I think an excellent definition of the antenna and why it radiates is done
by John Kraus in his text, "Antennas" second edition. For radiation to
happen, there must be a discontinuity, or change of direction for the
antenna energy.
The half wave antenna can contain a cycle of high voltage at the end going
to minimum at the center, and then going back to a maximum at the other end.
The wave fits upon the half wave exactly. Of course, the current maxes out
at center of the half wave, and is minimal at the open circuit at each end.
There is the discontinuity. The half wave nicely facilitates the change of
direction (polarity).
Kraus helps the visualization of antenna action, by introducing the wave
upon the parallel feeder, then opening up the feeder end to form the
elements of the dipole.
This seems to help many students.
-K5KVH
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