Roy Lewallen wrote:
John Popelish wrote:


Picture a half wave disk of metal as the ground plane, producing the
inverted image of the vertical. . .


It appears that what I've been writing the past few days either isn't
being read or isn't being believed. Among it is an explanation of why a
"ground plane" doesn't produce an "image" of the vertical.

Since you appear to continue to believe this, please explain the
mechanism by which you think a half wave disk produces an "image" of the
vertical.

The disk forms an image by allowing the electric field lines to
terminate perpendicular to the "mirror" surface on exactly the same
lines as if they were heading toward a lower half of a dipole, while
the radial currents in the "mirror" allow the magnetic field lines to
encircle the monopole in the same pattern they would form if the
missing half of the dipole were in position.

This same pattern of electric and magnetic fields above the "mirror"
produces (half of the) photons that the full dipole would have
produced. A half wave diameter disk is about the minimum size
"mirror" that will keep the field patterns close enough to those of
the dipole to launch those photons. A larger disk would do better,
but not a lot better.