Cecil, W6DXP wrote:
"Bottom line: The currents flowing in a folded dipole are common-mode
currents which radiate, not transmission line currents which do not
radiate (much), and that`s a very good thing for an antenna."

Nicely said! Agreed that it is the common-mode currents which radiate,
but differential-mode currents exist too. At the tips of the folded
dipole, some current turns the corner and flows in the opposite
direction after its U-turn. This creates a situation much like the
reflection from the open circuit ends of the common dipole. At the
center of the continuous wire which ties the tips of the driven side of
the folded dipole together, the colliding currents have traveled the
same distance at the same velocity so they are still 180-degrees
out-of-phase. This amounts to a short-circuit, and in fact this amounts
to a zero voltage point which may be grounded without consequences in
most cases.

In the folded monopole (unipole), the currents into the input terminals
flow nearly as they would flow into any 1/4-wave short-circuit stub.
The difference seems to be that the grounded side of the transmission
line feeds both its side of the folded unipole and the ground plane,
creating an opportunity for imbalance and radiation. And, radiate it
does with very nearly the same characteristics as an open-circuit ground
plane antenna.

Best regards, Richard Harrison, KB5WZI