Visual and RF Line-of-Sight ( LOS ) between the sending and receiving
antennas is essential in achieving long range in wireless communication
systems. There are two types of LOS that are generally used to describe an
Visual LOS is the ability to see from one site to the other. It requires only a
straight liner path between two points.
RF LOS requires not only visual LOS, but also a football-shaped path free of
obstacles for data to optimally travel from one point to another.
The Fresnel Zone can be thought of as a football-shaped tunnel between two
sites that provides a path for RF signals.
In order to achieve the greatest range, the football-shaped path in which radio
waves travel must be free of obstructions. Buildings, trees or any other
obstacles in the path will decrease the communication range. If the antennas
are mounted just barely off the ground, over half of the Fresnel zone ends up
being obstructed by the earth resulting in significant reduction in range. To
avoid this problem, the antenna should be mounted high enough off of the
ground so that the earth does not interfere with the central radius of the