I-O Wireless WBC11, Руководство пользователя

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2.1.2 Multi path
2.1.2.1 Polarization
Direct Sequence technology is more sensitive for multi-path effects than the
traditional Frequency Hopping. Multi-path effects can be explained as coherent
signals (signals from the same source) arriving at the antenna at different times
due to the difference in path length. Several signals from the same source
meeting at the receiving antenna can arrive in phase, out of phase or in between.
When the level of each incoming signal is included, the effects can be any of the
following:
Level Phase Result
Equal In Strong reception
Unequal In Good results
Equal Out Possible loss of
reception
Random Random Variable levels
The conductivity of the reflector and polarization of the wave before reflection
primarily affect the level of the signal. Horizontal polarized signals, which are
parallel to the reflecting surface, will reflect almost totally without appreciable loss
at the point of bounce.
Vertically polarized signals are perpendicular to the reflecting surface, and will
either be totally reflected from a conductor, or will propagate along the surface
(depending on the angle of the arriving energy). Since radiated waves penetrate
loose materials, energy can be lost to heat generation.
Circularly polarized signals are composed of a combination of vertically and
horizontally polarized signal which are in phase quadrature (offset 90
°
) with each
other. Depending on their phasing, the sense of circularly polarized signals are
described as right-handed or left-handed. Circularly polarized signals have the
unique property that the sense changes upon reflection. Thus, a right-hand
circularly polarized signal becomes left-handed upon reflection. A circularly
polarized antenna will only respond to one sense, either right or left, depending
on its design.
By using circular polarization, the effect of multipath interference can be greatly
reduced. This makes setting up wireless links easier and more reliable than
when using horizontal or vertical polarization. I-O bridge products use circularly
polarized antennas exclusively.
2.1.2.2 Refraction