Cabletron Systems RoamAbout 802.11 Supplementary Manual - The Fresnel Zone
Site Preparation Guide
6
Required Data for Antenna Installation Company
The Fresnel Zone
You need a clear line-of-sight between antennas to set up an outdoor installation that
meets your requirements in terms of range and throughput performance.
The shape of the radio beam, also defined as the Fresnel Zone, is bulged in the middle.
The exact shape and width of the Fresnel Zone is determined by the path length and
frequency of the radio signal.
If any significant part of the Fresnel Zone is obstructed, a portion of radio energy is
lost, resulting in reduced performance. For optimal performance, you must ensure that
the antenna products you choose, in combination with the height of the antenna
installation above ground, will provide sufficient clearance to allow your antenna
installation to cover the distance between the two wireless sites.
As shown in Figure 4, there are two major variables that determine the shape of the
Fresnel Zone:
•
The distance between the antennas (1).
•
The minimum clearance required for optimal performance (2).
NOTE
A
wireless outdoor antenna installation that lacks sufficient
clearance will suffer from poor performance. When radio
performance is poor, the network response is poor as well, due to
many retransmission attempts of lost data frames.