156
Networking Fundamentals
Flat Panel
The fl at panel is a directional-type antenna used for point-to-point links.
The main advantage of a fl at panel is the aesthetics. The antenna blends in well
with building architecture, and many times it is unnoticeable. However, the
disadvantage of a fl at panel antenna is the consideration of wind load. High wind
areas can catch the fl at panel design like a sail on a ship. Flat panels must be
rigidly supported to reduce the effects of wind.
Parabolic
The parabolic antenna is used for point-to-point links. It a directional-type
antenna typically constructed from a grid of rods or mesh wiring. The parabolic
antenna enhances reception by refl ecting incoming electromagnetic waves with
its curved surface to a horn at its center. When the parabolic antenna transmits
electromagnetic waves, the horn transmits the signal toward the curved surface
of the antenna. The curved surface refl ects the electromagnetic waves to produce
a beamlike pattern in the same way light is refl ected from the curved surface
of a fl ashlight to produce a beam of light. The parabolic antenna is constructed
as a simple, curved surface or in the shape of a dish. When it is constructed in
the shape of a dish, it is usually called a parabolic disk or simply dish antenna. The
parabolic antenna greatly amplifi es a weak radio wave signal when compared
with other antenna types.
Figure 4-8.
Yagi antenna
constructed inside
a metal tube. The
metal tube enhances
reception and
transmission. (Photo
reprinted with the
permission of PCTEL,
Maxrad Product
Group.)