<s>
In	O
antenna	O
theory	O
,	O
a	O
phased	O
array	O
usually	O
means	O
an	O
electronically	O
scanned	O
array	O
,	O
a	O
computer-controlled	O
array	B-Algorithm
of	I-Algorithm
antennas	I-Algorithm
which	O
creates	O
a	O
beam	O
of	O
radio	O
waves	O
that	O
can	O
be	O
electronically	O
steered	O
to	O
point	O
in	O
different	O
directions	O
without	O
moving	O
the	O
antennas	O
.	O
</s>
<s>
In	O
a	O
simple	O
array	B-Algorithm
antenna	I-Algorithm
,	O
the	O
radio	O
frequency	O
current	O
from	O
the	O
transmitter	O
is	O
fed	O
to	O
multiple	O
individual	O
antenna	O
elements	O
with	O
the	O
proper	O
phase	O
relationship	O
so	O
that	O
the	O
radio	O
waves	O
from	O
the	O
separate	O
elements	O
combine	O
(	O
superpose	O
)	O
to	O
form	O
beams	O
,	O
to	O
increase	O
power	O
radiated	O
in	O
desired	O
directions	O
and	O
suppress	O
radiation	O
in	O
undesired	O
directions	O
.	O
</s>
<s>
In	O
a	O
phased	O
array	O
,	O
the	O
power	O
from	O
the	O
transmitter	O
is	O
fed	O
to	O
the	O
radiating	O
elements	O
through	O
devices	O
called	O
phase	B-Algorithm
shifters	I-Algorithm
,	O
controlled	O
by	O
a	O
computer	O
system	O
,	O
which	O
can	O
alter	O
the	O
phase	O
or	O
signal	O
delay	O
electronically	O
,	O
thus	O
steering	O
the	O
beam	O
of	O
radio	O
waves	O
to	O
a	O
different	O
direction	O
.	O
</s>
<s>
Since	O
the	O
size	O
of	O
an	O
antenna	B-Algorithm
array	I-Algorithm
must	O
extend	O
many	O
wavelengths	O
to	O
achieve	O
the	O
high	O
gain	O
needed	O
for	O
narrow	O
beamwidth	O
,	O
phased	O
arrays	O
are	O
mainly	O
practical	O
at	O
the	O
high	O
frequency	O
end	O
of	O
the	O
radio	O
spectrum	O
,	O
in	O
the	O
UHF	O
and	O
microwave	O
bands	O
,	O
in	O
which	O
the	O
operating	O
wavelengths	O
are	O
conveniently	O
small	O
.	O
</s>
<s>
Phased	O
arrays	O
were	O
originally	O
conceived	O
for	O
use	O
in	O
military	O
radar	B-Application
systems	I-Application
,	O
to	O
steer	O
a	O
beam	O
of	O
radio	O
waves	O
quickly	O
across	O
the	O
sky	O
to	O
detect	O
planes	O
and	O
missiles	O
.	O
</s>
<s>
The	O
phased	O
array	O
principle	O
is	O
also	O
used	O
in	O
acoustics	O
,	O
and	O
phased	O
arrays	O
of	O
acoustic	B-Algorithm
transducers	I-Algorithm
are	O
used	O
in	O
medical	B-Application
ultrasound	I-Application
imaging	O
scanners	O
(	O
phased	O
array	O
ultrasonics	O
)	O
,	O
oil	O
and	O
gas	O
prospecting	O
(	O
reflection	O
seismology	O
)	O
,	O
and	O
military	O
sonar	B-Application
systems	O
.	O
</s>
<s>
The	O
term	O
"	O
phased	O
array	O
"	O
is	O
also	O
used	O
to	O
a	O
lesser	O
extent	O
for	O
unsteered	O
array	B-Algorithm
antennas	I-Algorithm
in	O
which	O
the	O
phase	O
of	O
the	O
feed	O
power	O
and	O
thus	O
the	O
radiation	B-Device
pattern	I-Device
of	O
the	O
antenna	B-Algorithm
array	I-Algorithm
is	O
fixed	O
.	O
</s>
<s>
For	O
example	O
,	O
AM	O
broadcast	O
radio	O
antennas	O
consisting	O
of	O
multiple	O
mast	O
radiators	O
fed	O
so	O
as	O
to	O
create	O
a	O
specific	O
radiation	B-Device
pattern	I-Device
are	O
also	O
called	O
"	O
phased	O
arrays	O
"	O
.	O
</s>
<s>
However	O
,	O
the	O
four	O
most	O
common	O
are	O
the	O
passive	B-Algorithm
electronically	I-Algorithm
scanned	I-Algorithm
array	I-Algorithm
(	O
PESA	O
)	O
,	O
active	B-Architecture
electronically	I-Architecture
scanned	I-Architecture
array	I-Architecture
(	O
AESA	O
)	O
,	O
hybrid	O
beam	B-Algorithm
forming	I-Algorithm
phased	O
array	O
,	O
and	O
digital	B-Algorithm
beam	I-Algorithm
forming	I-Algorithm
(	O
DBF	O
)	O
array	O
.	O
</s>
<s>
A	O
passive	B-Algorithm
phased	I-Algorithm
array	I-Algorithm
or	O
passive	B-Algorithm
electronically	I-Algorithm
scanned	I-Algorithm
array	I-Algorithm
(	O
PESA	O
)	O
is	O
a	O
phased	O
array	O
in	O
which	O
the	O
antenna	O
elements	O
are	O
connected	O
to	O
a	O
single	O
transmitter	O
and/or	O
receiver	O
,	O
as	O
shown	O
in	O
the	O
first	O
animation	O
at	O
top	O
.	O
</s>
<s>
An	O
active	B-Architecture
phased	I-Architecture
array	I-Architecture
or	O
active	B-Architecture
electronically	I-Architecture
scanned	I-Architecture
array	I-Architecture
(	O
AESA	O
)	O
is	O
a	O
phased	O
array	O
in	O
which	O
each	O
antenna	O
element	O
has	O
an	O
analog	O
transmitter/receiver	O
(	O
T/R	O
)	O
module	O
which	O
creates	O
the	O
phase	O
shifting	O
required	O
to	O
electronically	O
steer	O
the	O
antenna	O
beam	O
.	O
</s>
<s>
A	O
hybrid	O
beam	B-Algorithm
forming	I-Algorithm
phased	O
array	O
can	O
be	O
thought	O
of	O
as	O
a	O
combination	O
of	O
an	O
AESA	O
and	O
a	O
digital	B-Algorithm
beam	I-Algorithm
forming	I-Algorithm
phased	O
array	O
.	O
</s>
<s>
It	O
uses	O
subarrays	O
that	O
are	O
active	B-Architecture
phased	I-Architecture
arrays	I-Architecture
(	O
for	O
instance	O
,	O
a	O
subarray	O
may	O
be	O
64	O
,	O
128	O
or	O
256	O
elements	O
and	O
the	O
number	O
of	O
elements	O
depends	O
upon	O
system	O
requirements	O
)	O
.	O
</s>
<s>
A	O
digital	B-Algorithm
beam	I-Algorithm
forming	I-Algorithm
(	O
DBF	O
)	O
phased	O
array	O
has	O
a	O
digital	O
receiver/exciter	O
at	O
each	O
element	O
in	O
the	O
array	O
.	O
</s>
<s>
The	O
phase	B-Algorithm
shifters	I-Algorithm
compensate	O
for	O
the	O
different	O
path	O
lengths	O
of	O
the	O
waves	O
due	O
to	O
the	O
antenna	O
elements	O
 '	O
varying	O
position	O
on	O
the	O
surface	O
,	O
allowing	O
the	O
array	O
to	O
radiate	O
a	O
plane	O
wave	O
.	O
</s>
<s>
During	O
World	O
War	O
II	O
,	O
Nobel	O
laureate	O
Luis	O
Alvarez	O
used	O
phased	O
array	O
transmission	O
in	O
a	O
rapidly	O
steerable	O
radar	B-Application
system	I-Application
for	O
"	O
ground-controlled	O
approach	O
"	O
,	O
a	O
system	O
to	O
aid	O
in	O
the	O
landing	O
of	O
aircraft	O
.	O
</s>
<s>
This	O
design	O
is	O
also	O
used	O
for	O
radar	B-Application
,	O
and	O
is	O
generalized	O
in	O
interferometric	O
radio	O
antennas	O
.	O
</s>
<s>
In	O
2007	O
,	O
DARPA	O
researchers	O
announced	O
a	O
16	O
element	O
phased	B-Algorithm
array	I-Algorithm
radar	I-Algorithm
antenna	O
which	O
was	O
also	O
integrated	O
with	O
all	O
the	O
necessary	O
circuits	O
on	O
a	O
single	O
silicon	O
chip	O
and	O
operated	O
at	O
30	O
–	O
50GHz	O
.	O
</s>
<s>
The	O
relative	O
amplitudes	B-Application
of	O
—	O
and	O
constructive	O
and	O
destructive	O
interference	O
effects	O
among	O
—	O
the	O
signals	O
radiated	O
by	O
the	O
individual	O
antennas	O
determine	O
the	O
effective	O
radiation	B-Device
pattern	I-Device
of	O
the	O
array	O
.	O
</s>
<s>
A	O
phased	O
array	O
may	O
be	O
used	O
to	O
point	O
a	O
fixed	O
radiation	B-Device
pattern	I-Device
,	O
or	O
to	O
scan	O
rapidly	O
in	O
azimuth	O
or	O
elevation	O
.	O
</s>
<s>
Simultaneous	O
electrical	O
scanning	O
in	O
both	O
azimuth	O
and	O
elevation	O
was	O
first	O
demonstrated	O
in	O
a	O
phased	O
array	B-Algorithm
antenna	I-Algorithm
at	O
Hughes	O
Aircraft	O
Company	O
,	O
California	O
in	O
1957	O
.	O
</s>
<s>
In	O
broadcast	O
engineering	O
,	O
the	O
term	O
'	O
phased	O
array	O
 '	O
has	O
a	O
meaning	O
different	O
from	O
its	O
normal	O
meaning	O
,	O
it	O
means	O
an	O
ordinary	O
array	B-Algorithm
antenna	I-Algorithm
,	O
an	O
array	O
of	O
multiple	O
mast	O
radiators	O
designed	O
to	O
radiate	O
a	O
directional	O
radiation	B-Device
pattern	I-Device
,	O
as	O
opposed	O
to	O
a	O
single	O
mast	O
which	O
radiates	O
an	O
omnidirectional	O
pattern	O
.	O
</s>
<s>
Broadcast	O
phased	O
arrays	O
have	O
fixed	O
radiation	B-Device
patterns	I-Device
and	O
are	O
not	O
'	O
steered	O
 '	O
during	O
operation	O
as	O
are	O
other	O
phased	O
arrays	O
.	O
</s>
<s>
Due	O
to	O
the	O
differences	O
between	O
daytime	O
and	O
nighttime	O
ionospheric	O
propagation	O
at	O
mediumwave	B-Algorithm
frequencies	O
,	O
it	O
is	O
common	O
for	O
AM	O
broadcast	O
stations	O
to	O
change	O
between	O
day	O
(	O
groundwave	O
)	O
and	O
night	O
(	O
skywave	O
)	O
radiation	B-Device
patterns	I-Device
by	O
switching	O
the	O
phase	O
and	O
power	O
levels	O
supplied	O
to	O
the	O
individual	O
antenna	O
elements	O
(	O
mast	O
radiators	O
)	O
daily	O
at	O
sunrise	B-Application
and	O
sunset	B-Application
.	O
</s>
<s>
Phased	O
arrays	O
were	O
invented	O
for	O
radar	B-Application
tracking	O
of	O
ballistic	O
missiles	O
,	O
and	O
because	O
of	O
their	O
fast	O
tracking	O
abilities	O
phased	B-Algorithm
array	I-Algorithm
radars	I-Algorithm
are	O
widely	O
used	O
in	O
military	O
applications	O
.	O
</s>
<s>
For	O
example	O
,	O
because	O
of	O
the	O
rapidity	O
with	O
which	O
the	O
beam	O
can	O
be	O
steered	O
,	O
phased	B-Algorithm
array	I-Algorithm
radars	I-Algorithm
allow	O
a	O
warship	O
to	O
use	O
one	O
radar	B-Application
system	I-Application
for	O
surface	O
detection	O
and	O
tracking	O
(	O
finding	O
ships	O
)	O
,	O
air	O
detection	O
and	O
tracking	O
(	O
finding	O
aircraft	O
and	O
missiles	O
)	O
and	O
missile	O
uplink	O
capabilities	O
.	O
</s>
<s>
Before	O
using	O
these	O
systems	O
,	O
each	O
surface-to-air	O
missile	O
in	O
flight	O
required	O
a	O
dedicated	O
fire-control	B-Application
radar	B-Application
,	O
which	O
meant	O
that	O
radar-guided	O
weapons	O
could	O
only	O
engage	O
a	O
small	O
number	O
of	O
simultaneous	O
targets	O
.	O
</s>
<s>
Because	O
the	O
antenna	B-Device
pattern	I-Device
is	O
electronically	O
steered	O
,	O
phased	O
array	O
systems	O
can	O
direct	O
radar	B-Application
beams	O
fast	O
enough	O
to	O
maintain	O
a	O
fire	B-Application
control	I-Application
quality	I-Application
track	O
on	O
many	O
targets	O
simultaneously	O
while	O
also	O
controlling	O
several	O
in-flight	O
missiles	O
.	O
</s>
<s>
The	O
AN/SPY	O
-1	O
phased	B-Algorithm
array	I-Algorithm
radar	I-Algorithm
,	O
part	O
of	O
the	O
Aegis	B-Application
Combat	I-Application
System	I-Application
deployed	O
on	O
modern	O
U.S.	O
cruisers	O
and	O
destroyers	B-Application
,	O
"	O
is	O
able	O
to	O
perform	O
search	O
,	O
track	O
and	O
missile	O
guidance	O
functions	O
simultaneously	O
with	O
a	O
capability	O
of	O
over	O
100	O
targets.	O
"	O
</s>
<s>
Likewise	O
,	O
the	O
Thales	O
Herakles	O
phased	O
array	O
multi-function	O
radar	B-Application
used	O
in	O
service	O
with	O
France	O
and	O
Singapore	O
has	O
a	O
track	O
capacity	O
of	O
200	O
targets	O
and	O
is	O
able	O
to	O
achieve	O
automatic	O
target	O
detection	O
,	O
confirmation	O
and	O
track	O
initiation	O
in	O
a	O
single	O
scan	O
,	O
while	O
simultaneously	O
providing	O
mid-course	O
guidance	O
updates	O
to	O
the	O
MBDA	O
Aster	O
missiles	O
launched	O
from	O
the	O
ship	O
.	O
</s>
<s>
The	O
German	O
Navy	O
and	O
the	O
Royal	O
Dutch	O
Navy	O
have	O
developed	O
the	O
Active	B-Architecture
Phased	I-Architecture
Array	I-Architecture
Radar	B-Application
System	I-Application
(	O
APAR	O
)	O
.	O
</s>
<s>
The	O
MIM-104	O
Patriot	O
and	O
other	O
ground-based	O
antiaircraft	O
systems	O
use	O
phased	B-Algorithm
array	I-Algorithm
radar	I-Algorithm
for	O
similar	O
benefits	O
.	O
</s>
<s>
Phased	O
arrays	O
are	O
used	O
in	O
naval	O
sonar	B-Application
,	O
in	O
active	O
(	O
transmit	O
and	O
receive	O
)	O
and	O
passive	O
(	O
receive	O
only	O
)	O
and	O
hull-mounted	O
and	O
towed	O
array	O
sonar	B-Application
.	O
</s>
<s>
The	O
MESSENGER	B-Protocol
spacecraft	O
was	O
a	O
space	O
probe	O
mission	O
to	O
the	O
planet	O
Mercury	O
(	O
2011	O
–	O
2015	O
)	O
.	O
</s>
<s>
The	O
antenna	O
,	O
which	O
uses	O
the	O
X	B-Algorithm
band	I-Algorithm
,	O
used	O
26	O
radiative	O
elements	O
and	O
can	O
gracefully	B-General_Concept
degrade	I-General_Concept
.	O
</s>
<s>
The	O
National	O
Severe	O
Storms	O
Laboratory	O
has	O
been	O
using	O
a	O
SPY-1A	O
phased	O
array	B-Algorithm
antenna	I-Algorithm
,	O
provided	O
by	O
the	O
US	O
Navy	O
,	O
for	O
weather	O
research	O
at	O
its	O
Norman	O
,	O
Oklahoma	O
facility	O
since	O
April	O
23	O
,	O
2003	O
.	O
</s>
<s>
Current	O
project	O
participants	O
include	O
the	O
National	O
Severe	O
Storms	O
Laboratory	O
and	O
National	O
Weather	O
Service	O
Radar	B-Application
Operations	O
Center	O
,	O
Lockheed	O
Martin	O
,	O
United	O
States	O
Navy	O
,	O
University	O
of	O
Oklahoma	O
School	O
of	O
Meteorology	O
,	O
School	O
of	O
Electrical	O
and	O
Computer	O
Engineering	O
,	O
and	O
Atmospheric	O
Radar	B-Application
Research	O
Center	O
,	O
Oklahoma	O
State	O
Regents	O
for	O
Higher	O
Education	O
,	O
the	O
Federal	O
Aviation	O
Administration	O
,	O
and	O
Basic	O
Commerce	O
and	O
Industries	O
.	O
</s>
<s>
A	O
team	O
from	O
Japan	O
's	O
RIKEN	O
Advanced	O
Institute	O
for	O
Computational	O
Science	O
(	O
AICS	O
)	O
has	O
begun	O
experimental	O
work	O
on	O
using	O
phased-array	O
radar	B-Application
with	O
a	O
new	O
algorithm	O
for	O
instant	O
weather	O
forecasts	O
.	O
</s>
<s>
Synthetic	O
array	O
heterodyne	O
detection	O
is	O
an	O
efficient	O
method	O
for	O
multiplexing	B-Architecture
an	O
entire	O
phased	O
array	O
onto	O
a	O
single	O
element	O
photodetector	O
.	O
</s>
<s>
The	O
dynamic	O
beam	B-Algorithm
forming	I-Algorithm
in	O
an	O
optical	O
phased	O
array	O
transmitter	O
can	O
be	O
used	O
to	O
electronically	O
raster	O
or	O
vector	O
scan	O
images	O
without	O
using	O
lenses	O
or	O
mechanically	O
moving	O
parts	O
in	O
a	O
lensless	O
projector	O
.	O
</s>
<s>
It	O
is	O
designed	O
to	O
provide	O
broadband	O
internet	O
connectivity	O
to	O
consumers	O
;	O
the	O
user	O
terminals	O
of	O
the	O
system	O
will	O
use	O
phased	O
array	B-Algorithm
antennas	I-Algorithm
.	O
</s>
<s>
By	O
2014	O
,	O
phased	O
array	B-Algorithm
antennas	I-Algorithm
were	O
integrated	O
into	O
RFID	B-Application
systems	O
to	O
increase	O
the	O
area	O
of	O
coverage	O
of	O
a	O
single	O
system	O
by	O
100%	O
to	O
while	O
still	O
using	O
traditional	O
passive	O
UHF	O
tags	O
.	O
</s>
<s>
A	O
phased	O
array	O
of	O
acoustic	B-Algorithm
transducers	I-Algorithm
,	O
denominated	O
airborne	O
ultrasound	O
tactile	O
display	O
(	O
AUTD	O
)	O
,	O
was	O
developed	O
in	O
2008	O
at	O
the	O
University	O
of	O
Tokyo	O
's	O
Shinoda	O
Lab	O
to	O
induce	O
tactile	O
feedback	O
.	O
</s>
<s>
There	O
are	O
two	O
main	O
types	O
of	O
beamformers	B-Algorithm
.	O
</s>
<s>
These	O
are	O
time	O
domain	O
beamformers	B-Algorithm
and	O
frequency	O
domain	O
beamformers	B-Algorithm
.	O
</s>
<s>
Time	O
domain	O
beamformer	B-Algorithm
works	O
by	O
introducing	O
time	O
delays	O
.	O
</s>
<s>
A	O
Butler	B-Algorithm
matrix	I-Algorithm
allows	O
several	O
beams	O
to	O
be	O
formed	O
simultaneously	O
,	O
or	O
one	O
beam	O
to	O
be	O
scanned	O
through	O
an	O
arc	O
.	O
</s>
<s>
Active	B-Architecture
phased	I-Architecture
array	I-Architecture
designs	O
use	O
individual	O
delay	O
lines	O
that	O
are	O
switched	O
on	O
and	O
off	O
.	O
</s>
<s>
Yttrium	O
iron	O
garnet	O
phase	B-Algorithm
shifters	I-Algorithm
vary	O
the	O
phase	O
delay	O
using	O
the	O
strength	O
of	O
a	O
magnetic	O
field	O
.	O
</s>
<s>
There	O
are	O
two	O
different	O
types	O
of	O
frequency	O
domain	O
beamformers	B-Algorithm
.	O
</s>
<s>
The	O
first	O
type	O
separates	O
the	O
different	O
frequency	O
components	O
that	O
are	O
present	O
in	O
the	O
received	O
signal	O
into	O
multiple	O
frequency	O
bins	O
(	O
using	O
either	O
a	O
Discrete	B-Algorithm
Fourier	I-Algorithm
transform	I-Algorithm
(	O
DFT	O
)	O
or	O
a	O
filterbank	O
)	O
.	O
</s>
<s>
When	O
different	O
delay	O
and	O
sum	O
beamformers	B-Algorithm
are	O
applied	O
to	O
each	O
frequency	O
bin	O
,	O
the	O
result	O
is	O
that	O
the	O
main	O
lobe	O
simultaneously	O
points	O
in	O
multiple	O
different	O
directions	O
at	O
each	O
of	O
the	O
different	O
frequencies	O
.	O
</s>
<s>
This	O
can	O
be	O
an	O
advantage	O
for	O
communication	O
links	O
,	O
and	O
is	O
used	O
with	O
the	O
SPS-48	O
radar	B-Application
.	O
</s>
<s>
The	O
other	O
type	O
of	O
frequency	O
domain	O
beamformer	B-Algorithm
makes	O
use	O
of	O
Spatial	O
Frequency	O
.	O
</s>
<s>
Each	O
array	O
element	O
incorporates	O
an	O
adjustable	O
phase	B-Algorithm
shifter	I-Algorithm
that	O
are	O
collectively	O
used	O
to	O
move	O
the	O
beam	O
with	O
respect	O
to	O
the	O
array	O
face	O
.	O
</s>
<s>
This	O
can	O
produce	O
antenna	O
motion	O
fast	O
enough	O
to	O
use	O
a	O
small	O
pencil-beam	O
to	O
simultaneously	O
track	O
multiple	O
targets	O
while	O
searching	O
for	O
new	O
targets	O
using	O
just	O
one	O
radar	B-Application
set	O
(	O
track	O
while	O
search	O
)	O
.	O
</s>
<s>
The	O
position	O
of	O
mechanically	O
steered	O
antennas	O
can	O
be	O
predicted	O
,	O
which	O
can	O
be	O
used	O
to	O
create	O
electronic	O
countermeasures	O
that	O
interfere	O
with	O
radar	B-Application
operation	O
.	O
</s>
<s>
Fixed	O
phased	O
array	B-Algorithm
antennas	I-Algorithm
are	O
typically	O
used	O
to	O
create	O
an	O
antenna	O
with	O
a	O
more	O
desirable	O
form	O
factor	O
than	O
the	O
conventional	O
parabolic	O
reflector	O
or	O
cassegrain	O
reflector	O
.	O
</s>
<s>
Fixed	O
phased	O
arrays	O
incorporate	O
fixed	O
phase	B-Algorithm
shifters	I-Algorithm
.	O
</s>
<s>
For	O
example	O
,	O
most	O
commercial	O
FM	O
Radio	O
and	O
TV	O
antenna	O
towers	O
use	O
a	O
collinear	O
antenna	B-Algorithm
array	I-Algorithm
,	O
which	O
is	O
a	O
fixed	O
phased	O
array	O
of	O
dipole	O
elements	O
.	O
</s>
<s>
In	O
radar	B-Application
applications	O
,	O
this	O
kind	O
of	O
phased	O
array	O
is	O
physically	O
moved	O
during	O
the	O
track	O
and	O
scan	O
process	O
.	O
</s>
<s>
The	O
SPS-48	O
radar	B-Application
uses	O
multiple	O
transmit	O
frequencies	O
with	O
a	O
serpentine	O
delay	O
line	O
along	O
the	O
left	O
side	O
of	O
the	O
array	O
to	O
produce	O
vertical	O
fan	O
of	O
stacked	O
beams	O
.	O
</s>
<s>
Semi-active	O
radar	B-Application
homing	O
uses	O
monopulse	B-Algorithm
radar	I-Algorithm
that	O
relies	O
on	O
a	O
fixed	O
phased	O
array	O
to	O
produce	O
multiple	O
adjacent	O
beams	O
that	O
measure	O
angle	O
errors	O
.	O
</s>
<s>
The	O
phase	B-Algorithm
shifter	I-Algorithm
setting	O
is	O
the	O
same	O
for	O
transmit	O
and	O
receive	O
.	O
</s>
<s>
Active	B-Architecture
phased	I-Architecture
arrays	I-Architecture
do	O
not	O
require	O
phase	O
reset	O
after	O
the	O
end	O
of	O
the	O
transmit	O
pulse	O
,	O
which	O
is	O
compatible	O
with	O
Doppler	B-Algorithm
radar	I-Algorithm
and	O
pulse-Doppler	B-Algorithm
radar	I-Algorithm
.	O
</s>
<s>
Passive	B-Algorithm
phased	I-Algorithm
arrays	I-Algorithm
typically	O
use	O
large	O
amplifiers	O
that	O
produce	O
all	O
of	O
the	O
microwave	O
transmit	O
signal	O
for	O
the	O
antenna	O
.	O
</s>
<s>
Phase	B-Algorithm
shifters	I-Algorithm
typically	O
consist	O
of	O
waveguide	O
elements	O
controlled	O
by	O
magnetic	O
field	O
,	O
voltage	O
gradient	O
,	O
or	O
equivalent	O
technology	O
.	O
</s>
<s>
The	O
phase	O
shift	O
process	O
used	O
with	O
passive	B-Algorithm
phased	I-Algorithm
arrays	I-Algorithm
typically	O
puts	O
the	O
receive	O
beam	O
and	O
transmit	O
beam	O
into	O
diagonally	O
opposite	O
quadrants	O
.	O
</s>
<s>
That	O
requires	O
a	O
phase	O
impulse	O
that	O
degrades	O
sub-clutter	O
visibility	O
performance	O
on	O
Doppler	B-Algorithm
radar	I-Algorithm
and	O
Pulse-Doppler	B-Algorithm
radar	I-Algorithm
.	O
</s>
<s>
As	O
an	O
example	O
,	O
Yttrium	O
iron	O
garnet	O
phase	B-Algorithm
shifters	I-Algorithm
must	O
be	O
changed	O
after	O
transmit	O
pulse	O
quench	O
and	O
before	O
receiver	O
processing	O
starts	O
to	O
align	O
transmit	O
and	O
receive	O
beams	O
.	O
</s>
<s>
Passive	B-Algorithm
phased	I-Algorithm
array	I-Algorithm
design	O
is	O
used	O
in	O
the	O
AEGIS	B-Application
Combat	I-Application
System	I-Application
.	O
</s>
<s>
for	O
direction-of-arrival	B-Algorithm
estimation	O
.	O
</s>
