(1) The energy radiated by an antenna forms an electromagnetic field having a definite
pattern, depending on the type of antenna used. This pattern is used to show both range and directional
characteristics of an antenna. A vertical antenna theoretically radiates energy equally in all directions.
In practice, however, the pattern is usually distorted by nearby obstructions or terrain features.
(2) The full radiation pattern is a three-dimensional field. It looks somewhat like a doughnut
with the transmitting antenna in the center (figure 15). Radiation patterns will change with the design of
the antenna. The virtually round doughnut shape is radiated by omni-directional antennas. Elongated
ellipses are formed by the directional VHF and UHF antennas. Narrow, highly concentrated beams are
associated with microwave and tropospheric signals in the UHF and SHF range. The elliptical and
narrow beam patterns permit the major portion of the energy to be concentrated in the direction of
transmission. This directional pattern is known as the lobe (figure 16).
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