_______________________________________________________________________ Antennas
As more elements are added, the effect is heightened, as shown in view C.
Unimportant minor lobes are generated as more elements are added.
Figure 4-26. Single Half-Wave Antenna versus Two Half-Wave Antenna in Phase
4-118. More than four elements are seldom used because accumulated losses
cause the elements farther from the point of feeding to have less current than
the nearer ones. This introduces an unbalanced condition in the system and
impairs its efficiency. Space limitations often are another reason for
restricting the number of elements. Because this type of array is in a single
line, rather than in a vertically stacked arrangement, the use of too many
elements results in an antenna several wavelengths long.
4-119. Radiation pattern. The characteristic radiation pattern of a given
array is obtained at the frequency or band of frequencies at which the system
is resonant. The gain and directivity characteristics are lost when the
antenna is not used at or near this frequency and the array tunes too sharply.
A collinear antenna is more effective than an end-fire array when used off its
tuned frequency. This feature is considered when transmission or reception is
to be over a wide frequency band. When more than two elements are used,
this advantage largely disappears.
4-35
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