AvMesh
®
RF Communications Systems
Installation & Service Manual
Latest products and information available at
www.avlite.com
11
An electromagnetic wave is made up of an electric field and magnetic field that oscillate
perpendicular to each other. Polarization of the electromagnetic waves refers to the plane
in which the electric field is oscillating. Although there are many forms of polarization, the
electric field is often polarized in either the vertical direction or in the horizontal direction
and this is dependent on the antenna orientation in relation to the earth.
Similar to electromagnetic wave polarization, the most common forms of antenna
polarization are vertical and horizontal. A vertically polarized antenna transmits and
receives vertically polarized signals best whereas a horizontally polarized antenna
transmits and receives horizontally polarized signals best. Antenna polarization is an
important factor to consider as antennas are most effective when they are polarized in the
same direction as the received electromagnetic waves (signals). If the polarization of the
antenna and received signal do not match, a corresponding decrease in the received signal
level will occur.
Once a signal has been transmitted, its polarization should remain the same. However,
reflections, refractions and diffractions occurring between the receiver and transmitter
can slightly change the polarization of the signal and this has the potential to degrade the
received signal level.
Figure 7:
Vertically (left) and Horizontally (right) polarized antennas
The way in which radio waves (signals) travel from one point to another is called RF
propagation and is an essential aspect of how radio communications systems operate (i.e.
how the radio signals travel from the transmitter to the receiver). RF propagation is greatly
affected by the environment in which the radio waves travel as well as the various objects
that may appear in the transmission path. It is the transmission path that governs the level
and quality of the received signal.
There are a number of categories into which RF propagation can be placed and these are
dependent on the frequency of radio waves involved in the radio communications system.
A brief description of the main categories of RF propagation are shown below.
Avlite products (2.4 GHz) operate at frequencies in the Ultra high frequency (UHF) range
of the radio spectrum. The main type of RF propagation in this frequency range is line-of-
sight propagation.
3.5 RF Propagation
3.4.3 Polarization
