Figure 4-40.Stacked turnstile antennas.
A vertical quarter-wave antenna several wavelengths above ground produces a high angle of
radiation that is very undesirable at vhf and uhf frequencies. The most common means of producing a low
angle of radiation from such an antenna is to work the radiator against a simulated ground called a
GROUND PLANE. A simulated ground may be made from a large metal sheet or several wires or rods
radiating from the base of the radiator. An antenna so constructed is known as a GROUND-PLANE
ANTENNA. Two ground-plane antennas are shown in figure 4-41, views A and B.
Figure 4-41.Ground-plane antennas.
When a unidirectional radiation pattern is desired, it can be obtained by the use of a corner reflector
with a half-wave dipole. A CORNER-REFLECTOR ANTENNA is a half-wave radiator with a reflector.
The reflector consists of two flat metal surfaces meeting at an angle immediately behind the radiator. In
other words, the radiator is set in the plane of a line bisecting the corner angle formed by the reflector