Table of Contents
Advertisement
Antenna gain is sometimes specified in dBi, which is how much the antenna increases the signal power
compared to using an isotropic antenna. An isotropic antenna is a theoretical perfect antenna that sends
out radio signals equally well in all directions. dBi represents the true gain that the antenna provides.
Types of Antennas For WLAN
There are two types of antennas used for wireless LAN applications.
Omni-directional antennas send the RF signal out in all directions on a horizontal plane. The
coverage area is torus-shaped (like a donut) which makes these antennas ideal for a room
environment. With a wide coverage area, it is possible to make circular overlapping coverage areas
with multiple access points.
Directional antennas concentrate the RF signal in a beam, like a flashlight. The angle of the beam
width determines the direction of the coverage pattern; typically ranges from 20 degrees (less
directional) to 90 degrees (very directional). The directional antennas are ideal for hallways and
outdoor point-to-point applications.
Antenna Polarization
The orientation of the antenna will change the orientation of the signal. The transmitting and receiving
antennas should be both polarized either horizontally or vertically. Adjacent antennas on different
frequencies can be cross-polarized to help reduce interference between the two, if your operating license
permits this.
Towers
When planning antenna placement, it might be necessary to build a freestanding tower for the antenna.
Regulations and limitations define the height and location of these towers with respect to airports, runways,
and airplane approach paths. The Federal Aviation Administration (FAA) controls these regulations. In
some circumstances, the FAA, the FCC, or both, must approve the tower installations.
To ensure compliance, review the current FCC regulations regarding antenna structures. These regulations
(along with examples) can be viewed on the FCC web site at http://www.fcc.gov/antenna/.
Path Planning
To get the most value from a wireless system, path planning is essential. In addition to the fact that radio
signals dissipate as they travel, many other factors operate on a microwave signal as it moves through
space. All of these must be taken into account, to avoid attenuation of the signal by path obstruction.
Calculating a Link Budget
A link budget is a rough calculation of all known elements of the link, to determine if the signal will have
the proper strength when it reaches the other end of the link.
To make this calculation, consider the following information.
Site Planning
ZyAIR B-5000 User's Guide
A-5
Advertisement
Table of Contents
