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Line of Sight
The shape of the radio beam, defined as the Fresnel Zone, is widest in the middle. The Fresnel
Zone is shown as the gray area between the antennas in
the Fresnel Zone is determined by the distance between the antenna and frequency of the radio
signal.
The radius of the radio beam, shown as the lower half of the Fresnel Zone, is the distance from the
center of the beam outward in any direction. The length of the radius is not based on the data rate
and the type of antenna.
Figure 1-1
The radius can be calculated using the following formula:
Where
D = Distance between the antennas in kilometers
f = Frequency in GHz
60% of the Fresnel Zone has to be clear of obstructions in order to be line of sight. In addition to
the Fresnel Zone height requirement, earth curvature may become a factor in paths longer than 2
Km. The additional antenna height can be calculated using the following formula:
Where
D = Distance between the antennas in kilometers
H = Height required to overcome earth curvature
Table 1-7
on page 1-12 and
Fresnel Zone and Line of Sight Clearance
Table 1-8
on page 1-12 list typical antenna height requirements.
Enterasys Wireless External Antenna Site Preparation and Installation Guide 1-11
Figure
Total Distance
Radius
=
r
8.675 D f
2
H
=
D
51499
Determining the Antenna Locations
1-1. The exact shape and width of
ASP f
l
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