Figure 39. Solid pattern produced by horizontal half-wave
antenna located a half-wavelength above ground.
d. Vertical half-wave antenna.
Ground reflection also affects
vertical antennas.
See figures 40 and 41.
Notice that a vertical
antenna erected 1 quarter wave above ground has two lobes.
As the
height is increased, the number of lobes increases.
An antenna 1
wave length in height has 6 lobes.
e. It now can be seen that the ground reflection factor and the
antenna height play a major role in the radiation of radio energy.
In later sections we will see that we can select a particular antenna
height for a certain distance of transmission.
For example, for
short distances the antenna height should be less than a quarter
wave. For long distance communication, the antenna should be a half
wave or more in height. We can improve the ground reflection through
the use of a counterpoise or radial ground.
This increases the
conductivity of the earth and lessens the energy lost going into the
earth.
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