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Phased Array Antenna
Myung Jin Shin
May 22, 2015
High-Speed Circuits & Systems Lab Department of Electrical and Electronic Engineering
Yonsei University
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Content
History of phased array
Introduction
Basic concept of phased array antenna
Benefit of phased array
Time Delay Unit
Application for phased array antenna
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History
Early radar (Mid-1940)
– Military radar
– Army’s “bed spring” array: first radar signals bounced off the moon
Year of 1950s
– Start to use electronic phasing of individual array steer radar beam
– Many ways to steer radar but couldn’t realize
Present
– Electronic beam movement is achievable
– Price problem
– Modern solid state phased array will be a solution
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Phase array is directive antenna made with individual radiating source
(several units to thousands of elements)
Radiating elements: dipoles, open-ended waveguides, slotted
waveguides, microstrip antennas, helices, spirals
The shape and direction of pattern is determined by relative phases
amplitudes applied to each radiating element
Introduction
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Radiation Patterns by Different Phase
Two λ/2 dipoles
Spacing = λ/2
Four λ/2 dipoles
Spacing = λ/2
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Linear array: Elements arranged on a straight line in one dimension
Planar array: Elements arranged on a plane in two dimensions
– Rectangular, Square or circular aperture
Conformal array: elements are distributed on a non-planar surface
Different types of Phased Array
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Phase Relation between Elements
- u : unit direction vector in antenna coordinate system
- r : location of antenna element (=(x,y,z)T)
- Path length difference between element(r) with origin
Delays and direction cosines
| || | cos( )xu yv zw Tr u r u r,u
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Beamforming
Signal at element r
Beam into direction u0 with N antenna elements by compensating delays
f: transmit frequency, c: velocity of light,
H: conjugate transpose, a(u0): steering vector
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Beamforming
Linear antenna, elements separated by dλ/2
Uniform linear antenna: periodic main beam repeated (grating lobes)
Grating lobes can be avoid by irregular spacing
f(u)=a(0)Ha(u): antenna pattern
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E field on the plane wave
Antenna ith received signal (x=y=0)
Benefit of Antenna Array
2cos ij z
iX e
( )
| |(sin cos sin sin cos )
( , , ) x y zj k x k y k z
j x y z
j
E x y z e
e
e
k
kr
3-elemet antenna array
Summation of received signal
1 2 3
2 2 2cos cos cos
23 1coscos
1 1
i
j z j z j z
j zjm
i m
Y e e e
e e
Basic antenna model
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Benefit of Antenna Array
Antenna Array output magnitude
Vs arrival angle
- 90 degree: most receptive
- 45, 135 degree: zero output power
- Phased array can cancel out undesirable direction & receive most
sensitively from other directions.
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Planar phased array
9-element planar phased array Received signal by input angle
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Time Delay Unit (TDU)
Phase shifter do not provide TTD beam distort over frequency
TDU: structure that provide specific time delay using a multi-path structure
TTD improve bandwidth and used at subarray level
Problem
– Different length of transmission line loss ↑(length, frequency)
Solution
– Increase loss of short path by attenuator
– Increase loss at low frequency by gain equalizer
# TTD: True Time Delay
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Electrical Beam Shaping
<Defocusing> <Focusing>
Convex lens Concave lens
Concave wave fronts Convex wave fronts
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Application
Patriot missile radar
Patriot: phased array track to intercept of target
Phased array satellite antenna
High-Speed Circuits & Systems Lab Department of Electrical and Electronic Engineering
Yonsei University
Phased Array Antenna
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Reference
http://www.antenna-theory.com/arrays/main.php#phased
http://www.radartutorial.eu/06.antennas/Phased%20Array%20Antenna.en.html
http://tempest.das.ucdavis.edu/mmwave/paa.html
http://encyclopedia2.thefreedictionary.com/Phased+array+antenna
http://www.microwaves101.com/encyclopedias/phased-array-antennas
Alan J. Fenn,”The development of phased-array radar technology”, Volume 12,
number 2, 2000, Lincoln Laboratory Journal
