User Guide: Technical Reference
SECTION 2
ioLink 4
SYSTEM COMPONENTS
PRELIMINARY
Customer Support (202) 333-7031
2-7
2.6.2 Polarization
Another important antenna characteristic is polarization. Polarization refers to the direction in which
the electrical field (i.e., wave) of a signal is oriented. For example, antennas may have linear,
elliptical, or circular polarization. The antenna at each end of the link must have the same type of
polarization, and they must be oriented in the same direction (e.g., horizontal to horizontal or right-
hand circular to right hand circular). Linearly polarized antennas are the most common type used with
this kind of system. Most often, linearly polarized antennas are oriented either horizontally or
vertically. Antennas with circular or elliptical polarization have their signal constantly rotating either
clockwise or counter-clockwise (commonly called right-handed or left-handed). The advantage of this
is that it helps to eliminate multi-path fading due to the nature of circular polarization rejection. The
degree to which “the other” polarization is ignored is called “cross polarization rejection.” This can be
used to an advantage, allowing parallel installation of
ioLink 4
links (e.g., a horizontal link and a
vertical link).
Multipath fading is a situation in which the signal reflects off some object (typically the ground or a
building) and causes interference at the receiving antenna. The rejected, multipath signal travels
farther so it is slightly delayed from the main signal. If the “true” signal and the reflected signal reach
the antenna out of phase, the reflected signal will destructively interfere with the “true” signal. When
linearly polarized signals reflect off an object they retain their orientation, but when signals with circular
polarization reflect off an object their polarization is reversed (i.e., left-handed becomes right-handed
and vice versa). It is for this reason that circular polarization is more effective at eliminating multi-path
fading and recommended under certain conditions. The destructive cancellation of multipath is highly
frequency specific; so, broadband spread spectrum systems such as
ioLink 4
are inherently multipath
tolerant. Installation in severe multipath areas may however benefit from the use of circular
polarization.
Note:
Antenna sizes and their corresponding distances from each other should be calculated for
each individual path.
ioWave
’s System Integration team can make accurate recommendations
for the antenna once the sites for the link have been determined.
2.7
Typical Link Setup
