Ian, GM3SEK commented thoughtfully on many points regarding the rhombic.

It is an excellent antenna for fixed point communications.
Unfortunately, the earth and moon are not stationary with respect to
each other. The rhombic may not be so re-directable as antennas like the
Yagi or corner reflector.

For transmitting, the rhombic has a lower maximum voltage than a
resonant standing-wave antenna. For high power, it`s a consideration.

The power remaining at the far end of the rhombic has been recycled by
some to eliminaate waste.

Cecil does an excellent job of explaining where the power in a
transmission line goes. Unfortunately, re-entrant rhombics tend to lose
some of their advantages of simplicity and bandwidth in the elaboration
process.

On the subject of diversity, it works by switching to a better receiving
system. Without switching, spaced antennas only provide a phased array
in which destructive interference happens during some signal conditions.

Where I worked, we used triple diversity receivers with 3 rhombic
antennas spaced about 10 wavelengths apart at the low frequency end of
the spectrum. A Crosby or Pioneer combiner selected the best of the 3
receiver outputs to feed a program line. Several receiving systems
shared the same 3 rhombics for simultaneous program relay.

Sidelobes are only a small problem when using triple diversity and
selectable sideband in reception.

Best regards, Richard Harrison, KB5WZI