<s>
3D	B-Algorithm
radar	I-Algorithm
provides	O
for	O
radar	B-Application
ranging	O
and	O
direction	O
in	O
three	O
dimensions	O
.	O
</s>
<s>
In	O
addition	O
to	O
range	O
,	O
the	O
more	O
common	O
two-dimensional	O
radar	B-Application
provides	O
only	O
azimuth	O
for	O
direction	O
,	O
whereas	O
the	O
3D	B-Algorithm
radar	I-Algorithm
also	O
provides	O
elevation	O
.	O
</s>
<s>
Applications	O
include	O
weather	B-Application
monitoring	I-Application
,	O
air	O
defense	O
,	O
and	O
surveillance	O
.	O
</s>
<s>
The	O
information	O
provided	O
by	O
3D	B-Algorithm
radar	I-Algorithm
has	O
long	O
been	O
required	O
,	O
particularly	O
for	O
air	O
defence	O
and	O
interception	O
.	O
</s>
<s>
Before	O
the	O
advent	O
of	O
single	O
unit	O
3D	B-Algorithm
radars	I-Algorithm
,	O
this	O
was	O
achieved	O
with	O
separate	O
search	O
radars	B-Application
(	O
giving	O
range	O
and	O
azimuth	O
)	O
and	O
separate	O
height	B-Algorithm
finding	I-Algorithm
radars	I-Algorithm
that	O
could	O
examine	O
a	O
target	O
to	O
determine	O
altitude	O
.	O
</s>
<s>
These	O
had	O
little	O
search	O
capability	O
,	O
so	O
were	O
directed	O
to	O
a	O
particular	O
azimuth	O
first	O
found	O
by	O
the	O
primary	O
search	O
radar	B-Application
.	O
</s>
<s>
Steered	O
beam	O
radars	B-Application
steer	O
a	O
narrow	O
beam	O
through	O
a	O
scan	O
pattern	O
to	O
build	O
a	O
3-D	O
picture	O
.	O
</s>
<s>
Examples	O
include	O
NEXRAD	B-Algorithm
Doppler	B-Application
weather	I-Application
radar	I-Application
(	O
which	O
uses	O
a	O
parabolic	O
dish	O
)	O
and	O
the	O
AN/SPY	O
-1	O
passive	B-Algorithm
electronically	I-Algorithm
scanned	I-Algorithm
array	I-Algorithm
radar	B-Application
employed	O
by	O
the	O
Ticonderoga	O
class	O
of	O
guided	O
missile	O
cruisers	O
and	O
other	O
ships	O
so	O
equipped	O
with	O
the	O
Aegis	B-Application
Combat	I-Application
System	I-Application
.	O
</s>
<s>
Stacked	O
beam	O
radars	B-Application
emit	O
and/or	O
receive	O
multiple	O
beams	O
of	O
radio	O
waves	O
at	O
two	O
or	O
more	O
elevation	O
angles	O
.	O
</s>
<s>
An	O
example	O
of	O
a	O
stacked	O
beam	O
radar	B-Application
is	O
the	O
Air	O
Route	O
Surveillance	O
Radar	B-Application
.	O
</s>
