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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
MIT Lincoln LaboratoryRadar CourseJSH -3
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 Lincoln LaboratoryRadar CourseJSH -4
• 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
MIT Lincoln LaboratoryRadar CourseJSH -5
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
MIT Lincoln LaboratoryRadar CourseJSH -6
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
MIT Lincoln LaboratoryRadar CourseJSH -7
Outline
• History and Evolution of Phased Arrays• Phased Array Radar Fundamentals
– Array Beamforming– Electronic Scanning– Active Transmit-Receive Modules
• Summary
MIT Lincoln LaboratoryRadar CourseJSH -8
• 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
MIT Lincoln LaboratoryRadar CourseJSH -9
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
MIT Lincoln LaboratoryRadar CourseJSH -10
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
MIT Lincoln LaboratoryRadar CourseJSH -11
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
MIT Lincoln LaboratoryRadar CourseJSH -12
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
MIT Lincoln LaboratoryRadar CourseJSH -13
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
MIT Lincoln LaboratoryRadar CourseJSH -14
Active Array T/R Module
MIT Lincoln LaboratoryRadar CourseJSH -15
T/R Module / Subarray Integration
• High levels of integration reduce unit cost• Automated assembly and test reduces touch labor cost
64 Element Tile
MIT Lincoln LaboratoryRadar CourseJSH -16
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
MIT Lincoln LaboratoryRadar CourseJSH -17
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.