Jeff Liebermann wrote:
"In my never humble opinion, there`s no way to provide any form of
diversity reception improvement with a single antenna, unless one also
uses two feeds, going to different receivers, and ending in either a
decision awitch or an intelligent combiner."

That is my experience too. Space diversity requires 2 or more antennas
and receivers. One antenna can serve separate receivers which are
connected to cross-polarized feeds using a single reflector for
polarization diversity.
Or, multiple receivers can be used on a single receiving antenna, but
transmission of more than one copy of the desired signal is required,
This is how frequency diversity is usually achieved. Two copies of the
same program may be modulated on the same carrier if it is shown that
the medium treats the sidebands differently so that when one is treated
badly the other may be solid. I`ve seen this done with selection of
upper or lower sideband from a double sideband transmission.

Best regards, Richard harrison, KB5WZI