learned, radio energy goes into the earth before it is reflected.
The conductivity of the earth will determine how deep the signal will
penetrate and how much of the signal is reflected.
Figure 37.
Reflection produced by ground plane.
3.
Ground-Affected Radiation Patterns.
a. Reflection factor. If we assigned the direct wave a value of
1 and the ground reflected wave a value of 1, then the maximum signal
we could have would be 2.
As we see from Figure 38, there are
varying vertical angles of maximum and minimum radiation lobes. The
number of lobes vary as the height of the antenna above ground is
increased.
b. Horizontal half-wave antenna.
Let's apply the reflection
factor to a horizontal antenna erected at distance above ground.
Notice figure 38. Patterns A, C, E, and G are the vertical radiation
patterns.
Patterns B, D, F, and H are the vertical radiation
patterns at right angles to the antenna.
Figure 39 shows a better
picture of the radiation produced.
Both figures 38 and 39 show a
half-wave antenna.
c. Notice that in figure 38, as the height is increased from a
quarter wave length above ground, the lobe divides into two lobes.
Notice also that the number of lobes equal the number of quarter
waves. At four quarter waves or one wave length above ground, there
are four lobes. Notice also that for odd quarter wave heights above
ground the major lobe is at 90 degrees.
57
Previous Page
