
Time
Domain
Antenna
Transmission
Measurements
Time
Domain
Antenna
Transmission
Measurements
Time
Domain
is
also
useful
when
making
antenna
transmission
measurements
and
characterizing
the
antenna
test
range
for
multipath
signals
.
Time
Domain
concepts
are
very
similar
between
Radar
Cross
Section
measurements
and
antenna
transmission
measurements
.
This
portion
of
the
manual
will
cover
only
those
areas
that
are
unique
to
antenna
transmission
measurements
.
Please
refer
to
the
section
on
Time
Domain
RCS
Measurements
for
additional
detail
on
Time
Domain
measurements
.
Time
Domain
Characterization
of
Antenna
Range
Multipath
Antenna
range
multipath
describes
signals
received
by
the
test
antenna
from
directions
other
than
line-of-sight
from
the
transmitter
.
The
dominant
sources
of
multipath
responses
occurring
in
outdoor
ranges
are
the:
Responses
caused
by
direction
illumination
of
the
ground.
Energy
reecting
from
nearby
buildings
or
other
objects
.
F
or
indoor
ranges
,
multipath
can
be
caused
by:
Reections
from
non-ideal
absorber
material
Direct
illumination
from
the
feed
antenna
of
a
compact
antenna
test
range
(CA
TR)
to
the
test
antenna.
Scattering
o
of
CA
TR
reectors
Re-radiation
of
the
receive
antenna
that
illuminates
close-in
obstacles
and
causes
secondary
responses
.
These
multipath
responses
arrive
in
parallel
with
the
main
line-of-sight
response
.
Because
the
reception
of
multipath
depends
on
the
radiation
pattern
of
the
antenna
and
its
orientation,
the
resulting
errors
are
not
stationary
and
there
is
no
simple
mathematical
technique
to
characterize
and
remove
them.
However
,
Time
Domain
analysis
of
the
test
range
can
help
to
determine
their
levels
,
which
can
help
in
the
placement
of
absorber
or
other
structures
to
reduce
their
reception
by
the
test
antenna.
Antenna
range
geometry
is
a
signicant
factor
when
attempting
to
distinguish
Time
Domain
transmission
responses
.
The
dierence
in
the
main
path
and
ground
path
can
be
determined
using
the
following
formula
(for
equal
antenna
heights
and
a
at
ground
contour).
The
dierence
between
these
two
paths
on
a
conventional
outdoor
range
depends
on
the
height
(H)
of
the
antennas
above
ground
and
the
distance
(D)
between
the
transmit
and
receive
antennas
.
1
=
(Square
Root
(D
2
+
(2H)
2
))
0
D
Usually
,
higher
antennas
or
shorter
distance
between
transmit
and
receive
towers
cause
a
greater
dierence
between
the
direct
and
ground
path
responses
.
Antenna
Impulse
Response
The
following
concepts
are
important
to
understand
in
interpreting
the
measured
antenna
transmission
Time
Domain
responses
.
F
ormulas
for
determining
the
Time
Domain
impulse
width
and
impulse
shape
are
the
same
as
given
in
T
able
13-1 ,
in
the
RCS
Time
Domain
section.
However
,
due
to
the
dispersion
and
to
internal
reections
,
many
antennas
have
Time
Domain
response
that
extends
longer
in
time
than
would
be
expected,
as
shown
in
Figure
13-13.
Introduction
to
Time
Domain
RCS
and
Antenna
Measurements
13-21
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