Practical_Antenna_Handbook_0071639586

Wire 2
C h a p t e r 1 0 : W i r e A r r a y s 259
Wire 1
2
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Resultant
pattern
Direction
of
maximum
reception
Figure 10.7 Radiation pattern of vee beam antenna consists of the algebraic sum of the two longwire
patterns that make up the antenna.
The unterminated vee beam of Fig. 10.7 has a bidirectional pattern that is created by
summing together the patterns of the two individual wires. Proper alignment of the
main lobes of the two wires requires an included angle, between the wires, of twice the
radiation angle of each wire. If the radiation angle of the wire is b, then the appropriate
included angle is 2b. To raise the pattern a few degrees, the 2b angle should be slightly
less than these values. It is common practice to design a vee beam for a low frequency
(e.g., 75-/80- or 40-m bands), and then to also use it on higher frequencies that are harmonics
of the minimum design frequency. A typical vee beam works well over a very
wide frequency range only if the included angle is adjusted to a reasonable compromise.
It is common practice to use an included angle that is between 35 and 90 degrees, depending
on how many harmonic bands are required.
Vee beam patterns are usually based on an antenna height that is greater than a halfwavelength
from the ground. At low frequencies, such heights may not be possible, and
you must expect a certain distortion of the pattern because of ground reflection effects.