<s>
Low-frequency	B-Algorithm
radar	I-Algorithm
is	O
radar	B-Application
which	O
uses	O
frequencies	O
lower	O
than	O
1GHz	O
such	O
as	O
L-band	O
,	O
UHF	O
,	O
VHF	O
,	O
and	O
HF	O
,	O
as	O
opposed	O
to	O
the	O
usual	O
radar	B-Application
bands	O
,	O
which	O
range	O
from	O
2GHz	O
to	O
40GHz.The	O
radar	B-Application
cross	O
section	O
of	O
any	O
target	O
depends	O
on	O
the	O
frequency	O
transmitted	O
by	O
the	O
radar	B-Application
.	O
</s>
<s>
Below	O
900MHz	O
the	O
target	O
radar	B-Application
cross	O
section	O
increases	O
exponentially	O
,	O
however	O
the	O
increased	O
radar	B-Application
cross	O
section	O
means	O
that	O
there	O
is	O
also	O
much	O
more	O
radar	B-Application
return	O
from	O
undesirable	O
sources	O
,	O
such	O
as	O
cloud	O
cover	O
and	O
rain	O
(	O
cf	O
.	O
</s>
<s>
weather	B-Application
radar	I-Application
)	O
.	O
</s>
<s>
It	O
is	O
because	O
of	O
this	O
that	O
radars	B-Application
traditionally	O
use	O
much	O
higher	O
frequencies	O
,	O
with	O
an	O
exception	O
being	O
the	O
radars	B-Application
operated	O
in	O
the	O
3-30MHz	O
band	O
which	O
are	O
used	O
as	O
over-the-horizon	B-Architecture
radar	I-Architecture
stations	O
because	O
signals	O
in	O
that	O
range	O
are	O
able	O
to	O
reflect	O
off	O
the	O
ionosphere	O
.	O
</s>
<s>
Recent	O
interest	O
has	O
accumulated	O
in	O
developing	O
radars	B-Application
which	O
operate	O
in	O
these	O
low	O
frequencies	O
to	O
help	O
counter	O
the	O
advancement	O
in	O
stealth	O
technology	O
by	O
applying	O
advanced	O
digital	B-General_Concept
signal	I-General_Concept
processing	I-General_Concept
to	O
these	O
bands	O
in	O
order	O
to	O
reduce	O
radar	B-Application
clutter	O
.	O
</s>
<s>
If	O
the	O
radar	B-Application
wavelength	O
is	O
roughly	O
twice	O
the	O
size	O
of	O
the	O
target	O
,	O
a	O
half-wave	O
resonance	O
effect	O
can	O
still	O
generate	O
a	O
significant	O
return	O
.	O
</s>
<s>
However	O
,	O
low-frequency	B-Algorithm
radar	I-Algorithm
is	O
limited	O
by	O
shortage	O
of	O
unused	O
frequencies	O
,	O
lack	O
of	O
accuracy	O
given	O
the	O
long	O
wavelength	O
,	O
and	O
by	O
the	O
radar	B-Application
's	O
size	O
,	O
making	O
it	O
difficult	O
to	O
transport	O
and	O
making	O
for	O
an	O
easy	O
target	O
.	O
</s>
