<s>
Conical	B-Algorithm
scanning	I-Algorithm
is	O
a	O
system	O
used	O
in	O
early	O
radar	B-Application
units	O
to	O
improve	O
their	O
accuracy	O
,	O
as	O
well	O
as	O
making	O
it	O
easier	O
to	O
steer	O
the	O
antenna	O
properly	O
to	O
point	O
at	O
a	O
target	O
.	O
</s>
<s>
Conical	B-Algorithm
scanning	I-Algorithm
is	O
similar	O
in	O
concept	O
to	O
the	O
earlier	O
lobe	B-Algorithm
switching	I-Algorithm
concept	O
used	O
on	O
some	O
of	O
the	O
earliest	O
radars	B-Application
,	O
and	O
many	O
examples	O
of	O
lobe	B-Algorithm
switching	I-Algorithm
sets	O
were	O
modified	O
in	O
the	O
field	O
to	O
conical	B-Algorithm
scanning	I-Algorithm
during	O
World	O
War	O
II	O
,	O
notably	O
the	O
German	O
Würzburg	O
radar	B-Application
.	O
</s>
<s>
Potential	O
failure	O
modes	O
and	O
susceptibility	O
to	O
deception	O
jamming	O
led	O
to	O
the	O
replacement	O
of	O
conical	O
scan	O
systems	O
with	O
monopulse	B-Algorithm
radar	I-Algorithm
sets	O
.	O
</s>
<s>
The	O
spin-stabilized	O
Pioneer	O
10	O
and	O
Pioneer	O
11	O
probes	O
used	O
onboard	O
conical	B-Algorithm
scanning	I-Algorithm
maneuvers	O
to	O
track	O
Earth	O
in	O
its	O
orbit	O
.	O
</s>
<s>
A	O
typical	O
radar	B-Application
antenna	O
commonly	O
has	O
a	O
beam	O
width	O
of	O
a	O
few	O
degrees	O
.	O
</s>
<s>
While	O
this	O
is	O
adequate	O
for	O
locating	O
the	O
target	O
in	O
an	O
early	B-Algorithm
warning	I-Algorithm
role	O
,	O
it	O
is	O
not	O
nearly	O
accurate	O
enough	O
for	O
gun	O
laying	O
,	O
which	O
demands	O
accuracies	O
on	O
the	O
order	O
of	O
0.1	O
degrees	O
.	O
</s>
<s>
In	O
order	O
to	O
have	O
the	O
radar	B-Application
system	I-Application
follow	O
a	O
moving	O
target	O
automatically	O
,	O
it	O
is	O
necessary	O
to	O
have	O
a	O
control	O
system	O
that	O
keeps	O
the	O
antenna	O
beam	O
pointing	O
at	O
the	O
target	O
as	O
it	O
moves	O
.	O
</s>
<s>
The	O
radar	B-Application
receiver	O
will	O
get	O
maximum	O
returned	O
signal	O
strength	O
when	O
the	O
target	O
is	O
in	O
the	O
beam	O
center	O
.	O
</s>
<s>
The	O
radar	B-Application
will	O
have	O
no	O
information	O
as	O
to	O
which	O
direction	O
the	O
target	O
has	O
moved	O
,	O
and	O
therefore	O
no	O
indication	O
as	O
to	O
which	O
direction	O
to	O
move	O
the	O
antenna	O
to	O
follow	O
it	O
.	O
</s>
<s>
Conical	B-Algorithm
scanning	I-Algorithm
addresses	O
this	O
problem	O
by	O
moving	O
the	O
radar	B-Application
beam	O
slightly	O
off	O
center	O
from	O
the	O
antenna	O
's	O
midline	O
,	O
or	O
boresight	O
,	O
and	O
then	O
rotating	O
it	O
.	O
</s>
<s>
Given	O
an	O
example	O
antenna	O
that	O
generates	O
a	O
beam	O
of	O
2	O
degrees	O
width	O
fairly	O
typical	O
a	O
conical	B-Algorithm
scanning	I-Algorithm
radar	B-Application
might	O
move	O
the	O
beam	O
1.5	O
degrees	O
to	O
one	O
side	O
of	O
the	O
centerline	O
by	O
offsetting	O
the	O
feed	O
slightly	O
.	O
</s>
<s>
Additionally	O
,	O
the	O
portion	O
covering	O
the	O
centerline	O
is	O
near	O
the	O
edge	O
of	O
the	O
radar	B-Application
lobe	O
,	O
where	O
sensitivity	O
is	O
falling	O
off	O
rapidly	O
.	O
</s>
<s>
An	O
aircraft	O
centered	O
in	O
the	O
beam	O
is	O
in	O
the	O
area	O
where	O
even	O
small	O
motions	O
will	O
result	O
in	O
a	O
noticeable	O
change	O
in	O
return	O
,	O
growing	O
much	O
stronger	O
along	O
the	O
direction	O
the	O
radar	B-Application
needs	O
to	O
move	O
.	O
</s>
<s>
Whilst	O
use	O
of	O
the	O
main	O
lobe	O
alone	O
might	O
allow	O
an	O
operator	O
to	O
"	O
hunt	O
"	O
for	O
the	O
strongest	O
return	O
and	O
thus	O
aim	O
the	O
antenna	O
within	O
a	O
degree	O
or	O
so	O
in	O
that	O
"	O
maximum	O
return	O
"	O
area	O
at	O
the	O
center	O
of	O
the	O
lobe	O
,	O
with	O
conical	B-Algorithm
scanning	I-Algorithm
much	O
smaller	O
movements	O
can	O
be	O
detected	O
,	O
and	O
accuracies	O
under	O
0.1	O
degree	O
are	O
possible	O
.	O
</s>
<s>
25	O
gun	O
fire	O
control	O
radar	B-Application
,	O
spiral	O
scan	O
mode	O
aided	O
target	O
acquisition	O
.	O
</s>
<s>
Since	O
the	O
lobe	O
is	O
being	O
rotated	O
around	O
the	O
midline	O
of	O
the	O
antenna	O
,	O
conical	B-Algorithm
scanning	I-Algorithm
is	O
only	O
really	O
appropriate	O
for	O
antennas	O
with	O
a	O
circular	O
cross	O
section	O
.	O
</s>
<s>
Most	O
other	O
forces	O
used	O
much	O
longer-wavelength	O
radars	B-Application
that	O
would	O
require	O
paraboloid	O
antennas	O
of	O
truly	O
enormous	O
size	O
,	O
and	O
instead	O
used	O
a	O
"	O
bedspring	O
"	O
arrangement	O
of	O
many	O
small	O
dipole	O
antennas	O
arranged	O
in	O
front	O
of	O
a	O
passive	O
reflector	O
.	O
</s>
<s>
To	O
arrange	O
conical	B-Algorithm
scanning	I-Algorithm
on	O
such	O
a	O
system	O
would	O
require	O
all	O
of	O
the	O
dipoles	O
to	O
be	O
moved	O
,	O
an	O
impractical	O
solution	O
.	O
</s>
<s>
For	O
this	O
reason	O
the	O
US	O
Army	O
simply	O
abandoned	O
their	O
early	O
gun	O
laying	O
radar	B-Application
,	O
the	O
SCR-268	O
.	O
</s>
<s>
This	O
was	O
not	O
particularly	O
annoying	O
,	O
given	O
that	O
they	O
were	O
in	O
the	O
process	O
of	O
introducing	O
their	O
own	O
microwave	B-Application
radar	I-Application
in	O
the	O
aftermath	O
of	O
the	O
Tizard	O
Mission	O
.	O
</s>
<s>
Automatic	O
guidance	O
for	O
the	O
antenna	O
,	O
and	O
thus	O
any	O
slaved	O
guns	O
or	O
weapons	O
,	O
can	O
be	O
added	O
to	O
a	O
conical	O
scan	O
radar	B-Application
without	O
too	O
much	O
trouble	O
.	O
</s>
<s>
In	O
these	O
cases	O
,	O
a	O
conical	O
scan	O
radar	B-Application
might	O
interpret	O
this	O
change	O
in	O
strength	O
as	O
a	O
change	O
in	O
position	O
.	O
</s>
<s>
This	O
problem	O
can	O
be	O
solved	O
by	O
using	O
two	O
simultaneous	O
overlapping	O
receiver	O
beams	O
leading	O
to	O
the	O
monopulse	B-Algorithm
radar	I-Algorithm
,	O
so-named	O
because	O
it	O
always	O
compares	O
signal	O
strength	O
from	O
a	O
single	O
pulse	O
against	O
itself	O
,	O
thereby	O
eliminating	O
problems	O
with	O
all	O
but	O
impossibly	O
fast	O
changes	O
in	O
signal	O
strength	O
.	O
</s>
<s>
Conical	O
scan	O
radars	B-Application
can	O
be	O
easily	O
jammed	O
.	O
</s>
<s>
If	O
the	O
target	O
knows	O
the	O
general	O
operating	O
parameters	O
of	O
the	O
radar	B-Application
,	O
it	O
is	O
possible	O
to	O
send	O
out	O
a	O
false	O
signal	O
timed	O
to	O
grow	O
and	O
fade	O
in	O
the	O
same	O
pattern	O
as	O
the	O
radar	B-Application
lobe	O
,	O
but	O
inverted	O
in	O
strength	O
.	O
</s>
<s>
That	O
is	O
,	O
the	O
false	O
signal	O
is	O
at	O
its	O
strongest	O
when	O
the	O
radar	B-Application
signal	O
is	O
the	O
weakest	O
(	O
the	O
lobe	O
is	O
on	O
the	O
"	O
far	O
side	O
"	O
of	O
the	O
antenna	O
compared	O
to	O
the	O
aircraft	O
)	O
,	O
and	O
weakest	O
when	O
the	O
signal	O
is	O
the	O
strongest	O
(	O
pointed	O
at	O
the	O
aircraft	O
)	O
.	O
</s>
<s>
When	O
added	O
together	O
with	O
the	O
"	O
real	O
"	O
signal	O
at	O
the	O
radar	B-Application
receiver	O
,	O
the	O
resulting	O
signal	O
is	O
"	O
always	O
strong	O
"	O
,	O
so	O
the	O
control	O
system	O
cannot	O
make	O
an	O
accurate	O
estimate	O
as	O
to	O
where	O
in	O
the	O
lobe	O
pattern	O
the	O
target	O
is	O
located	O
.	O
</s>
<s>
If	O
one	O
knows	O
that	O
the	O
signal	O
is	O
rotated	O
at	O
25	O
RPM	O
,	O
as	O
it	O
was	O
in	O
the	O
Würzburg	O
radar	B-Application
,	O
the	O
jammer	O
is	O
built	O
to	O
fade	O
from	O
maximum	O
to	O
zero	O
at	O
the	O
same	O
speed	O
,	O
25	O
times	O
a	O
minute	O
.	O
</s>
<s>
This	O
system	O
,	O
known	O
as	O
inverse	O
gain	O
jamming	O
,	O
was	O
used	O
operationally	O
by	O
the	O
Royal	O
Air	O
Force	O
against	O
the	O
Würzburg	O
radar	B-Application
during	O
World	O
War	O
II	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
arrange	O
a	O
radar	B-Application
so	O
the	O
lobes	O
are	O
not	O
being	O
moved	O
in	O
the	O
broadcaster	O
,	O
only	O
the	O
receiver	O
.	O
</s>
<s>
To	O
do	O
this	O
,	O
one	O
adds	O
a	O
second	O
antenna	O
with	O
the	O
rotating	O
lobe	O
for	O
reception	O
only	O
,	O
a	O
system	O
known	O
as	O
COSRO	O
,	O
for	O
Conical	O
Scan	O
on	O
Receive	O
Only	O
(	O
compare	O
to	O
LORO	O
,	O
a	O
similar	O
system	O
used	O
against	O
lobe	B-Algorithm
switching	I-Algorithm
radars	B-Application
)	O
.	O
</s>
