compromise in terms of polar diagram.

Thank you Malcolm

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