<s>
Inverse	B-Algorithm
synthetic-aperture	I-Algorithm
radar	I-Algorithm
(	O
ISAR	O
)	O
is	O
a	O
radar	O
technique	O
using	O
radar	B-Algorithm
imaging	I-Algorithm
to	O
generate	O
a	O
two-dimensional	O
high	O
resolution	O
image	O
of	O
a	O
target	O
.	O
</s>
<s>
It	O
is	O
analogous	O
to	O
conventional	O
SAR	B-Application
,	O
except	O
that	O
ISAR	O
technology	O
uses	O
the	O
movement	O
of	O
the	O
target	O
rather	O
than	O
the	O
emitter	O
to	O
create	O
the	O
synthetic	O
aperture	O
.	O
</s>
<s>
ISAR	O
radars	O
have	O
a	O
significant	O
role	O
aboard	O
maritime	O
patrol	O
aircraft	O
to	O
provide	O
them	O
with	O
radar	B-Algorithm
image	I-Algorithm
of	O
sufficient	O
quality	O
to	O
allow	O
it	O
to	O
be	O
used	O
for	O
target	B-Algorithm
recognition	I-Algorithm
purposes	O
.	O
</s>
<s>
The	O
rotation	O
will	O
result	O
in	O
the	O
generation	O
of	O
cross	O
range	O
dependent	O
Doppler	O
frequencies	O
which	O
can	O
be	O
sorted	O
spatially	O
by	O
a	O
Fourier	B-Algorithm
transform	I-Algorithm
.	O
</s>
<s>
For	O
small	O
angles	O
,	O
an	O
ISAR	O
image	O
is	O
the	O
2-dimensional	O
Fourier	B-Algorithm
transform	I-Algorithm
of	O
the	O
received	O
signal	O
as	O
a	O
function	O
of	O
frequency	O
and	O
target	O
aspect	O
angle	O
.	O
</s>
<s>
This	O
Doppler	O
history	O
can	O
not	O
be	O
processed	O
directly	O
by	O
a	O
Fourier	B-Algorithm
transform	I-Algorithm
because	O
of	O
the	O
smeared	O
Doppler	O
frequency	O
history	O
resulting	O
in	O
the	O
loss	O
of	O
cross	O
range	O
resolution	O
.	O
</s>
<s>
The	O
maximum	O
rotation	O
angle	O
which	O
can	O
be	O
processed	O
by	O
an	O
unmodified	O
Fourier	B-Algorithm
transform	I-Algorithm
is	O
determined	O
by	O
the	O
constraint	O
that	O
the	O
aperture	O
phase	O
error	O
across	O
the	O
synthesized	O
aperture	O
should	O
vary	O
by	O
less	O
than	O
a	O
specified	O
(	O
arbitrary	O
)	O
amount	O
,	O
for	O
example	O
45	O
degrees	O
.	O
</s>
<s>
The	O
sidelobes	O
are	O
due	O
to	O
data	O
truncation	B-Algorithm
and	O
can	O
be	O
reduced	O
by	O
the	O
application	O
of	O
appropriate	O
window	O
functions	O
.	O
</s>
