<s>
Monopulse	B-Algorithm
radar	I-Algorithm
is	O
a	O
radar	B-Application
system	I-Application
that	O
uses	O
additional	O
encoding	O
of	O
the	O
radio	O
signal	O
to	O
provide	O
accurate	O
directional	O
information	O
.	O
</s>
<s>
Monopulse	B-Algorithm
radar	I-Algorithm
avoids	O
problems	O
seen	O
in	O
conical	B-Algorithm
scanning	I-Algorithm
radar	B-Application
systems	I-Application
,	O
which	O
can	O
be	O
confused	O
by	O
rapid	O
changes	O
in	O
signal	O
strength	O
.	O
</s>
<s>
Most	O
radars	B-Application
designed	O
since	O
the	O
1960s	O
are	O
monopulse	B-Algorithm
systems	O
.	O
</s>
<s>
The	O
monopulse	B-Algorithm
method	O
is	O
also	O
used	O
in	O
passive	O
systems	O
,	O
such	O
as	O
electronic	O
support	O
measures	O
and	O
radio	O
astronomy	O
.	O
</s>
<s>
Monopulse	B-Algorithm
radar	I-Algorithm
systems	O
can	O
be	O
constructed	O
with	O
reflector	O
antennas	O
,	O
lens	O
antennas	O
or	O
array	B-Algorithm
antennas	I-Algorithm
.	O
</s>
<s>
Historically	O
,	O
monopulse	B-Algorithm
systems	O
have	O
been	O
classified	O
as	O
either	O
phase-comparison	B-Algorithm
monopulse	I-Algorithm
or	O
amplitude	B-Algorithm
monopulse	I-Algorithm
.	O
</s>
<s>
Modern	O
systems	O
determine	O
the	O
direction	O
from	O
the	O
monopulse	B-Algorithm
ratio	O
,	O
which	O
contain	O
both	O
amplitude	O
and	O
phase	O
information	O
.	O
</s>
<s>
The	O
monopulse	B-Algorithm
method	O
does	O
not	O
require	O
that	O
the	O
measured	O
signals	O
are	O
pulsed	O
.	O
</s>
<s>
Conical	B-Algorithm
scanning	I-Algorithm
is	O
not	O
considered	O
to	O
be	O
a	O
form	O
of	O
monopulse	B-Algorithm
radar	I-Algorithm
,	O
but	O
the	O
following	O
summary	O
provides	O
background	O
that	O
can	O
aid	O
understanding	O
.	O
</s>
<s>
One	O
problem	O
with	O
this	O
approach	O
is	O
that	O
radar	B-Application
signals	O
often	O
change	O
in	O
amplitude	O
for	O
reasons	O
that	O
have	O
nothing	O
to	O
do	O
with	O
beam	O
position	O
.	O
</s>
<s>
Since	O
conical	B-Algorithm
scanning	I-Algorithm
systems	O
depend	O
on	O
the	O
signal	O
growing	O
or	O
weakening	O
due	O
only	O
to	O
the	O
position	O
of	O
the	O
target	O
relative	O
to	O
the	O
beam	O
,	O
such	O
changes	O
in	O
reflected	O
signal	O
can	O
cause	O
it	O
to	O
be	O
"	O
confused	O
"	O
about	O
the	O
position	O
of	O
the	O
target	O
within	O
the	O
beam	O
's	O
scanning	O
area	O
.	O
</s>
<s>
The	O
jammer	O
simply	O
has	O
to	O
send	O
out	O
signals	O
on	O
the	O
radar	B-Application
's	O
frequency	O
with	O
enough	O
strength	O
to	O
make	O
it	O
think	O
that	O
was	O
the	O
strongest	O
return	O
.	O
</s>
<s>
The	O
British	O
used	O
them	O
during	O
World	O
War	O
II	O
against	O
the	O
German	O
conical-scanning	O
Würzburg	O
radar	B-Application
.	O
</s>
<s>
Monopulse	B-Algorithm
radars	I-Algorithm
are	O
similar	O
in	O
general	O
construction	O
to	O
conical	B-Algorithm
scanning	I-Algorithm
systems	O
,	O
but	O
split	O
the	O
beam	O
into	O
parts	O
and	O
then	O
send	O
the	O
two	O
resulting	O
signals	O
out	O
of	O
the	O
antenna	O
in	O
slightly	O
different	O
directions	O
.	O
</s>
<s>
If	O
the	O
lobes	O
are	O
closely	O
spaced	O
,	O
this	O
signal	O
can	O
produce	O
a	O
high	O
degree	O
of	O
pointing	O
accuracy	O
within	O
the	O
beam	O
,	O
adding	O
to	O
the	O
natural	O
accuracy	O
of	O
the	O
conical	B-Algorithm
scanning	I-Algorithm
system	O
.	O
</s>
<s>
Whereas	O
classical	O
conical	O
scan	O
systems	O
generate	O
pointing	O
accuracy	O
on	O
the	O
order	O
of	O
0.1	O
degree	O
,	O
monopulse	B-Algorithm
radars	I-Algorithm
generally	O
improve	O
this	O
by	O
a	O
factor	O
of	O
10	O
,	O
and	O
advanced	O
tracking	O
radars	B-Application
like	O
the	O
AN/FPS	O
-16	O
are	O
accurate	O
to	O
0.006	O
degrees	O
.	O
</s>
<s>
Jamming	O
resistance	O
is	O
greatly	O
improved	O
over	O
conical	B-Algorithm
scanning	I-Algorithm
.	O
</s>
<s>
Against	O
monopulse	B-Algorithm
systems	O
,	O
ECM	O
has	O
generally	O
resorted	O
to	O
broadcasting	O
white	O
noise	O
to	O
simply	O
blind	O
the	O
radar	B-Application
,	O
instead	O
of	O
attempting	O
to	O
produce	O
false	O
localized	O
returns	O
.	O
</s>
<s>
Monopulse	B-Algorithm
antennas	O
produce	O
a	O
sum	O
signal	O
and	O
two	O
delta	O
signals	O
.	O
</s>
<s>
A	O
calibration	O
signal	O
is	O
injected	O
into	O
the	O
receive	O
path	O
when	O
the	O
radar	B-Application
is	O
idle	O
,	O
and	O
this	O
establishes	O
a	O
known	O
phase	O
shift	O
between	O
different	O
microwave	O
signal	O
paths	O
(	O
quiescent	O
mode	O
)	O
.	O
</s>
<s>
An	O
explanation	O
of	O
how	O
real	O
and	O
imaginary	O
parts	O
are	O
used	O
with	O
RADAR	B-Application
can	O
be	O
found	O
in	O
the	O
description	O
of	O
pulse	B-Algorithm
Doppler	I-Algorithm
.	O
</s>
<s>
On	O
mechanically	O
steered	O
radar	B-Application
,	O
the	O
vertical	O
angle	O
error	O
drives	O
a	O
motor	O
that	O
moves	O
the	O
antenna	O
up	O
or	O
down	O
,	O
and	O
the	O
horizontal	O
angle	O
error	O
drives	O
a	O
motor	O
that	O
steers	O
the	O
antenna	O
left	O
or	O
right	O
.	O
</s>
<s>
The	O
four-quadrant	O
array	B-Algorithm
antenna	I-Algorithm
consists	O
of	O
four	O
sub-arrays	O
.	O
</s>
<s>
The	O
sub-arrays	O
are	O
separated	O
by	O
a	O
distance	O
d	O
.	O
The	O
angle	O
θ	O
(	O
in	O
either	O
elevation	O
or	O
azimuth	O
)	O
is	O
estimated	O
from	O
the	O
monopulse	B-Algorithm
ratio	O
,	O
which	O
is	O
the	O
ratio	O
of	O
the	O
difference	O
signal	O
over	O
the	O
sum	O
signal	O
.	O
</s>
<s>
Antenna	O
error	O
signals	O
are	O
used	O
to	O
create	O
feedback	O
as	O
part	O
of	O
a	O
RADAR	B-Application
system	I-Application
that	O
can	O
track	O
aircraft	O
.	O
</s>
<s>
For	O
a	O
track	B-Algorithm
while	I-Algorithm
scan	I-Algorithm
radar	B-Application
,	O
position	O
and	O
velocity	O
is	O
maintained	O
for	O
multiple	O
aircraft	O
.	O
</s>
<s>
The	O
monopulse	B-Algorithm
angle	O
error	O
information	O
that	O
is	O
received	O
is	O
used	O
to	O
adjust	O
the	O
position	O
and	O
velocity	O
data	O
for	O
the	O
aircraft	O
.	O
</s>
<s>
This	O
is	O
a	O
common	O
mode	O
with	O
phased	O
array	O
radar	B-Application
systems	I-Application
.	O
</s>
<s>
Amplitude-Comparison	B-Algorithm
Monopulse	I-Algorithm
provides	O
an	O
explanation	O
of	O
the	O
antenna	O
signals	O
involved	O
in	O
this	O
process	O
.	O
</s>
<s>
Pulse	B-Algorithm
Doppler	I-Algorithm
RADAR	I-Algorithm
signal	O
processing	O
uses	O
this	O
technique	O
.	O
</s>
<s>
This	O
is	O
combined	O
with	O
conical	B-Algorithm
scanning	I-Algorithm
or	O
monopulse	B-Algorithm
to	O
improve	O
track	O
reliability	O
.	O
</s>
<s>
Conical	O
scan	O
and	O
monopulse	B-Algorithm
antennas	O
are	O
susceptible	O
to	O
interference	O
from	O
weather	O
phenomenon	O
and	O
stationary	O
objects	O
.	O
</s>
<s>
Systems	O
with	O
no	O
Pulse	B-Algorithm
Doppler	I-Algorithm
tracking	O
mode	O
may	O
remain	O
aimed	O
at	O
irrelevant	O
objects	O
like	O
trees	O
or	O
clouds	O
.	O
</s>
<s>
Monopulse	B-Algorithm
radar	I-Algorithm
was	O
extremely	O
"	O
high	O
tech	O
"	O
when	O
it	O
was	O
first	O
introduced	O
by	O
Robert	O
M	O
.	O
Page	O
in	O
1943	O
in	O
a	O
Naval	O
Research	O
Laboratory	O
experiment	O
.	O
</s>
<s>
Early	O
uses	O
included	O
the	O
Nike	O
Ajax	O
missile	O
,	O
which	O
demanded	O
very	O
high	O
accuracy	O
,	O
or	O
for	O
tracking	O
radars	B-Application
used	O
for	O
measuring	O
various	O
rocket	B-Application
launches	O
.	O
</s>
<s>
The	O
world	O
's	O
first	O
airborne	O
monopulse	B-Algorithm
radar	I-Algorithm
system	O
was	O
the	O
British	O
Ferranti-designed	O
AIRPASS	O
system	O
which	O
went	O
into	O
service	O
in	O
1960	O
on	O
the	O
RAF	O
's	O
English	O
Electric	O
Lightning	O
interceptor	O
aircraft	O
.	O
</s>
<s>
An	O
early	O
monopulse	B-Algorithm
radar	I-Algorithm
development	O
,	O
in	O
1958	O
,	O
was	O
the	O
AN/FPS	O
-16	O
,	O
on	O
which	O
NRL	O
and	O
RCA	O
collaborated	O
.	O
</s>
<s>
These	O
radars	B-Application
played	O
an	O
important	O
part	O
in	O
the	O
Mercury	O
,	O
Gemini	O
,	O
and	O
early	O
Apollo	O
missions	O
,	O
being	O
deployed	O
in	O
Bermuda	O
,	O
Tannarive	O
,	O
and	O
Australia	O
,	O
among	O
other	O
places	O
for	O
that	O
purpose	O
.	O
</s>
<s>
One	O
of	O
the	O
larger	O
installations	O
first	O
appeared	O
in	O
the	O
1970s	O
as	O
the	O
US	O
Navy	O
's	O
AN/SPY	O
-1	O
radar	B-Application
used	O
on	O
the	O
Aegis	B-Application
Combat	I-Application
System	I-Application
,	O
and	O
MK-74	O
radar	B-Application
used	O
on	O
Tartar	O
Guided	O
Missile	O
Fire	O
Control	O
System	O
and	O
research	O
.	O
</s>
<s>
The	O
cost	O
and	O
complexity	O
of	O
implementing	O
monopulse	B-Algorithm
tracking	O
was	O
reduced	O
and	O
reliability	O
increased	O
when	O
digital	O
signal	O
processing	O
became	O
available	O
after	O
the	O
1970s	O
.	O
</s>
<s>
The	O
technology	O
is	O
found	O
in	O
most	O
modern	O
tracking	O
radars	B-Application
and	O
many	O
types	O
of	O
disposable	O
ordnance	O
like	O
missiles	O
.	O
</s>
