User's Manual

48
2.1.1. Polarization
Antenna polarization is another property which the installer must bear in mind especially in
an environment with few obstacles.
A radio wave travelling in free space contains an electric field pointing in a perpendicular
direction to that of the propagation. The orientation of this electric field in the antenna’s main
beam is referred to as the antenna polarization. The electric field is described as either linear
or circular which means that the field is either orientated along a single axis or rotating as the
radio wave passes a point in space.
The Eagle is linearly polarized in the direction of its height and in order to achieve the
maximum range it must be orientated in the same direction as the polarization of the incident
radio wave. It is important to note that due to the prevalence of conductive surfaces in a
typical industrial environment, the incident radio wave polarization is likely not to be as the
purely polarized as the wave emitted in the Gateway antenna. This randomizing of the
polarization due to the interaction with conductive structures is why a good signal strength is
practically always achieved within 30m regardless of the Eagle orientation.
Never-the-less, being cognizant of the effect of polarization is very important and changing
either the Eagle or Gateway’s antenna polarization is one of the tricks discussed later in
order to improve the signal for hard to reach Eagle. The table below lists the signal loss due
to a mismatch in polarization.
Incident Wave Polarization
Eagle Orientation
Offset
Polarization Mismatch
Loss
Linear
0°
0dB
Linear
180°
0dB
Linear
45°
3dB
Linear
90°
∞
Circular Left-Hand
Any Direction
3dB
Circular Right-Hand
Any Direction
3dB
Omnidirectional
Panel antenna
Sector antenna