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Radar CourseJSH -1
MIT Lincoln Laboratory
Phased Array Radar Basics
Jeffrey Herd
MIT Lincoln Laboratory17 November 2009

MIT Lincoln LaboratoryRadar CourseJSH -2
Outline
History and Evolution of Phased Arrays Phased Array Radar Fundamentals
Array Beamforming Electronic Scanning Active Transmit-Receive Modules
Summary

T R
Radar Antenna Architectures
Dish Antenna
Very low cost Frequency diversity Slow scan rate High distribution loss Single point of failure
MILLSTONE
T R
Passive Phased Array
Beam agility Effective radar resource
management High distribution loss Higher cost
SPY-1
Beamformer
T R
Active Phased Array
Highest performance Effective radar resource
management Low distribution loss Highest cost
THAAD
T/R Modules

MIT LL Millstone Radar 2 Klystrons with 3 MW peak power
120 kW avg power
Center Frequency of 1295 MHz
8 MHz bandwidth
Millstone Klystron Tube
Dish Radar Example
Advantages High output power Low cost per watt
Disadvantages Single point of failure Large size
$400,000/tube 7 ft x 1ft 600 lbs 3% duty cycle 42 dB gain

Solid State Array Radar Example
PAVE PAWS First all-solid-state array radar UHF Band 1800 active transceiver T/R
modules, 340 W of peak power each
Advantages Electronic beam agility Low maintenance (no moving
parts) Graceful degradation
Disadvantages Higher cost per watt
Transmit and Receive Modules

Airb
orne
Surf
ace
Phased Array Radar Evolution
PatriotC-Band
SPY-1S-Band
B-1BX-Band
JSTARSX-Band
Passive Arrays( Phase Shifter at Element)
F/A-22X-Band
JSFX-Band
THAADX-Band
SBXX-Band
MP-RTIPX-Band
SPY-3X-Band
Active Arrays(Amplifiers + Phase Shifter at Element)
1985
1975
1980
2015
2005
2000
1995
1990
2010
Increasing Beam Agility

Outline
History and Evolution of Phased Arrays Phased Array Radar Fundamentals
Array Beamforming Electronic Scanning Active Transmit-Receive Modules
Summary

Multiple antennas combined to enhance radiation and shape pattern
Array Beamforming
Array Phased ArrayIsotropicElement
PhaseShifter
S
CombinerS S
Direction
Res
pons
e
Direction
Res
pons
e
Direction
Res
pons
e
Direction
Res
pons
e
Array

Array Beamforming (Beam Collimation)
Broadside Beam Scan To 30 deg
Want fields to interfere constructively (add) in desired directions, and interfere destructively (cancel) in the remaining space

Broadside Uniform Linear Array
d = l/4 separation d = l/2 separation d = l separation
Angle off Array q (deg) Angle off Array q (deg) Angle off Array q (deg)0 30 60 90 120 150 180
Dire
ctiv
ity (d
Bi)
GratingLobes
0 30 60 90 120 150 180-30
-20
-10
0
10
20
0 30 60 90 120 150 180
10 dBi7 dBi
10 dBi
L = (N-1) d
z
90q = Maximum at
90cos 0k d
qy q b
= = + =
Design Goal0b =
Required Phase
N = 10 Elements
Limit element separation to d < l to preventgrating lobes for broadside array

Increasing Broadside Linear ArraySize by Adding Elements
Gain ~ 2N(d / l) ~ 2L / lfor long broadside array without grating lobes*
N = 10 Elements
Dire
ctiv
ity (d
Bi)
Angle off Array q (deg)0 30 60 90 120 150 1800 30 60 90 120 150 1800 30 60 90 120 150 180-30
-20
-10
0
10
20
10 dBi 13 dBi 16 dBi
Angle off Array q (deg) Angle off Array q (deg)
N = 40 ElementsN = 20 Elements
Element Separation d = l/2
* d < l
L = (N-1) d
z

Excitation AmplitudesTapers Across 10 Element Linear Array
Uniform Amplitude Binomial26 dB Dolph-Tschebyscheff
-
1 2 3 4 5 6 7 8 9 10
1
2
3
1 2 3 4 5 6 7 8 9 10
1
2
3
1 2 3 4 5 6 7 8 9 10
50
100
150
1
0 30 60 90 120 150 180-40
-35
-30
-25
-20
-15
-10
-5
0
0 30 60 90 120 150 180-40
-35
-30
-25
-20
-15
-10
-5
0
0 30 60 90 120 150 180-40
-35
-30
-25
-20
-15
-10
-5
0
13 dB SLL
26 dB SLL
No Sidelobes -Theoretical Result!
Amplitude & Phase Errors Limit the Sidelobe Level (SLL)That Can Be Achieved in Practice: > 40 dB is Challenging

Polarization
rE
HorizontalLinear
(with respectto Earth)
Defined by behavior of the electric field vector as it propagates in time
r
E
VerticalLinear
(with respectto Earth)
ElectromagneticWave Electric Field
Magnetic Field
q
f
r

Active Array T/R Module

T/R Module / Subarray Integration
High levels of integration reduce unit cost Automated assembly and test reduces touch labor cost
64 Element Tile

Summary
Phased array provides improvements in radar functionality and performance
Beam agility
Effective radar resource management
Graceful degradation with module failures
Current trend is towards active arrays with distributed T/R modules
Large number of distributed active components and control
High levels of integration required to achieve low cost

References
General Antenna Theory and Design: Balanis, C.A., Antenna Theory: Analysis and Design, 2nd ed. New
York: Wiley, 1997.* Elliot, R. S., Antenna Theory and Design. New Jersey: Prentice-Hall,
1981. Kraus, J.D., Antennas 2nd ed. New York: McGraw-Hill, 1993. Stutzman W. L., Thiele, G. A., Antenna Theory and Design, 2nd ed.
New York: Wiley, 1998. Special Topics:
Hansen, R. C., Microwave Scanning Antennas. California: Peninsula Publishing, 1985.
Pozar, D. M., Schaubert, D. H. eds., Microstrip Antennas: The Analysis and Design of Microstrip Antennas and Arrays. New York: IEEE, 1995.
Handbooks: Lo, Y.T. and Lee S.W. eds., Antenna Handbook, Theory, Applications,
and Design. New York: Van Nostrand Reinhold, 1993. Mailloux, R. J., Phased Array Antenna Handbook. Artech House,
1994.
Phased Array Radar BasicsOutlineRadar Antenna ArchitecturesSlide Number 4Solid State Array Radar Example Slide Number 6OutlineArray BeamformingArray Beamforming (Beam Collimation)Slide Number 10Slide Number 11Excitation AmplitudesTapers Across 10 Element Linear ArrayPolarizationActive Array T/R ModuleT/R Module / Subarray IntegrationSummaryReferences

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