4-20
emitted from the ends of the doublet; and (2) maximum radiation comes from the doublet in a direction
perpendicular to the antenna axis. This type of radiation pattern is both NONDIRECTIONAL (in a
horizontal plane) and DIRECTIONAL (in a vertical plane).
From a practical viewpoint, the doublet antenna can be mounted either vertically or horizontally. The
doublet shown in figure 4-14 is mounted vertically, and the radiated energy spreads out about the antenna
in every direction in the horizontal plane. Since ordinarily the horizontal plane is the useful plane, this
arrangement is termed NONDIRECTIONAL. The directional characteristics of the antenna in other
planes is ignored. If the doublet were mounted horizontally, it would have the effect of turning the pattern
on edge, reversing the patterns given in figure 4-14. The antenna would then be directional in the
horizontal plane. The terms "directional" and "nondirectional" are used for convenience in describing
specific radiation patterns. A complete description always involves a figure in three dimensions, as in the
radiation pattern of figure 4-14.
Q17. What terms are often used to describe basic half-wave antennas?
Q18. If a basic half-wave antenna is mounted vertically, what type of radiation pattern will be
produced?
Q19. In which plane will the half-wave antenna be operating if it is mounted horizontally?
RADIATION PATTERN OF A DIPOLE.—The radiation pattern of a dipole (fig. 4-15) is similar
to that of the doublet (fig. 4-14). Increasing the length of the doublet to 1/2 wavelength has the effect of
flattening out the radiation pattern. The radiation pattern in the horizontal plane of a dipole is a larger
circle than that of the doublet. The vertical-radiation pattern lobes are no longer circular. They are
flattened out and the radiation intensity is greater.
Figure 4-15.—Radiation pattern of a dipole.
