TC 9-64 _________________________________________________________________________
while others may be parallel. Such an arrangement is often referred to as a
combination array or an array of arrays. Because maximum radiation occurs
at right angles to the plane of the array, the term broadside array is also
used.
4-103. The front-to-back ratio is the ratio of the energy radiated in the
principal direction compared to the energy radiated in the opposite direction
for a given antenna.
4-104. Various reflected and refracted components of the propagated wave
create effects of reinforcement and cancellation. At certain distant points
from the transmitter, some of the wave components meet in space. Reception
at these points is either impaired or improved. If the different components
arrive at a given point in the same phase, they add, making a stronger signal
available. If they arrive out of phase, they cancel, reducing the signal
strength.
Radiation Pattern
4-105. Effects similar to those described in the preceding paragraph can be
produced at the transmitting point itself. Consider the antennas shown in
figure 4-22, views A and B. View A shows an unobstructed view of the
radiation pattern of a single dipole. In view B, two dipoles, shown as points 1
and 2, are perpendicular to the plane of the page. They are spaced one-
quarter wavelength apart at the operating frequency. The radiation pattern
from either antenna 1 or 2, operating alone, would be uniform in all
directions in this plane, as shown in view A. Suppose that current is being fed
to both antennas from the same transmitter in such a way that the current
fed to antenna 2 lags the current in antenna 1 by 90 degrees. Energy
radiating from antenna 1 toward receiving location X will reach antenna 2
after one-quarter cycle of operation. The energy from both antennas will add,
and propagation toward X will be strong.
4-30
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