"A uniform current flowing along the length of the (1/4٨)
whip is an idealized situation, however, since the current
is greatest at the base of the antenna and goes to a minimum
at the top. In practice, the field strength will be less
than that given by the above equation, because it is a function
of the current distribution on the whip. . .
the current is not uniform on a whip
antenna . . . The net result
is that most of the antenna current returns to ground near
the base of the antenna, and very little near the top.
Two things can be done to improve this distribution
and make the current more uniform. One would be to
increase the capacitance of the top of the antenna to
ground through the use of top loading or a capacitance
hat, . . . The other method is to place the loading coil
farther up the whip, as shown in Fig 7, rather than at the
base. If the coil is resonant (or nearly so) with the
capacitance to ground of the section above the coil, the
current distribution is improved as also shown in Fig 7.
The result with both top loading and center loading is
that the radiation resistance is increased, offsetting the
effect of losses and making matching easier."
ARRL Antenna Handbook ch.16
