Important Factors; Antenna Radiation; Table 10-1 Antenna Gains And - DragonWave Horizon COMPACT Plus Product Manual

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10.2 Important Factors

When you prepare to align the radio antennas, you must consider three important factors:
1. the radiation patterns of dish antennas (main lobe and side lobes)
2. the need for a Clear Line of Sight (LoS) (see Section 0)
3. the sensitivity of the alignment adjustment
10.2.1 Antenna Radiation Patterns
Dish antennas radiate a primary signal (main lobe) and a number of secondary signals (side lobes). The
main lobe is the strongest. When you align the radios, you must make sure to align to the main lobe of the
signal. If you mistake the first side side lobe for the main lobe during installation, there can be a 20-30 dB
loss of signal strength. For example, if the Calculated RSL = -42 dB then the side lobe would be at
approximately -62 dB, or 20 dB lower than the calculated level.
Table 10-1 Antenna Gains and Beam Widths – Selected Frequencies
Antenna
Size
30 cm/12"
60 cm/24"
90 cm/36"
120 cm/48"
Although in most cases only the first two side lobes are detected, depending on dish antenna size and the
distance between sites, it may be possible to "see" several side lobes (see Figure 10-3).
It is wise to pan the full 35 degrees available with the antenna alignment adjustment to locate all the lobes
that may be present, so that the main lobe can be positively identified. As you pan through the signal, the
side lobes will show up as peaks in the receive signal level (RSL), each peak getting stronger as you
approach the main lobe. The main lobe will always be the strongest.
The size of the beamwidth for the Horizon Compact Plus systems is approximately 2 degrees. Two
degrees is approximately equivalent to a thumb's width when one's arm is fully extended. Align as closely
to the centre of the 2-degree beamwidth as possible. It takes very little adjustment to swing past the main
lobe, as can be seen in Figure 10-5. A beamwidth of 2 degrees is very narrow and alignment errors can
occur when you lock onto a side lobe instead of onto the main lobe. If you align to one of the side lobes,
your signal strength will be reduced. Make sure you align the system to the main lobe.
Note: Verify the RSL is within 2 – 4 dB of the calculated value.
Horizon Compact Plus Release 1.0.1
18 GHz Horizon
Beamwidth of Gain
main lobe dBi
(degrees, 3 dB)
3.0 degrees 34
2.0 degrees 38.6
1.3 degrees 42.0
1.0 degrees 44.5
23 GHz Horizon
Beamwidth of Gain
main lobe dBi
(degrees, 3 dB)
2.7 degrees 35.1
1.7 degrees 40.2
1.1 degrees 43.7
0.8 degrees 46.2
Wireless Ethernet Product User Manual – Volume 1