4-41
LONG-WIRE ANTENNA
A LONG-WIRE ANTENNA is an antenna that is a wavelength or longer at the operating frequency.
In general, the gain achieved with long-wire antennas is not as great as the gain obtained from the
multielement arrays studied in the previous section. But the long-wire antenna has advantages of its own.
The construction of long-wire antennas is simple, both electrically and mechanically, with no particularly
critical dimensions or adjustments. The long-wire antenna will work well and give satisfactory gain and
directivity over a frequency range up to twice the value for which it was cut. In addition, it will accept
power and radiate it efficiently on any frequency for which its overall length is not less than
approximately 1/2 wavelength. Another factor is that long-wire antennas have directional patterns that are
sharp in both the horizontal and vertical planes. Also, they tend to concentrate the radiation at the low
vertical angles. Another type of long-wire antenna is the BEVERAGE ANTENNA, also called a WAVE
ANTENNA. It is a horizontal, long-wire antenna designed especially for the reception and transmission
of low-frequency, vertically polarized ground waves. It consists of a single wire, two or more
wavelengths long, supported 3 to 6 meters above the ground, and terminated in its characteristic
impedance, as shown in figure 4-34.
Figure 4-34.—Beverage antenna.
Q44. To radiate power efficiently, a long-wire antenna must have what minimum overall length?
Q45. What is another name for the Beverage antenna?
V ANTENNA
A V ANTENNA is a bi-directional antenna used widely in military and commercial
communications. It consists of two conductors arranged to form a V. Each conductor is fed with currents
of opposite polarity.
The V is formed at such an angle that the main lobes reinforce along the line bisecting the V and
make a very effective directional antenna (see figure 4-35). Connecting the two-wire feed line to the apex
of the V and exciting the two sides of the V 180 degrees out of phase cause the lobes to add along the line
of the bisector and to cancel in other directions, as shown in figure 4-36. The lobes are designated 1, 2, 3,
and 4 on leg AA', and 5, 6, 7, and 8 on leg BB'. When the proper angle between AA' and BB' is chosen,
lobes 1 and 4 have the same direction and combine with lobes 7 and 6, respectively. This combination of
two major lobes from each leg results in the formation of two stronger lobes, which lie along an
imaginary line bisecting the enclosed angle. Lobes 2, 3, 5, and 8 tend to cancel each other, as do the
smaller lobes, which are approximately at right angles to the wire legs of the V. The resultant waveform
pattern is shown at the right of the V antenna in figure 4-36.
