On Thursday, July 12, 2012 3:30:02 AM UTC-5, Rob wrote:
But in a dipole antenna, the currents in the two wires do flow in the
same direction. So a dipole radiates.

Sorry, there are two currents, forward and reflected, flowing in opposite directions on a standing wave antenna. A 1/2WL dipole is a standing wave antenna where the SWR at the ends is infinite and the SWR at the feedpoint is ~20:1. There is forward and reflected wave energy flow on each element of the dipole. At the ends of the 1/2WL dipole the forward and reflected currents are 180 degrees out of phase and equal in magnitude so they phasor add to zero, i.e. a standing wave current minimum (null). Since the forward and reflected current phasors rotate in opposite directions, they are in phase at the feedpoint and phasor add (constructively interfere) to a standing wave current maximum (loop) and most of the radiation is from the center of the antenna.

The feedpoint impedance of a dipole is Zfp = (Vfor+Vref)/(Ifor+Iref) phasor math.
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73, Cecil, w5dxp.com