4-19
maximum at the center and minimum at the ends. Voltage is minimum at the center and maximum at the
ends, as was shown in figure 4-6.
Radiation Patterns
In the following discussion, the term DIPOLE is used to mean the basic half-wave antenna. The term
DOUBLET is used to indicate an antenna that is very short compared with the wavelength of the
operating frequency. Physically, it has the same shape as the dipole.
RADIATION PATTERN OF A DOUBLET.—The doublet is the simplest form of a practical
antenna. Its radiation pattern can be plotted like the radiation pattern of the flashlight (fig. 4-12). Figure
4-14 shows the development of vertical and horizontal patterns for a doublet. This in NOT a picture of the
radiation, but three-dimensional views of the pattern itself. In three views the pattern resembles a
doughnut. From the dimensions in these views, two types of polar-coordinate patterns can be drawn,
horizontal and vertical. The HORIZONTAL PATTERN view A is derived from the solid pattern view C
by slicing it horizontally. This produces view B, which is converted to the polar coordinates seen in view
A. The horizontal pattern illustrates that the radiation is constant in any direction along the horizontal
plane.
Figure 4-14.—Development of vertical and horizontal patterns.
A VERTICAL PATTERN view E is obtained from the drawing of the vertical plane view D of the
radiation pattern view C. The radiation pattern view C is sliced in half along a vertical plane through the
antenna. This produces the vertical plane pattern in view D. Note how the vertical plane in view D of the
radiation pattern differs from the horizontal plane in view B. The vertical pattern view E exhibits two
lobes and two nulls. The difference between the two patterns is caused by two facts: (1) no radiation is
