Taking one's cue from the Alford Slot Antenna, let us propose the use of the
fields in
the air gap of a parallel plate capacitor as the source of RF radiation.

To do this, we will terminate our 50 ohm coax with a series LC circuit of 50
ohm
resistive impedances (so one will be 25+jX and the other 25-jX) at the
operating
frequency.

Very little of the energy supplied to our antenna will be radiated, and most
will be stored
as energy in the resonant LC circuit, until such time as the stored energy
outdoes the incoming energy,and
the LC circuit will now act as an energy source, sending it back down the
coax.

So, we'll have a short antenna, matched to its feeder, that is not radiating
all the power fed to it, and
is returning some of that power back down the coax.

(An even simpler case, although it would give a reactiv match, would be the
capacitor alone, but think
for one minute, why do you get the 90 degrees phase relationship between the
volts and current
in a capacitor? Because it acts like an energy source in its own right!