Aruba AP-85, Руководство по установке

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Aruba AP-85 Outdoor Access Point Series | Installation Guide Understanding Antennas | 35
Now, still using the same ball with the same available surface area, how would you be able to stretch the ball farther out?
One way is to press down on the top of the ball and squash it down vertically. This would keep the same basic shape in the
horizontal plane (round), but it would force the ball to stretch, creating a pancake shape, in the vertical direction (see
Figure
25 ). This represents the concept of the high gain omni-directional antenna, which achieves a greater coverage distance in the
horizontal direction at the expense of coverage in the vertical areas of the radiating sphere.
Figure 25 High Gain Omni-Directional Antenna
To stretch the ball primarily in one direction (instead of in all directions), push the ball, both vertically and horizontally, on
the sides and on the back, to force the ball to deform in a single direction. This action would significantly distort the shape of
the original ball both horizontally and vertically, but it will allow you to stretch the same ball a lot farther in one direction
(see
Figure 26 ). This represents the concept of the high gain directional antenna, which is designed to compress the entire
radiating sphere into a single predominate direction.
Figure 26 High Gain Directional Antenna
N O T E
Gain is created by forcing transmitted power to radiate in a preferred direction rather than radiating
in all directions of an ideal sphere. Therefore, a high gain signal is always accompanied by loss of
available signal in some other portion of the ideal sphere. High gain directional antennas are ideal for
sites requiring directed coverage in a specific area or extended range for bridging applications, but
they are not suited for sites requiring uniform coverage in large areas. It is important to keep in mind
that both vertical and horizontal coverage can be affected by the use of a higher gain antenna and
beamwidth (a measure of coverage) is always inversely related to gain.
High Gain
Omni-Directional Antenna
Compressed vertical signal,
which expands signal
horizontally
High Gain Directional Antenna
Entire sphere compressed into a
single predominate direction, focusing
RF energy to a targeted area of
coverage