Cecil Moore, W5DXP wrote:
"Years ago I experimented with two-element beams where both elements
were driven."

J.D. Kraus, inventor of the W8JK beam obviously did too. He found the
most gain he could get is the configuration of the W8JK. Some of his
results are summarized in Table 6-2 on page 192 of the 3rd edition of
"Antennas".Cecil has this book, I believe. Kraus reports the W8JK gain
as 6.1 dBi.

The W8JK has two dipoles spaced at 1/8 wavelength and fed 180-degrees
out of phase. Close coupling causes super gain but a very low drivepoint
resistance. Kraus calculates the drivepoint impedance as 9+j48 ohms on
page 186.

Best regards, Richard Harrison, KB5WZI