What are Wireless
Antennas?
Wireless antennas are the part of a radio communications
system that radiate and/or collect radio frequency energy. The
type of antenna used, will determine the path of radiation.
How are Wireless
Antennas used?
Wireless antennas are typically connected via low loss
coaxial cable either to an amplifier, splitter, filter or directly
to a wireless access point or router. For outdoor applications
wireless antennas are often attached via mounting clamps to a mast
or to the side of a building via mounting brackets. Wireless
Antennas used indoors are typically ceiling mounted or sometimes
mounted high up on a wall.
Where are Wireless
Antennas used?
Wireless antennas are used in many environments and for many
applications. Models for both indoor and outdoor use are available
as well as specialty antennas such as Marine antennas used in
nautical applications.
Wireless antennas are used in both commercial and
military/government applications including small office /home office
(SOHO) networks, Enterprise (office) networks, supervisory control
and data acquisition (SCADA) networks, homeland security, factory
automation, mining, oil processing , wireless cafe “hotspots”,
energy management and control, police, fire and emergency services
networks, radio frequency identification (RFID) applications, and
industrial science and medical (ISM) networks.
Wireless communication involves the transport of
voice, video and data using Radio Frequency (RF) or Microwaves.
Radio Frequency is defined as a rate of
oscillation or frequency within a range of approximately 3kHz to 300
GHz. Typical Radio Frequency applications include AM broadcasting,
navigational beacons, wireless networks, and shortwave radio.
Microwaves range from approximately between
300MHz and 300GHz and are typically used for broadcast television,
FM broadcasting, aviation communications, radar and satellite links.
Today’s business and some Government networks typically utilize the
2.4GHz-5.8GHz RF range which encompasses one or several of the IEEE
802.11a, b and g, n wireless standards. Other popular RF frequencies
used today include 900MHz for ISM (Industrial, Scientific and
Medical) RFID (Radio Frequency Identification) and 1.9GHz for PCS
(Personal Communication Service) applications
Indoor RF Wireless Network Information:
When dealing with the installation and expansion
of indoor wireless networks several factors must be considered. Most
manufacturers of wireless access points and routers indicate a
typical range that their equipment can provide. Usually these range
estimates require line of sight which means you will need a clear
unobstructed view of the antenna from the remote point in the link.
In most cases there will be obstacles present in an indoor
installation that could affect performance. Signals generally will
not penetrate metal or concrete walls. Other factors that will
reduce range and affect coverage area include metal studs in walls,
concrete fiberboard walls, aluminum siding, foil-backed insulation
in the walls or under the siding, pipes and electrical wiring,
furniture and sources of interference. Other sources include other
wireless equipment, cordless phones, microwave ovens, radio
transmitters and other electrical equipment. Due to the increased
gain, installing range extender antennas in the presence of
interference could actually yield equal or worse range.
In wireless transmissions, reflections (when
wireless signals “bounce” off objects) and multipath (when wireless
signals travel in multiple paths arriving at the receiver at
different times) are as important as signal strength in determining
the success of an installation. A signal will also exhibit peaks and
nulls in its amplitude and alteration of its polarization (vertical
or horizontal) when propagating through walls, ceilings and
reflecting off metallic objects.
Wireless radios have special hardware and
software to deal with multipath and signal level nulls, but if the
antenna is in a poor location, the radio will not be able to
communicate. When trying to get the best performance in a location
with a lot of barriers or reflections, it is important to be able to
move the antenna in all three axes in order to minimize the effects
of multipath and optimize the signal strength.
Outdoor RF Wireless Network Information:
Outdoor RF wireless network experience the same factors
such as reflections and multipath as Indoor networks. For outdoor
wireless installations clear line of sight is optimal. Trees and
leaves are obstructions to 802.11 frequencies so they will partially
or entirely block the signal if not cleared.
Before deploying any wireless network a site survey is recommended.
The site survey typically entails installing an access point at each
location where user groups are located and then monitoring the
wireless signal strength by walking varying distances away from the
access points using a laptop with site survey software. The result
will show you where out may need more access points to provide
sufficient coverage or where you may need to move an access point
for optimal wireless connectivity.
