I understand that in Siberia that there is such an HF curtain array that has
26dbi gain.
I guess is operates 9 mhz ... 21 mhz bands, but information on former USSR
curtain array antennas in Siberia is quite limited as GOSTELCOM (the Russian
Telecom PTT) that runs these sites is mum on the technology.

All of these directional arrays are slewable, typically (- / +) 15 degrees,
giving a 30 deg coverage region.
VOA Delano is the nearest equivalent in the west, it is a HRS 12/6/1. TCI
sells the base antenna, but you will have to look in the data sheets area of
the website because the document is not mounted with the main HRS antennas.

A full blown HRS 12 / 6 / 1 goes for about 12,000,000 USD -- dammed cheap!

The most amazing thing is that there are MW transmission sites in Russia
with 26 dbi gain -- and designed for skywave reception.

PS: these sites can be used for other uses than SW broadcasting like SW
based RADAR, and Ionspheric research.

-- text --
With enough radiators arranged in the right order, 26 dbi gain is easily
obtained -- and the need for extremely high power transmitters is reduced.
Directional gain antenna systems make modern broadcasting possible...

-- reply to text --
26dBi is a LOT of gain- especially if you are talking about HF- as your
references are. Obviously, the array would have to be fixed as it would need
to be in excess of 9 wavelengths long if it were a Yagi (arguably the
highest gain array for its size).

At 7MHz this would be somewhere around 26 elements each in the neighborhood
of 66' and occupying a total length in excess of 1200'. Without going to my
texts, I would guess the 3dB BW of such an array to be in the 10 degree
region- not much coverage.

Dale W4OP