<s>
A	O
radar	B-Application
system	I-Application
uses	O
a	O
radio-frequency	O
electromagnetic	O
signal	O
reflected	O
from	O
a	O
target	O
to	O
determine	O
information	O
about	O
that	O
target	O
.	O
</s>
<s>
In	O
any	O
radar	B-Application
system	I-Application
,	O
the	O
signal	O
transmitted	O
and	O
received	O
will	O
exhibit	O
many	O
of	O
the	O
characteristics	O
described	O
below	O
.	O
</s>
<s>
The	O
carrier	O
is	O
an	O
RF	O
signal	O
,	O
typically	O
of	O
microwave	O
frequencies	O
,	O
which	O
is	O
usually	O
(	O
but	O
not	O
always	O
)	O
modulated	B-Application
to	O
allow	O
the	O
system	O
to	O
capture	O
the	O
required	O
data	O
.	O
</s>
<s>
In	O
simple	O
ranging	O
radars	B-Application
,	O
the	O
carrier	O
will	O
be	O
pulse	O
modulated	B-Application
and	O
in	O
continuous	O
wave	O
systems	O
,	O
such	O
as	O
Doppler	B-Algorithm
radar	I-Algorithm
,	O
modulation	B-Application
may	O
not	O
be	O
required	O
.	O
</s>
<s>
Most	O
systems	O
use	O
pulse	O
modulation	B-Application
,	O
with	O
or	O
without	O
other	O
supplementary	O
modulating	B-Application
signals	I-Application
.	O
</s>
<s>
Note	O
that	O
with	O
pulse	O
modulation	B-Application
,	O
the	O
carrier	O
is	O
simply	O
switched	O
on	O
and	O
off	O
in	O
sync	O
with	O
the	O
pulses	O
;	O
the	O
modulating	O
waveform	O
does	O
not	O
actually	O
exist	O
in	O
the	O
transmitted	O
signal	O
and	O
the	O
envelope	O
of	O
the	O
pulse	O
waveform	O
is	O
extracted	O
from	O
the	O
demodulated	O
carrier	O
in	O
the	O
receiver	O
.	O
</s>
<s>
The	O
pulse	O
width	O
must	O
be	O
long	O
enough	O
to	O
ensure	O
that	O
the	O
radar	B-Application
emits	O
sufficient	O
energy	O
so	O
that	O
the	O
reflected	O
pulse	O
is	O
detectable	O
by	O
its	O
receiver	O
.	O
</s>
<s>
Pulse	O
width	O
also	O
constrains	O
the	O
range	O
discrimination	O
,	O
that	O
is	O
the	O
capacity	O
of	O
the	O
radar	B-Application
to	O
distinguish	O
between	O
two	O
targets	O
that	O
are	O
close	O
together	O
.	O
</s>
<s>
At	O
any	O
range	O
,	O
with	O
similar	O
azimuth	O
and	O
elevation	O
angles	O
and	O
as	O
viewed	O
by	O
a	O
radar	B-Application
with	O
an	O
unmodulated	O
pulse	O
,	O
the	O
range	O
resolution	O
is	O
approximately	O
equal	O
in	O
distance	O
to	O
half	O
of	O
the	O
pulse	O
duration	O
times	O
the	O
speed	O
of	O
light	O
(	O
approximately	O
300	O
meters	O
per	O
microsecond	O
)	O
.	O
</s>
<s>
Pulse	O
width	O
also	O
determines	O
the	O
radar	B-Application
's	O
dead	O
zone	O
at	O
close	O
ranges	O
.	O
</s>
<s>
While	O
the	O
radar	B-Application
transmitter	O
is	O
active	O
,	O
the	O
receiver	O
input	O
is	O
blanked	O
to	O
avoid	O
the	O
amplifiers	O
being	O
swamped	O
(	O
saturated	O
)	O
or	O
,	O
(	O
more	O
likely	O
)	O
,	O
damaged	O
.	O
</s>
<s>
A	O
simple	O
calculation	O
reveals	O
that	O
a	O
radar	B-Application
echo	O
will	O
take	O
approximately	O
10.8μs	O
to	O
return	O
from	O
a	O
target	O
1	O
statute	O
mile	O
away	O
(	O
counting	O
from	O
the	O
leading	O
edge	O
of	O
the	O
transmitter	O
pulse	O
(	O
T0	O
)	O
,	O
(	O
sometimes	O
known	O
as	O
transmitter	O
main	O
bang	O
)	O
)	O
.	O
</s>
<s>
If	O
the	O
radar	B-Application
pulse	O
width	O
is	O
1μs	O
,	O
then	O
there	O
can	O
be	O
no	O
detection	O
of	O
targets	O
closer	O
than	O
about	O
150m	O
,	O
because	O
the	O
receiver	O
is	O
blanked	O
.	O
</s>
<s>
As	O
with	O
everything	O
else	O
in	O
a	O
radar	B-Application
system	I-Application
,	O
compromises	O
have	O
to	O
be	O
made	O
to	O
a	O
radar	B-Application
system	I-Application
's	O
design	O
to	O
provide	O
the	O
optimal	O
performance	O
for	O
its	O
role	O
.	O
</s>
<s>
In	O
order	O
to	O
build	O
up	O
a	O
discernible	O
echo	O
,	O
most	O
radar	B-Application
systems	I-Application
emit	O
pulses	O
continuously	O
and	O
the	O
repetition	O
rate	O
of	O
these	O
pulses	O
is	O
determined	O
by	O
the	O
role	O
of	O
the	O
system	O
.	O
</s>
<s>
However	O
,	O
with	O
the	O
higher	O
PRF	O
the	O
range	O
that	O
the	O
radar	B-Application
can	O
"	O
see	O
"	O
is	O
reduced	O
.	O
</s>
<s>
Radar	B-Application
designers	O
try	O
to	O
use	O
the	O
highest	O
PRF	O
possible	O
commensurate	O
with	O
the	O
other	O
factors	O
that	O
constrain	O
it	O
,	O
as	O
described	O
below	O
.	O
</s>
<s>
There	O
are	O
two	O
other	O
facets	O
related	O
to	O
PRF	O
that	O
the	O
designer	O
must	O
weigh	O
very	O
carefully	O
;	O
the	O
beamwidth	O
characteristics	O
of	O
the	O
antenna	O
,	O
and	O
the	O
required	O
periodicity	O
with	O
which	O
the	O
radar	B-Application
must	O
sweep	O
the	O
field	O
of	O
view	O
.	O
</s>
<s>
A	O
radar	B-Application
with	O
a	O
1°	O
horizontal	O
beamwidth	O
that	O
sweeps	O
the	O
entire	O
360°	O
horizon	O
every	O
2	O
seconds	O
with	O
a	O
PRF	O
of	O
1080Hz	O
will	O
radiate	O
6	O
pulses	O
over	O
each	O
1-degree	O
arc	O
.	O
</s>
<s>
In	O
reality	O
,	O
all	O
three	O
choices	O
are	O
used	O
,	O
to	O
varying	O
extents	O
;	O
radar	B-Application
design	O
is	O
all	O
about	O
compromises	O
between	O
conflicting	O
pressures	O
.	O
</s>
<s>
Staggered	O
PRF	O
is	O
a	O
transmission	O
process	O
where	O
the	O
time	O
between	O
interrogations	O
from	O
radar	B-Application
changes	O
slightly	O
,	O
in	O
a	O
patterned	O
and	O
readily-discernible	O
repeating	O
manner	O
.	O
</s>
<s>
The	O
change	O
of	O
repetition	O
frequency	O
allows	O
the	O
radar	B-Application
,	O
on	O
a	O
pulse-to-pulse	O
basis	O
,	O
to	O
differentiate	O
between	O
returns	O
from	O
its	O
own	O
transmissions	O
and	O
returns	O
from	O
other	O
radar	B-Application
systems	I-Application
with	O
the	O
same	O
PRF	O
and	O
a	O
similar	O
radio	O
frequency	O
.	O
</s>
<s>
Consider	O
a	O
radar	B-Application
with	O
a	O
constant	O
interval	O
between	O
pulses	O
;	O
target	O
reflections	O
appear	O
at	O
a	O
relatively	O
constant	O
range	O
related	O
to	O
the	O
flight-time	O
of	O
the	O
pulse	O
.	O
</s>
<s>
Because	O
their	O
apparent	O
"	O
distance	O
"	O
is	O
defined	O
by	O
measuring	O
their	O
time	O
relative	O
to	O
the	O
last	O
pulse	O
transmitted	O
by	O
"	O
our	O
"	O
radar	B-Application
,	O
these	O
"	O
jamming	O
"	O
pulses	O
could	O
appear	O
at	O
any	O
apparent	O
distance	O
.	O
</s>
<s>
When	O
the	O
PRF	O
of	O
the	O
"	O
jamming	O
"	O
radar	B-Application
is	O
very	O
similar	O
to	O
"	O
our	O
"	O
radar	B-Application
,	O
those	O
apparent	O
distances	O
may	O
be	O
very	O
slow-changing	O
,	O
just	O
like	O
real	O
targets	O
.	O
</s>
<s>
By	O
using	O
stagger	O
,	O
a	O
radar	B-Application
designer	O
can	O
force	O
the	O
"	O
jamming	O
"	O
to	O
jump	O
around	O
erratically	O
in	O
apparent	O
range	O
,	O
inhibiting	O
integration	O
and	O
reducing	O
or	O
even	O
suppressing	O
its	O
impact	O
on	O
true	O
target	O
detection	O
.	O
</s>
<s>
Without	O
staggered	O
PRF	O
,	O
any	O
pulses	O
originating	O
from	O
another	O
radar	B-Application
on	O
the	O
same	O
radio	O
frequency	O
might	O
appear	O
stable	O
in	O
time	O
and	O
could	O
be	O
mistaken	O
for	O
reflections	O
from	O
the	O
radar	B-Application
's	O
own	O
transmission	O
.	O
</s>
<s>
With	O
staggered	O
PRF	O
the	O
radar	B-Application
's	O
own	O
targets	O
appear	O
stable	O
in	O
range	O
in	O
relation	O
to	O
the	O
transmit	O
pulse	O
,	O
whilst	O
the	O
'	O
jamming	O
 '	O
echoes	O
may	O
move	O
around	O
in	O
apparent	O
range	O
(	O
uncorrelated	O
)	O
,	O
causing	O
them	O
to	O
be	O
rejected	O
by	O
the	O
receiver	O
.	O
</s>
<s>
These	O
techniques	O
are	O
in	O
widespread	O
use	O
in	O
marine	O
safety	O
and	O
navigation	O
radars	B-Application
,	O
by	O
far	O
the	O
most	O
numerous	O
radars	B-Application
on	O
planet	O
Earth	O
today	O
.	O
</s>
<s>
Clutter	O
refers	O
to	O
radio	O
frequency	O
(	O
RF	O
)	O
echoes	O
returned	O
from	O
targets	O
which	O
are	O
uninteresting	O
to	O
the	O
radar	B-Application
operators	O
.	O
</s>
<s>
Such	O
targets	O
include	O
natural	O
objects	O
such	O
as	O
ground	O
,	O
sea	O
,	O
precipitation	O
(	O
such	O
as	O
rain	O
,	O
snow	O
or	O
hail	O
)	O
,	O
sand	B-Application
storms	I-Application
,	O
animals	O
(	O
especially	O
birds	O
)	O
,	O
atmospheric	O
turbulence	O
,	O
and	O
other	O
atmospheric	O
effects	O
,	O
such	O
as	O
ionosphere	O
reflections	O
,	O
meteor	B-Language
trails	O
,	O
and	O
three	B-Algorithm
body	I-Algorithm
scatter	I-Algorithm
spike	I-Algorithm
.	O
</s>
<s>
Clutter	O
may	O
also	O
be	O
returned	O
from	O
man-made	O
objects	O
such	O
as	O
buildings	O
and	O
,	O
intentionally	O
,	O
by	O
radar	B-Application
countermeasures	O
such	O
as	O
chaff	O
.	O
</s>
<s>
Some	O
clutter	O
may	O
also	O
be	O
caused	O
by	O
a	O
long	O
radar	B-Application
waveguide	O
between	O
the	O
radar	B-Application
transceiver	O
and	O
the	O
antenna	O
.	O
</s>
<s>
In	O
a	O
typical	O
plan	B-Algorithm
position	I-Algorithm
indicator	I-Algorithm
(	O
PPI	O
)	O
radar	B-Application
with	O
a	O
rotating	O
antenna	O
,	O
this	O
will	O
usually	O
be	O
seen	O
as	O
a	O
"	O
sun	O
"	O
or	O
"	O
sunburst	O
"	O
in	O
the	O
centre	O
of	O
the	O
display	O
as	O
the	O
receiver	O
responds	O
to	O
echoes	O
from	O
dust	O
particles	O
and	O
misguided	O
RF	O
in	O
the	O
waveguide	O
.	O
</s>
<s>
Clutter	O
is	O
considered	O
a	O
passive	O
interference	O
source	O
,	O
since	O
it	O
only	O
appears	O
in	O
response	O
to	O
radar	B-Application
signals	O
sent	O
by	O
the	O
radar	B-Application
.	O
</s>
<s>
Clutter	O
tends	O
to	O
appear	O
static	O
between	O
radar	B-Application
scans	O
;	O
on	O
subsequent	O
scan	O
echoes	O
,	O
desirable	O
targets	O
will	O
appear	O
to	O
move	O
,	O
and	O
all	O
stationary	O
echoes	O
can	O
be	O
eliminated	O
.	O
</s>
<s>
Sea	O
clutter	O
can	O
be	O
reduced	O
by	O
using	O
horizontal	O
polarization	O
,	O
while	O
rain	O
is	O
reduced	O
with	O
circular	O
polarization	O
(	O
note	O
that	O
meteorological	B-Application
radars	I-Application
wish	O
for	O
the	O
opposite	O
effect	O
,	O
and	O
therefore	O
use	O
linear	O
polarization	O
to	O
detect	O
precipitation	O
)	O
.	O
</s>
<s>
The	O
most	O
effective	O
clutter	O
reduction	O
technique	O
is	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
with	O
Look-down/shoot	O
-down	O
capability	O
.	O
</s>
<s>
This	O
can	O
be	O
adapted	O
for	O
systems	O
that	O
lack	O
a	O
coherent	O
transmitter	O
,	O
such	O
as	O
time-domain	O
pulse-amplitude	O
radar	B-Application
.	O
</s>
<s>
Constant	B-Algorithm
False	I-Algorithm
Alarm	I-Algorithm
Rate	I-Algorithm
,	O
a	O
form	O
of	O
Automatic	O
Gain	O
Control	O
(	O
AGC	O
)	O
,	O
is	O
a	O
method	O
that	O
relies	O
on	O
clutter	O
returns	O
far	O
outnumbering	O
echoes	O
from	O
targets	O
of	O
interest	O
.	O
</s>
<s>
In	O
the	O
past	O
,	O
radar	B-Application
AGC	O
was	O
electronically	O
controlled	O
and	O
affected	O
the	O
gain	O
of	O
the	O
entire	O
radar	B-Application
receiver	O
.	O
</s>
<s>
As	O
radars	B-Application
evolved	O
,	O
AGC	O
became	O
computer-software	O
controlled	O
and	O
affected	O
the	O
gain	O
with	O
greater	O
granularity	O
in	O
specific	O
detection	O
cells	O
.	O
</s>
<s>
Clutter	O
may	O
also	O
originate	O
from	O
multipath	O
echoes	O
from	O
valid	O
targets	O
caused	O
by	O
ground	O
reflection	O
,	O
atmospheric	O
ducting	O
or	O
ionospheric	O
reflection/refraction	O
(	O
e.g.	O
,	O
Anomalous	B-Algorithm
propagation	I-Algorithm
)	O
.	O
</s>
<s>
The	O
radar	B-Application
may	O
try	O
to	O
unify	O
the	O
targets	O
,	O
reporting	O
the	O
target	O
at	O
an	O
incorrect	O
height	O
,	O
or	O
eliminating	O
it	O
on	O
the	O
basis	O
of	O
jitter	O
or	O
a	O
physical	O
impossibility	O
.	O
</s>
<s>
Terrain	O
bounce	O
jamming	O
exploits	O
this	O
response	O
by	O
amplifying	O
the	O
radar	B-Application
signal	O
and	O
directing	O
it	O
downward	O
.	O
</s>
<s>
These	O
problems	O
can	O
be	O
overcome	O
by	O
incorporating	O
a	O
ground	O
map	O
of	O
the	O
radar	B-Application
's	O
surroundings	O
and	O
eliminating	O
all	O
echoes	O
which	O
appear	O
to	O
originate	O
below	O
ground	O
or	O
above	O
a	O
certain	O
height	O
.	O
</s>
<s>
In	O
newer	O
air	O
traffic	O
control	O
radar	B-Application
equipment	O
,	O
algorithms	O
are	O
used	O
to	O
identify	O
the	O
false	O
targets	O
by	O
comparing	O
the	O
current	O
pulse	O
returns	O
to	O
those	O
adjacent	O
,	O
as	O
well	O
as	O
calculating	O
return	O
improbabilities	O
.	O
</s>
<s>
STC	B-Algorithm
is	O
used	O
to	O
avoid	O
saturation	O
of	O
the	O
receiver	O
from	O
close	O
in	O
ground	O
clutter	O
by	O
adjusting	O
the	O
attenuation	O
of	O
the	O
receiver	O
as	O
a	O
function	O
of	O
distance	O
.	O
</s>
<s>
Consider	O
the	O
following	O
example	O
:	O
if	O
the	O
radar	B-Application
antenna	O
is	O
located	O
at	O
around	O
15	O
m	O
above	O
sea	O
level	O
,	O
then	O
the	O
distance	O
to	O
the	O
horizon	O
is	O
pretty	O
close	O
,	O
(	O
perhaps	O
15km	O
)	O
.	O
</s>
<s>
Ground	O
targets	O
further	O
than	O
this	O
range	O
cannot	O
be	O
detected	O
,	O
so	O
the	O
PRF	O
can	O
be	O
quite	O
high	O
;	O
a	O
radar	B-Application
with	O
a	O
PRF	O
of	O
7.5kHz	O
will	O
return	O
ambiguous	O
echoes	O
from	O
targets	O
at	O
about	O
20km	O
,	O
or	O
over	O
the	O
horizon	O
.	O
</s>
<s>
If	O
a	O
longer	O
unambiguous	O
range	O
is	O
required	O
with	O
this	O
simple	O
system	O
,	O
then	O
lower	O
PRFs	O
are	O
required	O
and	O
it	O
was	O
quite	O
common	O
for	O
early	O
search	O
radars	B-Application
to	O
have	O
PRFs	O
as	O
low	O
as	O
a	O
few	O
hundred	O
Hz	O
,	O
giving	O
an	O
unambiguous	O
range	O
out	O
to	O
well	O
in	O
excess	O
of	O
150km	O
.	O
</s>
<s>
However	O
,	O
lower	O
PRFs	O
introduce	O
other	O
problems	O
,	O
including	O
poorer	O
target	O
painting	O
and	O
velocity	O
ambiguity	O
in	O
Pulse-Doppler	B-Algorithm
systems	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
Modern	O
radars	B-Application
,	O
especially	O
air-to-air	O
combat	O
radars	B-Application
in	O
military	O
aircraft	O
,	O
may	O
use	O
PRFs	O
in	O
the	O
tens-to-hundreds	O
of	O
kilohertz	O
and	O
stagger	O
the	O
interval	O
between	O
pulses	O
to	O
allow	O
the	O
correct	O
range	O
to	O
be	O
determined	O
.	O
</s>
<s>
Such	O
radars	B-Application
may	O
use	O
repetitive	O
patterns	O
of	O
packets	O
,	O
or	O
more	O
adaptable	O
packets	O
that	O
respond	O
to	O
apparent	O
target	O
behaviors	O
.	O
</s>
<s>
Regardless	O
,	O
radars	B-Application
that	O
employ	O
the	O
technique	O
are	O
universally	O
coherent	O
,	O
with	O
a	O
very	O
stable	O
radio	O
frequency	O
,	O
and	O
the	O
pulse	O
packets	O
may	O
also	O
be	O
used	O
to	O
make	O
measurements	O
of	O
the	O
Doppler	O
shift	O
(	O
a	O
velocity-dependent	O
modification	O
of	O
the	O
apparent	O
radio	O
frequency	O
)	O
,	O
especially	O
when	O
the	O
PRFs	O
are	O
in	O
the	O
hundreds-of-kilohertz	O
range	O
.	O
</s>
<s>
Radars	B-Application
exploiting	O
Doppler	O
effects	O
in	O
this	O
manner	O
typically	O
determine	O
relative	O
velocity	O
first	O
,	O
from	O
the	O
Doppler	O
effect	O
,	O
and	O
then	O
use	O
other	O
techniques	O
to	O
derive	O
target	O
distance	O
.	O
</s>
<s>
A	O
civil	O
marine	O
radar	B-Application
,	O
for	O
instance	O
,	O
may	O
have	O
user-selectable	O
maximum	O
instrumented	O
display	O
ranges	O
of	O
72	O
,	O
or	O
96	O
or	O
rarely	O
120	O
nautical	O
miles	O
,	O
in	O
accordance	O
with	O
international	O
law	O
,	O
but	O
maximum	O
unambiguous	O
ranges	O
of	O
over	O
40,000	O
nautical	O
miles	O
and	O
maximum	O
detection	O
ranges	O
of	O
perhaps	O
150	O
nautical	O
miles	O
.	O
</s>
<s>
Pure	O
CW	B-Algorithm
radars	I-Algorithm
appear	O
as	O
a	O
single	O
line	O
on	O
a	O
Spectrum	O
analyser	O
display	O
and	O
when	O
modulated	B-Application
with	O
other	O
sinusoidal	O
signals	O
,	O
the	O
spectrum	O
differs	O
little	O
from	O
that	O
obtained	O
with	O
standard	O
analogue	B-Application
modulation	I-Application
schemes	O
used	O
in	O
communications	O
systems	O
,	O
such	O
as	O
Frequency	B-Application
Modulation	I-Application
and	O
consist	O
of	O
the	O
carrier	O
plus	O
a	O
relatively	O
small	O
number	O
of	O
sidebands	O
.	O
</s>
<s>
When	O
the	O
radar	B-Application
signal	O
is	O
modulated	B-Application
with	O
a	O
pulse	O
train	O
as	O
shown	O
above	O
,	O
the	O
spectrum	O
becomes	O
much	O
more	O
complicated	O
and	O
far	O
more	O
difficult	O
to	O
visualise	O
.	O
</s>
<s>
The	O
radar	B-Application
pulse	O
train	O
is	O
a	O
form	O
of	O
square	O
wave	O
,	O
the	O
pure	O
form	O
of	O
which	O
consists	O
of	O
the	O
fundamental	O
plus	O
all	O
of	O
the	O
odd	O
harmonics	O
.	O
</s>
<s>
When	O
the	O
pulse	O
train	O
is	O
used	O
to	O
modulate	O
a	O
radar	B-Application
carrier	O
,	O
the	O
typical	O
spectrum	O
shown	O
on	O
the	O
left	O
will	O
be	O
obtained	O
.	O
</s>
<s>
These	O
facts	O
affect	O
the	O
decisions	O
made	O
by	O
radar	B-Application
designers	O
when	O
considering	O
the	O
trade-offs	O
that	O
need	O
to	O
be	O
made	O
when	O
trying	O
to	O
overcome	O
the	O
ambiguities	O
that	O
affect	O
radar	B-Application
signals	O
.	O
</s>
<s>
If	O
the	O
rise	O
and	O
fall	O
times	O
of	O
the	O
modulation	B-Application
pulses	O
are	O
zero	O
,	O
(	O
e.g.	O
</s>
<s>
Early	O
radars	B-Application
limited	O
the	O
bandwidth	O
through	O
filtration	O
in	O
the	O
transmit	O
chain	O
,	O
e.g.	O
</s>
<s>
Further	O
examination	O
of	O
the	O
basic	O
Radar	B-Application
Spectrum	O
shown	O
above	O
shows	O
that	O
the	O
information	O
in	O
the	O
various	O
lobes	O
of	O
the	O
Coarse	O
Spectrum	O
is	O
identical	O
to	O
that	O
contained	O
in	O
the	O
main	O
lobe	O
,	O
so	O
limiting	O
the	O
transmit	O
and	O
receive	O
bandwidth	O
to	O
that	O
extent	O
provides	O
significant	O
benefits	O
in	O
terms	O
of	O
efficiency	O
and	O
noise	O
reduction	O
.	O
</s>
<s>
When	O
this	O
technique	O
is	O
combined	O
with	O
pulse	B-Algorithm
compression	I-Algorithm
,	O
then	O
a	O
good	O
compromise	O
between	O
efficiency	O
,	O
performance	O
and	O
range	O
resolution	O
can	O
be	O
realised	O
.	O
</s>
<s>
This	O
is	O
an	O
issue	O
only	O
with	O
a	O
particular	O
type	O
of	O
system	O
;	O
the	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
,	O
which	O
uses	O
the	O
Doppler	O
effect	O
to	O
resolve	O
velocity	O
from	O
the	O
apparent	O
change	O
in	O
frequency	O
caused	O
by	O
targets	O
that	O
have	O
net	O
radial	O
velocities	O
compared	O
to	O
the	O
radar	B-Application
device	O
.	O
</s>
<s>
It	O
can	O
be	O
seen	O
that	O
as	O
the	O
relative	O
velocity	O
increases	O
,	O
a	O
point	O
will	O
be	O
reached	O
where	O
the	O
spectral	O
lines	O
that	O
constitute	O
the	O
echoes	O
are	O
hidden	O
or	O
aliased	B-Error_Name
by	O
the	O
next	O
sideband	O
of	O
the	O
modulated	B-Application
carrier	O
.	O
</s>
<s>
Taking	O
all	O
of	O
the	O
above	O
characteristics	O
into	O
account	O
means	O
that	O
certain	O
constraints	O
are	O
placed	O
on	O
the	O
radar	B-Application
designer	O
.	O
</s>
