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...

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