The electrical length of a monopole is longer than its physical
length, because the velocity of propagation along the monopole is
slower than in free space.

Here are some parameters for two cases of base-fed, self-resonant, 1
MHz monopoles, with two ohms in the r-f ground connection, over a
perfect ground plane:

1/4-WAVE

Height = 70 meters
Width = 1.5 meters (solid cylinder)
Input Z = 38 + j0 ohms
Peak Gain = 4.9 dBi at zero degrees elevation
Number of Lobes in Elevation Pattern = 1

5/4-WAVE

Height = 368 meters
Width = 3 meters (solid cylinder)
Input Z = 63.5 + j0 ohms
Peak Gain = 7.57 dBi at 57 degrees elevation
Number of Lobes in Elevation Pattern = 3

Antenna current always is very nearly zero at the top of a monopole of
every height, and distributes itself below the top of the monopole
approximately in the form of a sine wave.

Monopoles of every height need a very low-loss return path for the
displacement currents they generate in the nearby earth, extending out
to about 1/2-wavelength. Current densities in the earth vary within
that distance for monopoles of different heights, and are
proportionally less very near a 1/2-wave monopole than very near a 1/4-
wave monopole. But for best system efficiency a 1/2-wave monopole
still needs a low-loss ground plane to work against.

An example of a low-loss r-f ground connection is 120 buried radial
wires extending about one-half of a free-space wavelength in three-
degree steps around the base of the monopole, and bonded together at
the base. Such a radial system has an r-f loss of 2 ohms or less.

RF