I have to disagree with your comments in Reply #5. You may not think, or may not have found there to be any legitimate differences between the various 'sizes' of antennas, but there are quite a few of us who have seen those so called 'magical' differences...
I'm always willing to be corrected with valid technical information - I'm mostly concerned with getting
the correct data presented to readers than I am to defending a particular position.
But if you look at the current distributions on the various antennas they are nearly identical. For
example, the difference between 1/2 wave and 5/8 wave radiators is a small amount of out-of-phase
current at the base of the 5/8 wave that actually reduces the effective radiation broadside to the
antenna. Similarly a ground plane with sloping radials turns itself into a half wave dipole as the radials
are sloped further downwards - there isn't any specific point where the performance suddenly shifts.
All of these are, in effect, half wave radiators, along with a J-pole (an end-fed half wave with a quarter
wave matching stub.) And, while you can make them worse than the theoretical half wave dipole due
to high losses, feedline currents, etc., you can't make them any better.
So electrically they really are basically the same antenna, with some minor differences in feed system
and construction. That's why I say that none of them can be significantly better than the rest.
However, they can be installed differently, and this is where the observed differences come into play.
If you put the feedpoint of your antenna at ground level and swap out 1/4, 1/2 and 5/8 wave radiators,
you likely WILL see a difference - that is because the point of maximum radiation is at a different
height above ground. This is why my statements were conditioned with the TOPS of the antennas
being at the same height. The point of maximum radiation is 1/4 wavelength down from the top,
and this cancels out the effect of the height above ground from the comparison.
This might seem like nitpicking, but it is actually important for understanding the differences
between two antenna options: without it, an antenna on top of a 10' mast would be different
than the same antenna on top of a 20' mast. By breaking the behavior into two pieces (the
antenna in free space, and the effects of the height above ground) we can make a much more
realistic assessment of what differences to expect between two antennas.
For example, I've seen claims such as, "I replaced my old dipole with the fancy XYZ antenna and
my signal improved by 20dB." If the XYZ antenna is equivalent to a dipole, I might still believe
this statement, but I'd attribute the improvement to something other than the difference in
the theoretical performance of the two antennas. (Mostly likely the coax was lossy or one
side of the old antenna was broken at the feedpoint.) Or "my new beam antenna is 20dB better
than my dipole" when the beam can't be expected to have more than 5 to 6dB gain. In that
case most of the difference may be due to the fact that the beam is mounted on a new tower
at 70', while the dipole was laying on the roof of the back porch.
So, yes, if you are comparing different antennas mounted on your porch rail, the 5/8 wave is
probably going to show an improvement over the 1/4 wave ground plane (especially if there isn't
enough ground clearance to slope the radials downwards.) But if the ground plane were put on
top of a mast so that the top was at the same height as the top of the 5/8 wave radiator, the
difference would be difficult for most hams (or CBers) to detect.
Is this a valid comparison? It depends on the construction. If I have a fixed mounting point it
might not be, but often I can construct a ground plane + short mast using the same materials
as a 5/8 wave or J-pole, and with the same overall height. If I am limited to the maximum
height I can go without needing guy wires, or am hoisting my antenna up using a rope tossed
over a tree branch, then any of them would work about as well.
This importance of understanding this is to see that, all other things being equal, I can choose the
one that is easiest to construct using the materials at hand without worrying that it might not be
as good as the others.
Again, I'm happy to be corrected if I've said something that is technically incorrect. But as far as
I know it is consistent with the current distributions on the antennas, and that is what determines
the radiation patterns.