Radwin 2000+ SERIES User Manual - page 225
RADWIN
2000+
Series
User
Manual
Release
4.2.40
19
‐
4
About
the
Fresnel
Zone
19.4
About
the
Fresnel
Zone
The
Fresnel
zone
is
an
elliptically
shaped
conical
zone
of
electromagnetic
energy
that
propagates
from
the
transmitting
antenna
to
the
receiving
antenna.
It
is
always
widest
in
the
middle
of
the
path
between
the
two
antennas.
Figure
19
‐
1:
Fresnel
zone
Fresnel
loss
is
the
path
loss
occurring
from
multi
‐
path
reflections
from
reflective
surfaces
such
as
water,
and
intervening
obstacles
such
as
buildings
or
mountain
peaks
within
the
Fresnel
zone.
Radio
links
should
be
designed
to
accommodate
obstructions
and
atmospheric
conditions,
weather
conditions,
large
bodies
of
water,
and
other
reflectors
and
absorbers
of
electromagnetic
energy.
The
Fresnel
zone
provides
us
with
a
way
to
calculate
the
amount
of
clearance
that
a
wireless
wave
needs
from
an
obstacle
to
ensure
that
the
obstacle
does
not
attenuate
the
signal.
There
are
infinitely
many
Fresnel
zones
located
coaxially
around
the
center
of
the
direct
wave.
The
outer
boundary
of
the
first
Fresnel
zone
is
defined
as
the
combined
path
length
of
all
paths,
which
are
half
wavelength
(1/2
)
of
the
frequency
transmitted
longer
than
the
direct
path.
If
the
total
path
distance
is
one
wavelength
(1
)
longer
than
the
direct
path,
then
the
outer
boundary
is
said
to
be
two
Fresnel
zones.
Odd
number
Fresnel
zones
reinforce
the
direct
wave
path
signal;
even
number
Fresnel
zones
cancel
the
direct
wave
path
signal.
The
amount
of
the
Fresnel
zone
clearance
is
determined
by
the
wavelength
of
the
signal,
the
path
length,
and
the
distance
to
the
obstacle.
For
reliability,
point
‐
to
‐
point
links
are
designed
to
have
at
least
60%
of
the
first
Fresnel
zone
clear
to
avoid
significant
attenuation.