Locating Horizon; Near Field Effects; Compact Plus Systems; Table 9-1 System Height Vso - DragonWave Horizon COMPACT Plus Product Manual

9.0 Locating Horizon Compact Plus Systems
For both licensed and unlicensed systems, their location, relative to nearby obstacles, is an important
factor to consider when planning an installation. For systems mounted on buildings, roof edges and
parapets, the roof surface itself, air conditioning plant, other antenna systems, walls and overhead objects
are all considered potential obstacles. On tower mounted systems you must consider the proximity of
other antenna systems and mounting hardware.
You must also ensure that there is a clear line of sight (LOS) between the antennas of a Horizon
Compact Plus system link.
9.1

Near Field Effects

Near field effects, resulting from a number of minor radiation lobes normally found around antenna
systems, can reflect off nearby objects and interfere with the normal reception of the radio. Reflected
waves can also change their polarization. This is especially important for cross polarized LMDS and
unlicensed systems.
Consider an LMDS system or an unlicensed installation that transmits with vertical polarization and
receives with horizontal polarization. If the near field vertically polarized transmitted signal reflects off an
obstacle located too close to the antenna system, then the reflected signal changes its polarization to
horizontal, which is the same polarization as the receiver. This causes the receiver to "swallow" the
transmitted signal, resulting in receiver "swamping", excessive noise and the inability to receive the signal
from the far end of the link. Ensuring that obstacles and objects are not too close to the antenna system
will avoid this problem.
As a "rule of thumb", for both co-polarized and cross-polarized installations, ensure that you maintain an
angle of 45 degrees, or greater, between the far side of the highest part of an obstacle and the underside
of the dish/reflector. The diagrams in Figure 9-1 illustrate this approach. Also, remember to apply this rule
in all directions around the radio, above, below and to each side. An exception to this rule can be applied
when the system is positioned 12.5 m (40 ft) or more from the edge of a roof clear of obstacles (a roof
edge is considered an obstacle). In this case the system need not be higher than 2.5 m (8 ft) above the
roof surface.
Table 9-1 shows the minimum antenna height requirements above obstacles for the 24 GHz Unlicensed
frequency band.
Table 9-1 System Height vs Obstacle Distance for 24 GHz Unlicensed
Distance from 0 30
Obstacle in cm (ft)
(0) (1)
Minimum System
30 60
Height above
(1) (2)
Obstacle in cm (ft)
Horizon Compact Plus Release 1.0.1
60 90 120 150 180
(2) (3) (4) (5) (6)
90 120 131 134 137
(3) (4) (4.36) (4.46) (4.55)
210 240 270 300
(7) (8) (9) (10)
139 142 145 147
(4.64) (4.73) (4.82) (4.91)
Wireless Ethernet Product User Manual – Volume 1
600 900 1200 >1200
(20) (30) (40) (>40)
175 202 229 240
(5.82) (6.73) (7.64) (8)