Aviat Networks ECLIPSE EDGE, User Manual

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34 Aviat Networks
Chapter 3. Eclipse Edge Installation
Tracking Path Error for Edge Antennas
Side lobe signal readings can be confused with main beam readings. This is
particularly true for the first side lobe as the signal level at its center is greater than
the signal level at the edges of the main beam, and if tracking on an incorrect
elevation (or azimuth) a false impression of main beam reception can be obtained.
Figure 3-13
shows an example of this with a simplified head-on view of an antenna
radiation pattern, and tracking paths for three elevation settings.
Figure 3-13.
Example Tracking Path Signals
Such first side lobe peaking is probably the most frequent cause of misalignment in
both azimuth and elevation, especially so if one side lobe peaks higher than the other,
as shown in
Figure 3-14
, which represents a head-on view of azimuth and elevation
tracking paths centered on a higher first side lobe.
4 Peak of 1st side lobe, 20-25 dB below main peak.
5 Trough between first and second side lobes, 30 dB or more below main
peak.
6 Subsequent side lobe peaks and troughs.
Item Description
Item Description
1 Line AA represents the azimuth tracking path of a properly aligned
antenna. The main beam is at point 2, and the first side lobes at points 1
and 3.
2 Line BB represents the azimuth tracking path with the antenna tilted down
slightly. Signal strength readings show only the first side lobe peaks, 4
and 5. In some instances the side lobe peaks are unequal due to antenna
characteristics, which can lead to the larger peak being mistaken for the
main beam. The correct method for locating the main beam in this case is
to set the azimuth position midway between the first side lobe peaks, and
then adjust the elevation for maximum signal.
3 Line CC represents an azimuth tracking path with the antenna tilted down
further still. The first side lobe signal peaks (6 and 7) appear as one peak,
leading to a mistaken interpretation of a main beam. The correct method
for locating the main beam is to set the azimuth at mid peak, between 6
and 7, and then adjust elevation for maximum signal.
A
B
C C
B
A
6 77
1 2 3
4 5
6 7
4 5
1
22
3
C C
B B
A A
1
2
3