<s>
Continuous-wave	B-Algorithm
radar	I-Algorithm
(	O
CW	B-Algorithm
radar	I-Algorithm
)	O
is	O
a	O
type	O
of	O
radar	B-Application
system	I-Application
where	O
a	O
known	O
stable	O
frequency	O
continuous	O
wave	O
radio	O
energy	O
is	O
transmitted	O
and	O
then	O
received	O
from	O
any	O
reflecting	O
objects	O
.	O
</s>
<s>
Individual	O
objects	O
can	O
be	O
detected	O
using	O
the	O
Doppler	B-Algorithm
effect	I-Algorithm
,	O
which	O
causes	O
the	O
received	O
signal	O
to	O
have	O
a	O
different	O
frequency	O
from	O
the	O
transmitted	O
signal	O
,	O
allowing	O
it	O
to	O
be	O
detected	O
by	O
filtering	O
out	O
the	O
transmitted	O
frequency	O
.	O
</s>
<s>
Doppler-analysis	O
of	O
radar	B-Application
returns	O
can	O
allow	O
the	O
filtering	O
out	O
of	O
slow	O
or	O
non-moving	O
objects	O
,	O
thus	O
offering	O
immunity	O
to	O
interference	O
from	O
large	O
stationary	O
objects	O
and	O
slow-moving	O
clutter	O
.	O
</s>
<s>
CW	B-Algorithm
radar	I-Algorithm
systems	O
are	O
used	O
at	O
both	O
ends	O
of	O
the	O
range	O
spectrum	O
.	O
</s>
<s>
The	O
main	O
advantage	O
of	O
CW	B-Algorithm
radar	I-Algorithm
is	O
that	O
energy	O
is	O
not	O
pulsed	B-Algorithm
so	O
these	O
are	O
much	O
simpler	O
to	O
manufacture	O
and	O
operate	O
.	O
</s>
<s>
Continuous-wave	B-Algorithm
radar	I-Algorithm
maximize	O
total	O
power	O
on	O
a	O
target	O
because	O
the	O
transmitter	O
is	O
broadcasting	O
continuously	O
.	O
</s>
<s>
The	O
military	O
uses	O
continuous-wave	B-Algorithm
radar	I-Algorithm
to	O
guide	O
semi-active	O
radar	B-Application
homing	O
(	O
SARH	O
)	O
air-to-air	O
missiles	O
,	O
such	O
as	O
the	O
U.S.	O
AIM-7	O
Sparrow	O
and	O
the	O
Standard	O
missile	O
family	O
.	O
</s>
<s>
The	O
launch	O
aircraft	O
illuminates	O
the	O
target	O
with	O
a	O
CW	B-Algorithm
radar	I-Algorithm
signal	O
,	O
and	O
the	O
missile	O
homes	O
in	O
on	O
the	O
reflected	O
radio	O
waves	O
.	O
</s>
<s>
Most	O
modern	O
air	O
combat	O
radars	B-Application
,	O
even	O
pulse	B-Algorithm
Doppler	I-Algorithm
sets	O
,	O
have	O
a	O
CW	O
function	O
for	O
missile	O
guidance	O
purposes	O
.	O
</s>
<s>
Maximum	O
distance	O
in	O
a	O
continuous-wave	B-Algorithm
radar	I-Algorithm
is	O
determined	O
by	O
the	O
overall	O
bandwidth	O
and	O
transmitter	O
power	O
.	O
</s>
<s>
Frequency	O
domain	O
receivers	O
used	O
for	O
continuous-wave	O
Doppler	B-Algorithm
radar	I-Algorithm
receivers	O
are	O
very	O
different	O
from	O
conventional	O
radar	B-Application
receivers	O
.	O
</s>
<s>
A	O
CW	B-Algorithm
radar	I-Algorithm
is	O
said	O
to	O
be	O
matched	O
when	O
the	O
receiver	O
filter	O
size	O
matches	O
the	O
RMS	O
bandwidth	O
of	O
the	O
FM	O
noise	O
on	O
the	O
transmit	O
signal	O
.	O
</s>
<s>
There	O
are	O
two	O
types	O
of	O
continuous-wave	B-Algorithm
radar	I-Algorithm
:	O
unmodulated	O
continuous-wave	O
and	O
modulated	O
continuous-wave	O
.	O
</s>
<s>
This	O
kind	O
of	O
radar	B-Application
can	O
cost	O
less	O
than	O
$10	O
(	O
2021	O
)	O
.	O
</s>
<s>
Return	O
frequencies	O
are	O
shifted	O
away	O
from	O
the	O
transmitted	O
frequency	O
based	O
on	O
the	O
Doppler	B-Algorithm
effect	I-Algorithm
when	O
objects	O
are	O
moving	O
.	O
</s>
<s>
This	O
type	O
of	O
radar	B-Application
is	O
typically	O
used	O
with	O
competition	O
sports	O
,	O
like	O
golf	O
,	O
tennis	O
,	O
baseball	O
,	O
NASCAR	O
racing	O
,	O
and	O
some	O
smart-home	O
appliances	O
including	O
light-bulbs	O
and	O
motion	O
sensors	O
.	O
</s>
<s>
Since	O
the	O
usual	O
variation	O
of	O
targets	O
 '	O
speed	O
of	O
a	O
radar	B-Application
is	O
much	O
smaller	O
than	O
,	O
it	O
is	O
possible	O
to	O
simplify	O
with	O
:	O
</s>
<s>
Continuous-wave	B-Algorithm
radar	I-Algorithm
without	O
frequency	O
modulation	O
(	O
FM	O
)	O
only	O
detects	O
moving	O
targets	O
,	O
as	O
stationary	O
targets	O
(	O
along	O
the	O
line	O
of	O
sight	O
)	O
will	O
not	O
cause	O
a	O
Doppler	O
shift	O
.	O
</s>
<s>
–	O
is	O
a	O
short-range	O
measuring	O
radar	B-Application
set	O
capable	O
of	O
determining	O
distance	O
.	O
</s>
<s>
This	O
increases	O
reliability	O
by	O
providing	O
distance	O
measurement	O
along	O
with	O
speed	O
measurement	O
,	O
which	O
is	O
essential	O
when	O
there	O
is	O
more	O
than	O
one	O
source	O
of	O
reflection	O
arriving	O
at	O
the	O
radar	B-Application
antenna	O
.	O
</s>
<s>
This	O
kind	O
of	O
radar	B-Application
is	O
often	O
used	O
as	O
"	O
radar	B-Application
altimeter	O
"	O
to	O
measure	O
the	O
exact	O
height	O
during	O
the	O
landing	O
procedure	O
of	O
aircraft	O
.	O
</s>
<s>
It	O
is	O
also	O
used	O
as	O
early-warning	B-Algorithm
radar	I-Algorithm
,	O
wave	B-Algorithm
radar	I-Algorithm
,	O
and	O
proximity	O
sensors	O
.	O
</s>
<s>
While	O
early	O
implementations	O
,	O
such	O
as	O
the	O
APN-1	O
Radar	B-Application
Altimeter	O
of	O
the	O
1940s	O
,	O
were	O
designed	O
for	O
short	O
ranges	O
,	O
Over	O
The	O
Horizon	O
Radars	B-Application
(	O
OTHR	O
)	O
such	O
as	O
the	O
Jindalee	O
Operational	O
Radar	B-Application
Network	O
(	O
JORN	O
)	O
are	O
designed	O
to	O
survey	O
intercontinental	O
distances	O
of	O
some	O
thousands	O
of	O
kilometres	O
.	O
</s>
<s>
Echoes	O
from	O
a	O
target	O
are	O
then	O
mixed	O
with	O
the	O
transmitted	O
signal	O
to	O
produce	O
a	O
beat	B-Application
signal	I-Application
which	O
will	O
give	O
the	O
distance	O
of	O
the	O
target	O
after	O
demodulation	O
.	O
</s>
<s>
The	O
radar	B-Application
will	O
report	O
incorrect	O
distance	O
for	O
reflections	O
from	O
distances	O
beyond	O
the	O
instrumented	O
range	O
,	O
such	O
as	O
from	O
the	O
moon	O
.	O
</s>
<s>
This	O
allows	O
range	O
and	O
velocity	O
to	O
be	O
found	O
with	O
one	O
radar	B-Application
set	O
.	O
</s>
<s>
The	O
transmitted	O
frequency	O
is	O
used	O
to	O
down-convert	O
the	O
receive	O
signal	O
to	O
baseband	B-Algorithm
,	O
and	O
the	O
amount	O
of	O
frequency	O
shift	O
between	O
the	O
transmit	O
signal	O
and	O
the	O
reflected	O
signal	O
increases	O
with	O
time	O
delay	O
(	O
distance	O
)	O
.	O
</s>
<s>
With	O
the	O
advent	O
of	O
modern	O
electronics	O
,	O
digital	B-General_Concept
signal	I-General_Concept
processing	I-General_Concept
is	O
used	O
for	O
most	O
detection	O
processing	O
.	O
</s>
<s>
where	O
is	O
the	O
radar	B-Application
frequency	O
sweep	O
amount	O
and	O
is	O
the	O
time	O
to	O
complete	O
the	O
frequency	O
sweep	O
.	O
</s>
<s>
,	O
where	O
is	O
the	O
round	O
trip	O
time	O
of	O
the	O
radar	B-Application
energy	O
.	O
</s>
<s>
A	O
time	O
delay	O
is	O
introduced	O
in	O
transit	O
between	O
the	O
radar	B-Application
and	O
the	O
reflector	O
.	O
</s>
<s>
Receiver	O
demodulation	O
is	O
used	O
with	O
FMCW	O
similar	O
to	O
the	O
receiver	O
demodulation	O
strategy	O
used	O
with	O
pulse	B-Algorithm
compression	I-Algorithm
.	O
</s>
<s>
Practical	O
systems	O
introduce	O
reverse	O
FM	O
on	O
the	O
receive	O
signal	O
using	O
digital	B-General_Concept
signal	I-General_Concept
processing	I-General_Concept
before	O
the	O
fast	O
Fourier	O
transform	O
process	O
is	O
used	O
to	O
produce	O
the	O
spectrum	O
.	O
</s>
<s>
There	O
are	O
two	O
different	O
antenna	O
configurations	O
used	O
with	O
continuous-wave	B-Algorithm
radar	I-Algorithm
:	O
monostatic	B-Algorithm
radar	I-Algorithm
,	O
and	O
bistatic	B-Algorithm
radar	I-Algorithm
.	O
</s>
<s>
The	O
radar	B-Application
receive	O
antenna	O
is	O
located	O
nearby	O
the	O
radar	B-Application
transmit	O
antenna	O
in	O
monostatic	B-Algorithm
radar	I-Algorithm
.	O
</s>
<s>
Feed-through	B-Algorithm
null	I-Algorithm
is	O
typically	O
required	O
to	O
eliminate	O
bleed-through	O
between	O
the	O
transmitter	O
and	O
receiver	O
to	O
increase	O
sensitivity	O
in	O
practical	O
systems	O
.	O
</s>
<s>
This	O
is	O
typically	O
used	O
with	O
continuous-wave	O
angle	O
tracking	O
(	O
CWAT	O
)	O
radar	B-Application
receivers	O
that	O
are	O
interoperable	O
with	O
surface-to-air	O
missile	O
systems	O
.	O
</s>
<s>
This	O
technique	O
is	O
used	O
with	O
the	O
least	O
expensive	O
kinds	O
of	O
radar	B-Application
,	O
such	O
as	O
those	O
used	O
for	O
traffic	O
monitoring	O
and	O
sports	O
.	O
</s>
<s>
The	O
radar	B-Application
receive	O
antenna	O
is	O
located	O
far	O
from	O
the	O
radar	B-Application
transmit	O
antenna	O
in	O
bistatic	B-Algorithm
radar	I-Algorithm
.	O
</s>
<s>
This	O
is	O
typically	O
used	O
with	O
semi-active	O
radar	B-Application
homing	O
including	O
most	O
surface-to-air	O
missile	O
systems	O
.	O
</s>
<s>
The	O
transmit	O
radar	B-Application
is	O
typically	O
located	O
near	O
the	O
missile	O
launcher	O
.	O
</s>
<s>
The	O
receive	O
antenna	O
that	O
is	O
aimed	O
at	O
the	O
transmit	O
antenna	O
is	O
used	O
to	O
develop	O
the	O
feed-through	B-Algorithm
null	I-Algorithm
,	O
which	O
allows	O
the	O
target	O
receiver	O
to	O
operate	O
reliably	O
in	O
or	O
near	O
the	O
main	O
beam	O
of	O
the	O
antenna	O
.	O
</s>
<s>
This	O
technique	O
is	O
used	O
in	O
semi-active	O
radar	B-Application
homing	O
.	O
</s>
<s>
Null	O
and	O
filter	O
approaches	O
must	O
be	O
used	O
with	O
bistatic	B-Algorithm
radar	I-Algorithm
,	O
like	O
semi-active	O
radar	B-Application
homing	O
,	O
for	O
practical	O
reasons	O
because	O
side-lobes	O
from	O
the	O
illumination	O
radar	B-Application
will	O
illuminate	O
the	O
environment	O
in	O
addition	O
to	O
the	O
main-lobe	O
illumination	O
on	O
the	O
target	O
.	O
</s>
<s>
Similar	O
constraints	O
apply	O
to	O
ground-based	O
CW	B-Algorithm
radar	I-Algorithm
.	O
</s>
<s>
Interruption	O
applies	O
to	O
cheap	O
hand	O
held	O
mono-static	O
radar	B-Application
systems	O
(	O
police	O
radar	B-Application
and	O
sporting	O
goods	O
)	O
.	O
</s>
<s>
While	O
interrupted	O
carrier	O
systems	O
are	O
not	O
considered	O
to	O
be	O
CW	O
systems	O
,	O
performance	O
characteristics	O
are	O
sufficiently	O
similar	O
to	O
group	O
interrupted	O
CW	O
systems	O
with	O
pure	O
CW	B-Algorithm
radar	I-Algorithm
because	O
the	O
pulse	O
rate	O
is	O
high	O
enough	O
that	O
range	O
measurements	O
cannot	O
be	O
done	O
without	O
frequency	O
modulation	O
(	O
FM	O
)	O
.	O
</s>
<s>
The	O
interruption	O
concept	O
is	O
widely	O
used	O
,	O
especially	O
in	O
long-range	O
radar	B-Application
applications	O
where	O
the	O
receiver	O
sensitivity	O
is	O
very	O
important	O
.	O
</s>
<s>
Because	O
of	O
simplicity	O
,	O
CW	B-Algorithm
radar	I-Algorithm
are	O
inexpensive	O
to	O
manufacture	O
,	O
relatively	O
free	O
from	O
failure	O
,	O
cheap	O
to	O
maintain	O
,	O
and	O
fully	O
automated	O
.	O
</s>
<s>
More	O
sophisticated	O
CW	B-Algorithm
radar	I-Algorithm
systems	O
can	O
reliably	O
achieve	O
accurate	O
detections	O
exceeding	O
100km	O
distance	O
while	O
providing	O
missile	O
illumination	O
.	O
</s>
<s>
The	O
FMCW	O
ramp	O
can	O
be	O
compressed	O
providing	O
extra	O
signal	O
to	O
noise	O
gains	O
such	O
one	O
does	O
not	O
need	O
the	O
extra	O
power	O
that	O
pulse	O
radar	B-Application
using	O
a	O
no	O
FM	O
modulation	O
would	O
.	O
</s>
<s>
That	O
technique	O
can	O
be	O
used	O
to	O
produce	O
inexpensive	O
stealthy	O
low-power	O
radar	B-Application
.	O
</s>
<s>
CW	O
performance	O
is	O
similar	O
to	O
Pulse-Doppler	B-Algorithm
radar	I-Algorithm
performance	O
for	O
this	O
reason	O
.	O
</s>
<s>
Unmodulated	O
continuous	B-Algorithm
wave	I-Algorithm
radar	I-Algorithm
cannot	O
measure	O
distance	O
.	O
</s>
<s>
Reflections	O
from	O
small	O
objects	O
directly	O
in	O
front	O
of	O
the	O
receiver	O
can	O
be	O
overwhelmed	O
by	O
reflections	O
entering	O
antenna	O
side-lobes	O
from	O
large	O
object	O
located	O
to	O
the	O
side	O
,	O
above	O
,	O
or	O
behind	O
the	O
radar	B-Application
,	O
such	O
as	O
trees	O
with	O
wind	O
blowing	O
through	O
the	O
leaves	O
,	O
tall	O
grass	O
,	O
sea	O
surface	O
,	O
freight	O
trains	O
,	O
busses	O
,	O
trucks	O
,	O
and	O
aircraft	O
.	O
</s>
<s>
Small	O
radar	B-Application
systems	I-Application
that	O
lack	O
range	O
modulation	O
are	O
only	O
reliable	O
when	O
used	O
with	O
one	O
object	O
in	O
a	O
sterile	O
environment	O
free	O
from	O
vegetation	O
,	O
aircraft	O
,	O
birds	O
,	O
weather	O
phenomenon	O
,	O
and	O
other	O
nearby	O
vehicles	O
.	O
</s>
<s>
This	O
is	O
a	O
typical	O
problem	O
with	O
radar	B-Application
speed	O
guns	O
used	O
by	O
law	O
enforcement	O
officers	O
,	O
NASCAR	O
events	O
,	O
and	O
sports	O
,	O
like	O
baseball	O
,	O
golf	O
,	O
and	O
tennis	O
.	O
</s>
<s>
Interference	O
from	O
a	O
second	O
radar	B-Application
,	O
automobile	O
ignition	O
,	O
other	O
moving	O
objects	O
,	O
moving	O
fan	O
blades	O
on	O
the	O
intended	O
target	O
,	O
and	O
other	O
radio	O
frequency	O
sources	O
will	O
corrupt	O
measurements	O
.	O
</s>
<s>
These	O
systems	O
are	O
limited	O
by	O
wavelength	O
,	O
which	O
is	O
0.02	O
meter	O
at	O
Ku	B-Algorithm
band	I-Algorithm
,	O
so	O
the	O
beam	O
spread	O
exceeds	O
45	O
degrees	O
if	O
the	O
antenna	O
is	O
smaller	O
than	O
12inches	O
(	O
0.3	O
meter	O
)	O
.	O
</s>
<s>
Significant	O
antenna	O
side-lobes	O
extend	O
in	O
all	O
directions	O
unless	O
the	O
antenna	O
is	O
larger	O
than	O
the	O
vehicle	O
on	O
which	O
the	O
radar	B-Application
is	O
mounted	O
.	O
</s>
