LightPointe AireLink 60, Инструкция по установке и эксплуатации

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AireLink
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60 Installation and User Manual Rev. D System Installation
Page 63
5.7 ANTENNA RADIATION PATTERN AND SIDE LOBES
When aligning a 60 GHz radio with a narrow beam directional antenna pattern, it is important to
understand that besides the “antenna main lobe” that contains most of the energy, there are also
“antenna side lobes”. A “perfect” antenna would contain all energy in the main lobe but this is
physically impossible. Although these side lobes contain far less energy - in the case of a good
directional 60 GHz antenna the power of the 1
st side lobe is typically more than 20 dB lower when
compared to the main lobe’s peak power - one can “see” the 1 st side lobe during the alignment process.
This is mainly because in a 60 GHz antenna the main lobe and the 1 st antenna side lobe are separated
by an angle of just 2-3 degrees. This small value for the angular separation is actually close to the
radiation angle of the main lobe itself. When installing a millimeter wave radio transmission system it
is important to keep in mind that the antenna main lobe and the 1
st antenna side lobe point in virtually
the same direction. Aligning the system on a side lobe instead of aligning it on the main lobe will
negatively impact performance of the system. For illustrative purposes Fig. 5-9 shows a typical antenna
Radiation Pattern Envelope (RPE) diagram of a Cassegrain antenna.
Note:
During the alignment process it is important to find the main lobe and not to align
the system on a side. To ensure that the main lobe is found, move the system
about 10 degrees in horizontal and vertical direction and away from the
perceived highest readout voltage. While “scanning” through the beam pattern
from the left to the right (or from the top to the bottom) one can find the higher
RSSI voltage readings before the signal drops significantly. These two “local”
voltage maxima to the left and the right of the main lobe are the 1
st side lobe.
Figure 5-4: Typical antenna Radiation Pattern Envelope (RPE) diagram