Adtran TRC6320 Manual Do Utilizador
Section 2 Microwave Path Engineering Basics
TRACER 6000 Series Split System Manual
24
Copyright © 2005 ADTRAN, Inc.
612806320L1-1A
Figure 2. Typical Antenna Beam Pattern
Antennas are also designed to radiate RF energy efficiently for a specific range of frequencies. Please
consult the data sheet for your particular antenna make and model to ensure that it is specified to operate in
the 5725 MHz to 5850 MHz frequency band for the TRACER 6320 system.
consult the data sheet for your particular antenna make and model to ensure that it is specified to operate in
the 5725 MHz to 5850 MHz frequency band for the TRACER 6320 system.
Fresnel Zones, Earth Curvature, and Antenna Heights
Fresnel zones correspond to regions in the microwave path where reflections of the intended signal occur
and combine in both constructive and destructive manners with the main signal, thereby either enhancing
or reducing the net power at the receiver.
and combine in both constructive and destructive manners with the main signal, thereby either enhancing
or reducing the net power at the receiver.
In general, the odd numbered Fresnel zones (1, 3, 5, ...) add constructively at the receiver, while the even
numbered Fresnel zones (2, 4, 6, ...) add destructively at the receiver.
numbered Fresnel zones (2, 4, 6, ...) add destructively at the receiver.
The first Fresnel zone corresponds to the main lobe, 60 percent of which must be free of physical
obstructions for the path calculations to be valid. Since the main lobe contains the vast majority of the
microwave energy, this zone is typically used to determine proper antenna heights when placing antennas
on towers or buildings.
obstructions for the path calculations to be valid. Since the main lobe contains the vast majority of the
microwave energy, this zone is typically used to determine proper antenna heights when placing antennas
on towers or buildings.
The curvature of the Earth becomes a legitimate obstruction for path lengths of 7 miles (11.26 kilometers)
or greater, and must also be accounted for when determining minimum antenna heights.
or greater, and must also be accounted for when determining minimum antenna heights.
The aggregate expression for minimum antenna height that incorporates both the 60 percent first Fresnel
zone and the Earth’s curvature is given by
zone and the Earth’s curvature is given by
where f is in GHz and d is in miles, or
where f is in GHz and d is in kilometers.
The minimum antenna heights for given path lengths are displayed in Table 7 on page 25 (feet/miles) and
Table 8 on page 25 (meters/kilometers).
Table 8 on page 25 (meters/kilometers).
main lobe
side lobes
h
72.1
d
4f
-----
0.125d
2
+
=
(feet)
h
21.975
d
6.436
f
-------------
0.0147d
2
+
=
(meters)