<s>
An	O
airport	O
surveillance	O
radar	B-Application
(	O
ASR	O
)	O
is	O
a	O
radar	B-Application
system	I-Application
used	O
at	O
airports	O
to	O
detect	O
and	O
display	O
the	O
presence	O
and	O
position	O
of	O
aircraft	O
in	O
the	O
terminal	O
area	O
,	O
the	O
airspace	O
around	O
airports	O
.	O
</s>
<s>
It	O
is	O
the	O
main	O
air	B-Application
traffic	I-Application
control	I-Application
system	I-Application
for	O
the	O
airspace	O
around	O
airports	O
.	O
</s>
<s>
The	O
sophisticated	O
systems	O
at	O
large	O
airports	O
consist	O
of	O
two	O
different	O
radar	B-Application
systems	I-Application
,	O
the	O
primary	O
and	O
secondary	O
surveillance	O
radar	B-Application
.	O
</s>
<s>
The	O
primary	O
radar	B-Application
typically	O
consists	O
of	O
a	O
large	O
rotating	O
parabolic	O
antenna	O
dish	O
that	O
sweeps	O
a	O
vertical	O
fan-shaped	O
beam	O
of	O
microwaves	O
around	O
the	O
airspace	O
surrounding	O
the	O
airport	O
.	O
</s>
<s>
The	O
secondary	O
surveillance	O
radar	B-Application
consists	O
of	O
a	O
second	O
rotating	O
antenna	O
,	O
often	O
mounted	O
on	O
the	O
primary	O
antenna	O
,	O
which	O
interrogates	O
the	O
transponders	B-Architecture
of	O
aircraft	O
,	O
which	O
transmits	O
a	O
radio	O
signal	O
back	O
containing	O
the	O
aircraft	O
's	O
identification	O
,	O
barometric	O
altitude	O
,	O
and	O
an	O
emergency	O
status	O
code	O
,	O
which	O
is	O
displayed	O
on	O
the	O
radar	B-Application
screen	O
next	O
to	O
the	O
return	O
from	O
the	O
primary	O
radar	B-Application
.	O
</s>
<s>
The	O
positions	O
of	O
the	O
aircraft	O
are	O
displayed	O
on	O
a	O
screen	O
;	O
at	O
large	O
airports	O
on	O
multiple	O
screens	O
in	O
an	O
operations	O
room	O
at	O
the	O
airport	O
called	O
in	O
the	O
US	O
the	O
Terminal	B-Application
Radar	I-Application
Approach	I-Application
Control	I-Application
(	O
TRACON	O
)	O
,	O
monitored	O
by	O
air	B-Application
traffic	I-Application
controllers	I-Application
who	O
direct	O
the	O
traffic	O
by	O
communicating	O
with	O
the	O
aircraft	O
pilots	O
by	O
radio	O
.	O
</s>
<s>
Radar	B-Application
was	O
developed	O
during	O
World	O
War	O
II	O
as	O
a	O
military	O
air	O
defense	O
system	O
.	O
</s>
<s>
The	O
primary	O
surveillance	O
radar	B-Application
(	O
PSR	O
)	O
consists	O
of	O
a	O
large	O
parabolic	O
"	O
dish	O
"	O
antenna	O
mounted	O
on	O
a	O
tower	O
so	O
it	O
can	O
scan	O
the	O
entire	O
airspace	O
unobstructed	O
.	O
</s>
<s>
In	O
the	O
US	O
the	O
primary	O
radar	B-Application
operates	O
at	O
a	O
frequency	O
of	O
2.7	O
-	O
2.9GHz	O
in	O
the	B-Algorithm
S	I-Algorithm
band	I-Algorithm
with	O
a	O
peak	O
radiated	O
power	O
of	O
25kW	O
and	O
an	O
average	O
power	O
of	O
2.1kW	O
.	O
</s>
<s>
When	O
the	O
microwave	O
beam	O
strikes	O
an	O
airborne	O
object	O
,	O
the	O
microwaves	O
are	O
reflected	O
and	O
some	O
of	O
the	O
energy	O
(	O
sometimes	O
called	O
the	O
"	O
echo	O
"	O
)	O
returns	O
to	O
the	O
dish	O
and	O
is	O
detected	O
by	O
the	O
radar	B-Application
receiver	O
.	O
</s>
<s>
Since	O
the	O
microwaves	O
travel	O
at	O
a	O
constant	O
speed	O
very	O
close	O
to	O
the	O
speed	O
of	O
light	O
,	O
by	O
timing	O
the	O
brief	O
interval	O
between	O
the	O
transmitted	O
pulse	O
and	O
the	O
returning	O
"	O
echo	O
"	O
the	O
radar	B-Application
can	O
calculate	O
the	O
range	O
from	O
the	O
antenna	O
to	O
the	O
object	O
.	O
</s>
<s>
The	O
location	O
of	O
the	O
object	O
is	O
displayed	O
as	O
an	O
icon	O
on	O
a	O
map	O
display	O
called	O
a	O
"	O
radar	B-Application
screen	O
"	O
.	O
</s>
<s>
The	O
screen	O
may	O
be	O
located	O
in	O
the	O
control	O
tower	O
,	O
or	O
at	O
large	O
airports	O
on	O
multiple	O
screens	O
in	O
an	O
operations	O
room	O
at	O
the	O
airport	O
called	O
in	O
the	O
US	O
the	O
Terminal	B-Application
Radar	I-Application
Approach	I-Application
Control	I-Application
(	O
TRACON	O
)	O
.	O
</s>
<s>
The	O
primary	O
radar	B-Application
's	O
main	O
function	O
is	O
to	O
determine	O
the	O
location	O
,	O
the	O
bearing	O
and	O
range	O
to	O
the	O
aircraft	O
.	O
</s>
<s>
Air	B-Application
traffic	I-Application
controllers	I-Application
continuously	O
monitor	O
the	O
positions	O
of	O
all	O
the	O
aircraft	O
on	O
the	O
radar	B-Application
screen	O
,	O
and	O
give	O
directions	O
to	O
the	O
pilots	O
by	O
radio	O
to	O
maintain	O
a	O
safe	O
and	O
orderly	O
flow	O
of	O
air	B-Application
traffic	I-Application
in	O
the	O
airspace	O
.	O
</s>
<s>
The	O
need	O
for	O
a	O
secondary	O
radar	B-Application
system	I-Application
developed	O
from	O
the	O
limitations	O
of	O
primary	O
radar	B-Application
and	O
need	O
for	O
more	O
information	O
by	O
air	B-Application
traffic	I-Application
controllers	I-Application
due	O
to	O
the	O
increasing	O
postwar	O
volume	O
of	O
air	B-Application
traffic	I-Application
.	O
</s>
<s>
The	O
primary	O
radar	B-Application
displays	O
a	O
"	O
return	O
"	O
indiscriminately	O
from	O
any	O
object	O
in	O
its	O
field	O
of	O
view	O
,	O
and	O
cannot	O
distinguish	O
between	O
aircraft	O
,	O
drones	O
,	O
weather	O
balloons	O
,	O
birds	O
,	O
and	O
some	O
elevated	O
features	O
of	O
the	O
terrain	O
(	O
called	O
"	O
ground	O
clutter	O
"	O
)	O
.	O
</s>
<s>
Primary	O
radar	B-Application
also	O
cannot	O
identify	O
an	O
aircraft	O
;	O
before	O
secondary	O
radar	B-Application
aircraft	O
were	O
identified	O
by	O
the	O
controller	O
asking	O
the	O
aircraft	O
by	O
radio	O
to	O
waggle	O
its	O
wings	O
.	O
</s>
<s>
Another	O
limitation	O
is	O
that	O
primary	O
radar	B-Application
cannot	O
determine	O
the	O
altitude	O
of	O
the	O
aircraft	O
.	O
</s>
<s>
Secondary	O
surveillance	O
radar	B-Application
(	O
SSR	O
)	O
,	O
also	O
called	O
the	O
air	B-Application
traffic	I-Application
control	I-Application
radar	I-Application
beacon	I-Application
system	I-Application
(	O
ATCRBS	B-Application
)	O
had	O
its	O
origin	O
in	O
Identification	B-Device
Friend	I-Device
or	I-Device
Foe	I-Device
(	O
IFF	O
)	O
systems	O
used	O
by	O
military	O
aircraft	O
during	O
World	O
War	O
II	O
.	O
</s>
<s>
All	O
aircraft	O
are	O
required	O
to	O
carry	O
an	O
automated	O
microwave	O
transceiver	O
called	O
a	O
transponder	B-Architecture
.	O
</s>
<s>
The	O
secondary	O
radar	B-Application
is	O
a	O
rotating	O
flat	O
antenna	O
,	O
often	O
mounted	O
on	O
top	O
of	O
the	O
primary	O
radar	B-Application
dish	O
,	O
which	O
transmits	O
a	O
narrow	O
vertical	O
fan-shaped	O
microwave	O
beam	O
on	O
a	O
frequency	O
of	O
1030MHz	O
in	O
the	O
L	B-Algorithm
band	I-Algorithm
with	O
peak	O
power	O
of	O
160	O
-	O
1500	O
W	O
.	O
When	O
it	O
is	O
interrogated	O
by	O
this	O
signal	O
,	O
the	O
aircraft	O
's	O
transponder	B-Architecture
beacon	O
transmits	O
a	O
coded	O
identifying	O
microwave	O
signal	O
at	O
a	O
frequency	O
of	O
1090MHz	O
back	O
to	O
the	O
secondary	O
radar	B-Application
antenna	O
.	O
</s>
<s>
This	O
coded	O
signal	O
includes	O
a	O
4	O
digit	O
number	O
called	O
the	O
"	O
transponder	B-Architecture
code	O
"	O
which	O
identifies	O
the	O
aircraft	O
,	O
and	O
the	O
aircraft	O
's	O
pressure	O
altitude	O
from	O
the	O
pilot	O
's	O
altimeter	O
.	O
</s>
<s>
This	O
information	O
is	O
displayed	O
on	O
the	O
radar	B-Application
screen	O
beside	O
the	O
aircraft	O
's	O
icon	O
for	O
use	O
by	O
the	O
air	B-Application
traffic	I-Application
controller	I-Application
.	O
</s>
<s>
The	O
transponder	B-Architecture
code	O
is	O
assigned	O
to	O
the	O
aircraft	O
by	O
the	O
air	B-Application
traffic	I-Application
controller	I-Application
before	O
takeoff	O
.	O
</s>
<s>
Controllers	O
use	O
the	O
term	O
"	O
squawk	O
"	O
when	O
they	O
are	O
assigning	O
a	O
transponder	B-Architecture
code	O
,	O
e.g.	O
,	O
"	O
Squawk	O
7421	O
"	O
.	O
</s>
<s>
Transponders	B-Architecture
can	O
respond	O
with	O
one	O
of	O
several	O
different	O
"	O
modes	O
"	O
determined	O
by	O
the	O
interrogation	O
pulse	O
from	O
the	O
radar	B-Application
.	O
</s>
<s>
Only	O
Mode	B-Architecture
C	I-Architecture
transponders	B-Architecture
report	O
altitude	O
.	O
</s>
<s>
Busy	O
airports	O
usually	O
require	O
all	O
aircraft	O
entering	O
their	O
airspace	O
to	O
have	O
a	O
mode	B-Architecture
C	I-Architecture
transponder	B-Architecture
which	O
can	O
report	O
altitude	O
,	O
due	O
to	O
their	O
strict	O
requirements	O
for	O
aircraft	O
altitude	O
spacing	O
;	O
this	O
is	O
called	O
a	O
"	O
Mode	B-Architecture
C	I-Architecture
veil	O
"	O
.	O
</s>
<s>
Due	O
to	O
its	O
crucial	O
safety	O
mission	O
,	O
extreme	O
uptime	O
requirements	O
,	O
and	O
need	O
to	O
be	O
compatible	O
with	O
all	O
the	O
different	O
types	O
of	O
aircraft	O
and	O
avionics	O
systems	O
,	O
the	O
design	O
of	O
airport	O
surveillance	O
radar	B-Application
is	O
strictly	O
controlled	O
by	O
government	O
agencies	O
.	O
</s>
<s>
In	O
the	O
US	O
the	O
Federal	O
Aviation	O
Administration	O
(	O
FAA	O
)	O
is	O
responsible	O
for	O
developing	O
airport	O
surveillance	O
radar	B-Application
.	O
</s>
<s>
The	O
military	O
nomenclature	O
for	O
the	O
radar	B-Application
is	O
AN/GPN	O
-20	O
.	O
</s>
<s>
It	O
is	O
an	O
aging	O
radar	B-Application
system	I-Application
that	O
is	O
obsolete	O
,	O
not	O
logistically	O
supported	O
,	O
does	O
not	O
provide	O
digital	O
inputs	O
to	O
new	O
terminal	O
automation	O
systems	O
,	O
and	O
does	O
not	O
provide	O
a	O
calibrated	O
precipitation	O
intensity	O
product	O
nor	O
any	O
storm	O
motion	O
information	O
.	O
</s>
<s>
It	O
is	O
a	O
relocatable	O
,	O
solid-state	O
,	O
all-weather	O
radar	B-Application
with	O
dual-channel	O
,	O
frequency	O
diversity	O
,	O
remote	O
operator	O
controls	O
,	O
and	O
a	O
dual	O
beam	O
tower	O
mounted	O
antenna	O
.	O
</s>
<s>
The	O
radar	B-Application
provides	O
controllers	O
with	O
range	O
azimuth	O
of	O
aircraft	O
within	O
a	O
60	O
nautical	O
mile	O
radius	O
.	O
</s>
<s>
The	O
US	O
Army/Navy	O
designator	O
AN/GPN	O
-20	O
refers	O
to	O
a	O
modified	O
version	O
of	O
the	O
ASR	O
8	O
used	O
by	O
the	O
USAF	O
containing	O
a	O
magnetron	B-Device
tube	O
as	O
transmitter	O
.	O
</s>
<s>
To	O
improve	O
the	O
magnetron	B-Device
's	O
frequency	O
stability	O
the	O
magnetron	B-Device
tuning	O
is	O
driven	O
by	O
the	O
AFC	O
.	O
</s>
<s>
The	O
current	O
generation	O
of	O
radar	B-Application
is	O
the	O
ASR-9	B-Algorithm
,	O
which	O
was	O
developed	O
by	O
Westinghouse	O
Electric	O
Corporation	O
and	O
first	O
installed	O
in	O
1989	O
,	O
with	O
installation	O
completing	O
in	O
1995	O
.	O
</s>
<s>
The	O
military	O
nomenclature	O
for	O
the	O
radar	B-Application
is	O
AN/GPN	O
-27	O
.	O
</s>
<s>
The	O
ASR-9	B-Algorithm
was	O
the	O
first	O
airport	O
surveillance	O
radar	B-Application
to	O
detect	O
weather	O
and	O
aircraft	O
with	O
the	O
same	O
beam	O
and	O
be	O
able	O
to	O
display	O
them	O
on	O
the	O
same	O
screen	O
.	O
</s>
<s>
It	O
has	O
a	O
digital	O
Moving	O
Target	O
Detection	O
(	O
MTD	O
)	O
processor	O
which	O
uses	O
doppler	B-Algorithm
radar	I-Algorithm
and	O
a	O
clutter	O
map	O
giving	O
advanced	O
ability	O
to	O
eliminate	O
ground	O
and	O
weather	O
clutter	O
and	O
track	O
targets	O
.	O
</s>
<s>
The	O
klystron	O
tube	O
transmitter	O
operates	O
in	O
the	O
S-band	B-Algorithm
between	O
2.5	O
and	O
2.9GHz	O
in	O
circular	O
polarization	O
with	O
a	O
peak	O
power	O
of	O
1.3MW	O
and	O
a	O
pulse	O
duration	O
of	O
1μs	O
and	O
pulse	O
repetition	O
frequency	O
between	O
325	O
and	O
1200	O
pps	O
.	O
</s>
<s>
The	O
receiver	O
has	O
the	O
sensitivity	O
to	O
detect	O
a	O
radar	B-Application
cross-section	O
of	O
1	O
meter2	O
at	O
111km	O
,	O
and	O
a	O
range	O
resolution	O
of	O
450	O
feet	O
.	O
</s>
<s>
Like	O
all	O
airport	O
surveillance	O
radars	B-Application
it	O
has	O
a	O
backup	O
diesel	O
generator	O
to	O
continue	O
operating	O
during	O
power	O
outages	O
.	O
</s>
<s>
The	O
Digital	O
Airport	O
Surveillance	O
Radar	B-Application
(	O
DASR	O
)	O
is	O
the	O
new	O
generation	O
of	O
fully	O
digital	O
radar	B-Application
that	O
is	O
being	O
developed	O
to	O
replace	O
the	O
current	O
analog	O
systems	O
.	O
</s>
<s>
The	O
US	O
Air	O
Force	O
Electronics	O
Systems	O
Center	O
,	O
the	O
US	O
Federal	O
Aviation	O
Administration	O
,	O
US	O
Army	O
and	O
the	O
US	O
Navy	O
procured	O
DASR	O
systems	O
to	O
upgrade	O
existing	O
radar	B-Application
facilities	O
for	O
US	O
Department	O
of	O
Defense	O
(	O
DoD	O
)	O
and	O
civilian	O
airfields	O
.	O
</s>
<s>
The	O
civilian	O
nomenclature	O
for	O
this	O
radar	B-Application
is	O
ASR-11	B-Algorithm
.	O
</s>
<s>
The	O
ASR-11	B-Algorithm
will	O
replace	O
most	O
ASR-7	O
and	O
some	O
ASR-8	O
.	O
</s>
<s>
The	O
military	O
nomenclature	O
for	O
the	O
radar	B-Application
is	O
AN/GPN	B-Algorithm
-30	I-Algorithm
.	O
</s>
<s>
The	O
older	O
radars	B-Application
,	O
some	O
up	O
to	O
20	O
years	O
old	O
,	O
are	O
being	O
replaced	O
to	O
improve	O
reliability	O
,	O
provide	O
additional	O
weather	O
data	O
,	O
reduce	O
maintenance	O
cost	O
,	O
improve	O
performance	O
,	O
and	O
provide	O
digital	O
data	O
to	O
new	O
digital	O
automation	O
systems	O
for	O
presentation	O
on	O
air	B-Application
traffic	I-Application
control	I-Application
displays	O
.	O
</s>
<s>
ASR	O
data	O
is	O
displayed	O
on	O
Standard	O
Terminal	O
Automation	O
Replacement	O
System	O
(	O
STARS	O
)	O
display	O
consoles	O
in	O
control	O
towers	O
and	O
Terminal	B-Application
Radar	I-Application
Approach	I-Application
Control	I-Application
(	O
TRACON	O
)	O
rooms	O
,	O
usually	O
located	O
at	O
airports	O
.	O
</s>
<s>
The	O
Standard	O
Terminal	O
Automation	O
Replacement	O
System	O
(	O
STARS	O
)	O
is	O
a	O
joint	O
Federal	O
Aviation	O
Administration	O
(	O
FAA	O
)	O
and	O
Department	O
of	O
Defense	O
(	O
DoD	O
)	O
program	O
that	O
has	O
replaced	O
Automated	O
Radar	B-Application
Terminal	O
Systems	O
(	O
ARTS	O
)	O
and	O
other	O
capacity-constrained	O
,	O
older	O
technology	O
systems	O
at	O
172	O
FAA	O
and	O
up	O
to	O
199	O
DoD	O
terminal	B-Application
radar	I-Application
approach	I-Application
control	I-Application
facilities	O
and	O
associated	O
towers	O
.	O
</s>
<s>
STARS	O
is	O
used	O
by	O
controllers	O
,	O
at	O
all	O
terminal	O
radar	B-Application
facilities	O
in	O
the	O
US	O
to	O
provide	O
air	B-Application
traffic	I-Application
control	I-Application
(	O
ATC	B-Application
)	O
services	O
to	O
aircraft	O
in	O
the	O
terminal	O
areas	O
.	O
</s>
<s>
Typical	O
terminal	O
area	O
ATC	B-Application
services	O
are	O
defined	O
as	O
the	O
area	O
around	O
airports	O
where	O
departing	O
and	O
arriving	O
traffic	O
are	O
served	O
.	O
</s>
<s>
Functions	O
include	O
aircraft	O
separation	O
,	O
weather	O
advisories	O
,	O
and	O
lower	O
level	O
control	O
of	O
air	B-Application
traffic	I-Application
.	O
</s>
<s>
The	O
system	O
is	O
designed	O
to	O
accommodate	O
air	B-Application
traffic	I-Application
growth	O
and	O
the	O
introduction	O
of	O
new	O
automation	O
functions	O
which	O
will	O
improve	O
the	O
safety	O
and	O
efficiency	O
of	O
the	O
US	O
National	O
Airspace	O
System	O
(	O
NAS	O
)	O
.	O
</s>
<s>
Airport	O
Surveillance	O
Radar	B-Application
is	O
beginning	O
to	O
be	O
supplemented	O
by	O
ADS-B	B-Application
Automatic	B-Application
dependent	I-Application
surveillance-broadcast	I-Application
in	O
the	O
US	O
and	O
other	O
parts	O
of	O
the	O
world	O
.	O
</s>
<s>
As	O
of	O
Spring	O
2011	O
,	O
ADS-B	B-Application
is	O
currently	O
operational	O
at	O
most	O
ATC	B-Application
facilities	O
in	O
the	O
US	O
.	O
</s>
<s>
ADS-B	B-Application
is	O
a	O
GPS	O
based	O
technology	O
that	O
allows	O
aircraft	O
to	O
transmit	O
their	O
GPS	O
determined	O
position	O
to	O
display	O
systems	O
as	O
often	O
as	O
once	O
per	O
second	O
,	O
as	O
opposed	O
to	O
once	O
every	O
5	O
–	O
6	O
seconds	O
for	O
a	O
short	O
range	O
radar	B-Application
,	O
or	O
once	O
every	O
12	O
–	O
13	O
seconds	O
for	O
a	O
slower	O
rotating	O
long	O
range	O
radar	B-Application
.	O
</s>
<s>
The	O
FAA	O
is	O
mandating	O
that	O
ADS-B	B-Application
be	O
fully	O
operational	O
and	O
available	O
to	O
the	O
NAS	O
by	O
the	O
year	O
2020	O
.	O
</s>
<s>
This	O
will	O
make	O
possible	O
the	O
decommissioning	O
of	O
older	O
radars	B-Application
in	O
order	O
to	O
increase	O
safety	O
and	O
cut	O
costs	O
.	O
</s>
<s>
As	O
of	O
2011	O
,	O
there	O
is	O
no	O
definitive	O
list	O
of	O
radars	B-Application
that	O
will	O
be	O
decommissioned	O
as	O
a	O
result	O
of	O
ADS-B	B-Application
implementation	O
.	O
</s>
