[Anastasis Polycarpou, Constantine Balanis] Introd(BookFi.org)
Electronic Scanned Array Design · 2016-09-27 · – First sidelobe at -17.8 dB – 3 dB beamwidth...
Transcript of Electronic Scanned Array Design · 2016-09-27 · – First sidelobe at -17.8 dB – 3 dB beamwidth...
Electronic Scanned Array DesignSCF01
John S. Williams
The Aerospace Corporation (retired)
Slide 1of 255
Course Objectivesj
• Provide a basic understanding of ESA design principles,history and applications
Presentation will focus on antenna hardware– Presentation will focus on antenna hardware– Radar antennas are the focus of this presentation
• Communications and receive antennas differ only in detailsy– ESA functionality enables or enhances radar modes but radar
modes will not be addressed in any detail
SCF01 Electronic Scanned Array DesignSlide 2of 255
Abstract
Design Principles and ApproachesG f f f SGeneral design principles of aperture antennas are applied to the specific case of ESA design. System applications set the framework for requirements allocation and flowdown.Antenna Architectures and Functional PartitioningThe advantages and disadvantages of ESA and reflector antennas as well as ESA feeds for reflectors are compared and contrasted. Common ESA design issues are described, including array partitioning and subarrays, lattice tradeoffs, feed design, causes and mitigation of sidelobes beam steering approaches and techniques for beam shaping Numerical examplessidelobes, beam steering approaches and techniques for beam shaping. Numerical examples using Matlab illustrate performance of specific designs.Practical Design ConsiderationsESA performance is constrained by the selection and limitations of specific componentsESA performance is constrained by the selection and limitations of specific components. Objectives of size, weight, power, thermal dissipation, performance and cost drive tradeoffs among radiating elements, T/R modules, monolithic microwave integrated circuits (MMICs), microwave distribution and packaging. Proposed and Operational ExamplesRecent radar satellite designs will be assessed to illustrate actual performance and design tradeoffs. Current L-band system proposals contrast different design approaches.y p p g pp
SCF01 Electronic Scanned Array DesignSlide 3of 255
Antennas
• One of the most important determinants of microwave system• One of the most important determinants of microwave system(radar, communications, other) performance
• Requirements are determined by system performance allocation andflow-downflow down
• Attributes include:– Beam width, shape and sidelobes
• Uniform illumination sidelobes -13 dB (rectangular aperture) or -17 dB (circularUniform illumination sidelobes 13 dB (rectangular aperture) or 17 dB (circularaperture) are too high for most purposes
– Instantaneous and tunable bandwidth– Size
• SAR (square) vs GMTI (rectangular) Aspect Ratios• SAR (square) vs GMTI (rectangular) Aspect Ratios• Deployment
– Thermal Dissipation– Weightg– Cost
• Thermal dissipation and power consumption will restrict system dutyfactor
SCF01 Electronic Scanned Array DesignSlide 4of 255
Electronically Scanned Array (ESA)y y ( )
• An ESA combines multiple elements with phase or time delays to form a beam in a specified direction
In contrast to a mechanically steered antenna physically rotates– In contrast to a mechanically steered antenna physically rotates an antenna to point a beam in a specified direction
• Phase or time delay is required to scan the beamy q• Gain control is required for beam shaping• ESA’s commonly include amplifiersESAs commonly include amplifiers
– overcome distribution and control loss– Replace transmitter power amplifier (TWTA)
SCF01 Electronic Scanned Array DesignSlide 5of 255
Reflector Antenna Radar Block Diagram
Exciter Transmitter
F mba
l
Control ProcessorFrequency & TimingReference D
uple
xer
Ant
ennaData request Gim
Radar data Signal Processor ReceiverReceiverProtection
Radar data Signal Processor Receiver
SCF01 Electronic Scanned Array Design
ESA incorporates functions shown in dashed box
Power SupplySlide 6of 255
Electronically Scanned Array Radar Block DiagramDiagram
ExciterTRM
TRMion
(s)
F
TRM
TRM
TRM
TRMDis
tribu
tiM
anifo
ld(
Control ProcessorFrequency & TimingReference
Data request Bea
TRM
TRM
TRM& L
ogic
fo
rmin
g M
Radar data Signal Processor Receiver(s)
am
TRM
TRM
TRMPow
er
Bea
mf
Radar data Signal Processor Receiver(s)TRM
SCF01 Electronic Scanned Array Design
ESA incorporates functions shown in dashed box
Power SupplySlide 7of 255
ESA Benefits
• Multiple beams• Instantaneous beam steering (agile beam)
– Reduces slew and settle time• Mainlobe shaping, sidelobe control and nulling for clutter and interference
mitigation• Multiple phase centers for MTI & multi-channel SAR
Enables angle of arrival measurement– Enables angle of arrival measurement– Additional degrees of freedom for clutter and interference mitigation
• Multiple concurrent radar modes.• Lower loss between amplifiers and free space• Inherent redundancy (multiple elements)
– Graceful degradation• Electronic Attack (EA) with very high Effective Radiated Power (ERP)• Stealth• Stealth
– Better match to free space – much less reflection/reradiation• Antenna surface deformation (deliberate or accidental) may be compensated• Space combining (low loss) of solid state power amplifiers
SCF01 Electronic Scanned Array DesignSlide 8of 255
ESA Performance Improvementp
• Multiple Azimuth Beam– Improved SAR resolution
M lti l El ti B22
24
26 -3 dB
• Multiple Elevation Beam– Improved stripmap area
rate18
20
22
(km
)
ate– SCORE (SCan On
Receive)14
16
18
Ran
ge ( ← Boresight
10
12Sensor altitude is 10.0 kmRange to horizon is 357.3 km
-10 -5 0 5 10
8
Cross Range (km)
Boresight range is 20.0 kmGrazing angle = 30.0°
SCF01 Electronic Scanned Array DesignSlide 9of 255
g ( )
Technology Environmentgy
• ESAs have recently become very prevalent for the sole reason that they have become much more affordable (they were always known to offer significant benefits but(they were always known to offer significant benefits but were unaffordable)
• T/R modules are a small fraction of radar system costT/R modules are a small fraction of radar system cost and a very small fraction of system cost
SCF01 Electronic Scanned Array DesignSlide 10
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Aperture Design
SCF01 Electronic Scanned Array DesignSlide 11
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Antenna Function
• Antenna objective is to create a current/voltage distribution which creates a specified beam pattern or v/vv/v.– Omni directional radio signals of little use (except for
broadcasting)
• Difficult to arrange in general– Arrays permit a sampled representation of current/voltage
i i l d i dpermitting almost any desired arrangement
• Two design approaches – analysis and synthesis
SCF01 Electronic Scanned Array DesignSlide 12
of 255
Basic Aperture Shapesp p
b
a
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bb
aa
bbb
aaa
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aaaa
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aaaaa
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• Square aperture • Round apertureq p– 4 by 8 wavelengths– First sidelobe is -13.2 dB– 3 dB beamwidth = ± 0.866 λ/D– first null at ± λ/D
Round aperture– 3 wavelengths radius– First sidelobe at -17.8 dB– 3 dB beamwidth = ± 1.03 λ/D– first null at ± 1.22 λ/D
From Balanis“Antenna Theory”Antenna Theory
Chapter 11
SCF01 Electronic Scanned Array DesignSlide 13
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Analysis Regions(exact to approximate)(exact to approximate)
Near FieldRegion
Fresnel orTransition
Region
Fraunhoferor Far Field
Region
nten
naA
n
D2 D2 D2 D2 2D20
NominalBeamwidth
For λ = 3cm and 16λ 4λ 2λ λ λ0
D = 1 meter 2m 8m 17m 33m 67m
For λ = 3cm and
SCF01 Electronic Scanned Array Design
D = 10 meter 208m833m 1,667m 3,333m 6,667m
Illustration from Lynch (© SciTech Publishing, Inc),Slide 14of 255
Regionsg
E t N Fi ld F Fi ldEvanescent Near Field Far FieldFresnel Fraunhofer
Near limit 0 3λ 2D²/λNear limit 0 3λ 2D /λFar limit 3λ 2D²/λ ∞Power decay R-n 1 R-1
E and H orthogonal
No Yes Yes
Z = 377 Ω No Yes YesZ0 = 377 Ω No Yes Yes
• Laser Pointer• Laser Pointer• = 630 nm, D = 1 mm => farfield at 3 meters
SCF01 Electronic Scanned Array DesignSlide 15
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Another Visualization
4λ
SCF01 Electronic Scanned Array Design 2D²/λ3λSlide 16
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General Conceptsp
Li it d iti• Linearity and superposition• Reciprocity (Lorenz)
– System behavior is independent of direction of energy transfer, ie antenna i h f i d ipattern is the same for transmit and receive
• Antenna pattern is the Fourier transform of aperture illumination– Discrete (sampled) vs continuous– The sample interval is the element spacing– λ/2 element spacing assures no grating lobes
(Nyquist-Shannon sampling theorem)R l ti li it (R l i h it i )– Resolution limit (Rayleigh criteria)
– Round vs square• Projected aperture (cosine θ dependence)
– Wheeler - Pozar• Polarization and principal planes• Radar Range Equationada a ge quat o
SCF01 Electronic Scanned Array DesignSlide 17
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Resolution
R t i di tl l t d t b d idth• Range measurement is directly related to bandwidth– Wide bandwidth waveform (eg chirp) required
• Angle measurement is directly related to antenna (aperture) Angle measurement is directly related to antenna (aperture) size– Can generate “synthetic” apertures larger than physical antenna
size by exploiting own platform motionsize by exploiting own platform motion• Angular resolution (Rayleigh criterion)
– Coherent or non-coherent– Deconvolution of PSF allows higher (super) resolution subject to
S/N– Consider two point sources (sinx/x) separated by small distance, fit
i ’/ ’ d t k diff l k t Pd/Pfsinx’/x’ and take difference, look at Pd/Pfa– Elements spaced closer than /2 potentially provide better
resolution
SCF01 Electronic Scanned Array DesignSlide 18
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Projected Aperturej p
• Projected aperture is the apparent angular extent of the aperture as viewed from a specified directionA t i i ti l t j t d t• Antenna gain is proportional to projected aperture
• Harold A. Wheeler derived this relationship in an early paperpaper
SCF01 Electronic Scanned Array DesignBroadside
θ=0 θ=30 θ=90θ=60 Slide 19of 255
Radar Range Equationg q
• Radar range determined by antenna size (area), transmit power, receive noise figure and bandwidth
SNR =PtG
262<
(4:)3kTeBFLR4
Pt = transmit powerG = antenna gainλ l th
(4:) kTeBFLR
λ = wavelengthσ = target cross sectionk = Boltzmann's constantT = system temperatureT system temperatureB = system bandwidthF = system noise figureL = system lossesR = range to target
SCF01 Electronic Scanned Array DesignSlide 20
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Friis Transmission Equationq
• Ratio of power received to power transmitted– Describes one-way radio links
Assumes antennas are aligned– Assumes antennas are aligned– Factor in parenthesis is free space loss
P3
642
Pr
Pt
= GtGr
36
4:R
42
Pr = received powerP = transmitted powerPt = transmitted powerGt = transmit antenna gainGr = receive antenna gainr g
SCF01 Electronic Scanned Array DesignSlide 21
of 255
Noise Equivalent Sigma Zeroq g
3
NESZ(<0) =
34:r
6
432Lsin3i
PGtGrc=pd
kBTB
2prop2sys
i th b k tt i ti
36
4PGtGrc=pd 2prop2sys
σ0 is the backscattering cross-sectionP = (peak) transmitted powerGt and Gr are the transmit and receive antenna gainsc speed of lightc = speed of light
PD = Pulse widthλ = Radar wavelengthr i Ranger i= RangekB = Boltzman constantB = Bandwidthθ = Incidence angleθi = Incidence angleη’s (<1) are the propagation and system losses.
SCF01 Electronic Scanned Array DesignSlide 22
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SAR Design Optimizationg p
• For a system limited by thermal noise, we can:• Reduce system losses and noise figure (hard to do)
D d t th (t k hit)• Decrease data swath (take coverage hit)• Increase transmit power• Increase pulse duration (may cause pulse timing issues)• Increase pulse duration (may cause pulse timing issues)• Decrease pulse bandwidth (for resolved targets)• Increase PRF (may cause range ambiguity problems)Increase PRF (may cause range ambiguity problems)• View target from more favorable angle• Increase antenna area (expensive, may lessen coverage)( p , y g )• Decrease slant range (may compromise mission
performance)
SCF01 Electronic Scanned Array DesignSlide 23
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ESA Design Approach
SCF01 Electronic Scanned Array DesignSlide 24
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Approachpp
A t l f id l t ill i ti• Arrays represent samples of ideal aperture illumination function– Sampling theorems apply– Undersampling ⇔ grating lobes– Oversampling associated with “super directivity”
• Arrays discussion assumes isotropic radiators• Arrays discussion assumes isotropic radiators– Array patterns are two-sided, element pattern is source of single-
sided patternEl t ff t ll d t ff t ll tt• Element effects generally do not affect overall pattern– Mutual coupling tends to narrow beams– Can create nulls (scan blindness) in unexpected directions( ) p
• Analysis• Synthesis
SCF01 Electronic Scanned Array DesignSlide 25
of 255
Discrete Representationp
• For a continuous illumination function f(x), the resulting beam pattern as a function of u (= sin θ) is
If l th ill i ti f ti t l i t l
F (u) =`
2
Z +1
!1
f(x) expjux dx
• If we sample the illumination function at equal intervals Δx where =(M-1)* Δx and f(m) = am, then`
M!1
A M d Δ 0 th b th i t l
F (u) =
M 1Xm=1
am expjkum"x
• As M ∞ and Δx 0 the sum becomes the integral.• In practice M > 10 is a fairly good approximation
SCF01 Electronic Scanned Array DesignSlide 26
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Array Conceptsy p
• Array factor and Element Pattern• Array partitioning and sub-arrays
– Phase shift– Time Delay– Digital domain– Digital domain
• Grating and quantization lobes– Sparse arraySparse array
• Amplitude and phase control for beam pointing and shaping, notably for sidelobe controlp g y
SCF01 Electronic Scanned Array DesignSlide 27
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Real and Synthetic Beam Formingy g
• Real beamforming uses samples collected at one point in time
Limited by number of elements/receivers– Limited by number of elements/receivers
• Synthetic beamforming uses samples collected over a time spantime span– Allows computation of multiple-beams, conceptually equal to
number of pixels in scene
SCF01 Electronic Scanned Array DesignSlide 28
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Arrays in Time (Synthetic)y ( y )
• Near field Scanner• Displaced Phase Center• SAR ⇔ array• Removes mutual coupling from consideration• Adds requirement for time coherence
SCF01 Electronic Scanned Array DesignSlide 29
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Antenna Conventions
f { ( )}• Radiated fields have an exp{j(ω·t-k·r)} dependence which is consistently omitted. It does not contribute to pattern calculations and is a constant factor in all calculations.calculations and is a constant factor in all calculations.– ω is angular frequency
• Equal to 2πf“ ” ( f )– k is “wavenumber” (spatial frequency)
• Equal to 2 π /λ
• Gain computed relative to an “isotropic” antenna whichGain computed relative to an isotropic antenna which radiates equally in all directions (4· π steradians).– This is one of the few antennas which is impossible (unrealizable)
d t th t t f th EMdue to the transverse nature of the EM wave• Directivity is pattern of lossless antenna
Gain is directivity times efficiency (1 – loss)Gain is directivity times efficiency (1 loss)
SCF01 Electronic Scanned Array DesignSlide 30
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Lattice Attributes
• Rectangular lattice and square aperture leads to a separable array pattern
Numerically equivalent to produce to two linear arrays at right– Numerically equivalent to produce to two linear arrays at right angles
• Triangular lattices slightly more complicatedg g y p
SCF01 Electronic Scanned Array DesignSlide 31
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Beam Pattern Analysis
SCF01 Electronic Scanned Array DesignSlide 32
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Generalized array (and coordinate system)system)
f• Plus Z direction is normal to the array face• Theta (θ) is measured relative to the +Z axis
Phi ( ) i d i th X Y l l ti t th X i• Phi (ϕ) is measured in the X-Y plane relative to the X axis• Array is represented by the lattice of circles in the X-Y plane
Plus ZPlus Z
30
180210240
30
270
150
120
60300
330
Plus Y906030
90Plus XSCF01 Electronic Scanned Array Design
Slide 33of 255
General Case
C id ll ti fZ
( )
• Consider a collection of radiating elements located at (xi, yi, zi) and an observer
(X Y Z )R0
YP (X, Y, Z) located at (x,y,z)
• Each radiating element is represented by a square(X1, Y1, Z1)
r
3
R0 represented by a square • The radiated field at the
observer’s location is the s m of the fields of each ofr1 `1
?
ri
X
sum of the fields of each of the radiating elements as seen at the same location
• This formulation used to analyze cases at end of presentationpresentation
SCF01 Electronic Scanned Array Design
After Mailloux Figure 1.5Slide 34
of 255
Element Contribution
• Each element i generates the field
Ei(r, 3, ?) = fi(3, ?) exp(!jkRi)/Ri
• Where
i( , , ?) i( , ?) p( j i)/
k = 2:/ 6
• Using the identity Ri = R ! r " ri
• We can rewrite the second term as
exp(!jkRi)
Ri
=exp(!jkR)
R! r " riexp(+jkri " r)
SCF01 Electronic Scanned Array DesignSlide 35
of 255
Fraunhofer Approximationpp
F di l d h i i• For distances large compared to the array size, ie R > r " ri
exp(!jkRi)
R=
exp(!jkR)
Rexp(+jkri " r)
• So that
Ri Rp(+j i )
Ei(r, 3, ?) =exp(!jkR)
Rfi(3,?) exp(+jkri " r)
• Adding a complex weight ai to each element, the resulting antenna pattern isp
E(r) =exp(!jkR)
R
Xi
aifi(3, ?) exp( jkri " r)
SCF01 Electronic Scanned Array Design
i
Slide 36of 255
Identical Elements
• It is customary to assume that each element has the same pattern so the element pattern may be taken out of the sumthe sum
E(r) = f(3, ?)exp(!jkR)
R
Xai exp( jkri " r)( ) ( , ?)
R
Xi
p( j )
• This formulation partitions the antenna pattern intoElement factor– Element factor
– Space factor– Array factory
SCF01 Electronic Scanned Array DesignSlide 37
of 255
Assumptionsp
Th f l ti i it l t th f ll i• The formulation is quite general except the following assumptions (which are more or less true)
• Far field assumption R > r " rip
– It is generally considered that is sufficient; this is termed the Fraunhofer region
R > r ri
R 6 2l2/6termed•the•Fraunhofer•region
Antenna•pattern•is•the•product•of•an•array•factor•and•an•element•factor
Th f t i ti l d t i d b th t i iti f– The•array•factor•is•entirely•determined•by•the•geometric•position•of•the•radiating•elements
– Identical•element•patterns•(which•is•violated•for•elements•near•the•d f th d t t l li ff t )edges•of•the•array•due•to•mutual•coupling•effects)
– The•element•factor•variation•mostly•affects•large•steering•angles•and•far•out•sidelobes
SCF01 Electronic Scanned Array DesignSlide 38
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Pattern Separabilityp y
A h h di i l d i l• Assume that the radiating elements are arranged in a rectangular grid in the X-Y plane such that
ri = r = m"x x + n"y y
m = 0,'1 ' 2 ' 3 . . . n = 0,'1' 2 ' 3 . . .
ri = rmn = m"xx + n"y y
r = xu + yv + z cos 3
• Then
r = xu + yv + z cos 3
u = sin 3 cos? v = sin 3 sin ?
• Then
ri " r = m"x u + n"y v
E(r) = f(3, ?)exp(!jkR)
R
Xamn exp ( jk (m"x u + n"y v))
SCF01 Electronic Scanned Array Design
i
Slide 39of 255
Pattern Decompositionp
• If we further assume that the complex element weight aimay be decomposed into x and y components
A d th t t l f t i th d t f t
amn = am an
• And the total array factor is the product of separate array factors in x and y
E(r) = f(3, ?)exp(!jkR)
R
Xam exp ( jk (m"x u))
Xan exp ( jk (n"y v))
Rm n
SCF01 Electronic Scanned Array DesignSlide 40
of 255
Pattern Multiplicationp
• The overall beam pattern is the product of the element pattern and the array patternA F t i Di t F i T f f A t• Array Factor is Discrete Fourier Transform of Aperture Weights (ai)– Sampling theorem– Sampling theorem– Element spacing
SCF01 Electronic Scanned Array DesignSlide 41
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16 Element Array = 4 x 4 Element Arrayy y
2016 element linear array0.5 λ element spacing
10 0° steering angle
(dB
)
-10
0
nna
Gai
n
-20
10
Ant
e
-90 -60 -30 0 30 60 90-30
A l
SCF01 Electronic Scanned Array DesignSlide 42
of 255
Angle
1-D Beam Formation (boresight)( g )
• Start with N elements equally spaced in a line– am represents the element factor
M 1
AF =
M!1Xm=0
amejkm"x sin 3 cos?
• Assume the am are equal and define Th h i h l d f f ll
m 0
A = k"x sin 3 cos?
• Then the summation has a closed form as follows
M!1X m 1!!ejA"M
AF = aXm=0
!e jA"m
=1
!e"
1 ! ejA
SCF01 Electronic Scanned Array DesignSlide 43
of 255
Maximum Gain
• The maximum value of AF is M and occurs whenever the denominator is zero.
[ / ]-
[ / ]-
AF =sin[MA/2]
sin(A/2)e jMA/2 |AF | =
---- sin[MA/2]
sin(A/2)
----sin(A/2) = 0 A/2 = n:
A = 2n:, n = 0,'1, . . .
SCF01 Electronic Scanned Array DesignSlide 44
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Selected Boresight Case (M=10)g ( )
10 10
4
6
8
10
λ = 3 cm
4
6
8
10
λ = 3 cm
-2
0
2
AF
-2
0
2
AF
-8
-6
-4
Δ x= 1 cmΔ x= 2 cm -8
-6
-4
Δ x= 1 cmΔ x= 2 cm
-90 -60 -30 0 30 60 90-10
θ
Δ x= 3 cm
-1 -0.5 0 0.5 1-10
u (sin θ)
Δ x= 3 cm
32
4 364
• Maxima occur at 3 = arcsin
32n:
k"x
4= arcsin
3n6
"x
4
SCF01 Electronic Scanned Array DesignSlide 45
of 255
1-D Beam Formation (steered)( )
• To steer the beam, we apply a linear phase (only) slope in the element weights
j k" i 3 ? j Aam = e!jmk"x sin 3s cos?s = e!jmAs
As = k"x sin 3s cos ?s
AF
M!1Xjkm"x sin 3 cos?AF =
Xm=0
amejkm"x sin 3 cos?
M 1
AF =
M!1Xm=0
e jkm"x(sin 3 cos?!sin 3s cos ?s)
SCF01 Electronic Scanned Array DesignPhase only (steering Spoiling, nulls, Sidelobes as-is)
m 0
Slide 46of 255
Scanned Array Factory
• Which reduces to
AF
M!1Xjm(A A )AF =
Xm=0
e jm(A!As)
AF =sin [M(A ! As)/2]
sin [(A ! As)/2]ejM(A!As)/2
[(A A )/ ]
-- sin[M (A ! As)/2]--|AF | =
--- sin[M (A As)/2]
sin[(A ! As)/2]
---SCF01 Electronic Scanned Array Design
Slide 47of 255
Selected Steered (30°) Case (M=10)( ) ( )
10
4
6
8
10
λ = 3 cm
2
4
6
8
10
λ = 3 cm
-2
0
2
4
AF
-8
-6
-4
-2
0AF
Δ x= 1 cmΔ x= 2 cm
-8
-6
-4
2
Δ x= 1 cmΔ x= 2 cm
-1 -0.5 0 0.5 1-10
u (sin θ)
Δ x= 3 cm
32
4 364-90 -60 -30 0 30 60 90
-10
θ
Δ x= 3 cm
3 = arcsin
32n:
k"x
4= arcsin
3n6
"x
4• Maxima occur at • Grating lobe for x = 3 cm
SCF01 Electronic Scanned Array Design
g
Slide 48of 255
Some Linear Arraysy
Single Element Three Element Eight ElementEight Element
Phase Shift
Σ
Σ
Σ
1
1.2
1 element linear array 0.8
13 element linear array0.5 λ element spacing0° steering angle
-1.9
0
0.8
18 element linear array0.5 λ element spacing0° steering angle
-1.9
0
)
0.8
18 element linear array0.5 λ element spacing30° steering angle
-1.9
0
0.2
0.4
0.6
0.8
Am
plitu
de
0.2
0.4
0.6
Am
plitu
de
-14.0
-8.0
-4.4
Alit
d(d
B)
0.2
0.4
0.6
Am
plitu
de
-14.0
-8.0
-4.4
Alit
d(d
B)
0.2
0.4
0.6
Am
plitu
de
-14.0
-8.0
-4.4
Alit
d(d
B)
SCF01 Electronic Scanned Array Design
-90 -60 -30 0 30 60 900
Angle-90 -60 -30 0 30 60 900
Angle0 -99 -90 -60 -30 0 30 60 900
Angle0 -99
-90 -60 -30 0 30 60 900
Angle0 -99
Slide 49of 255
More Elements Provide Better Performance
16 El
10
20
Beamwidth = 1.4°64 element linear array0.5 λ element spacing0° steering angle
B)
10
20
Beamwidth = 6.3°
16 element linear array0.5 λ element spacing0° steering angle
B)
10
20
Beamwidth = 3.0°
32 element linear array0.5 λ element spacing0° steering angle
B)
16 Element 32 Element 64 Element
-10
0
nten
na G
ain
(dB
-10
0
nten
na G
ain
(dB
-10
0
nten
na G
ain
(dB
-90 -60 -30 0 30 60 90-30
-20
Angle
An
-90 -60 -30 0 30 60 90-30
-20
Angle
An
-90 -60 -30 0 30 60 90-30
-20
Angle
An
• Gain improves - proportional to number of elements (array length)• Beamwidth improves - inversely proportional to number of elements
( l th)(array length)• Sidelobe magnitude is unchanged• At X-band (3 cm) and λ/2 spacing array lengths are about ¼ ½At X band (3 cm) and λ/2 spacing, array lengths are about ¼, ½,
and 1 meter respectivelySCF01 Electronic Scanned Array Design
Slide 50of 255
Linear Phased Array Exampley p
• Circles represent radiation from individual elements, which start at different times (or phases)
Equal Phase FrontBroadside
30° Scanned Beam
Radiating Elements
Phase Shifters orTime Delay Units
Feed Network
7 Δφ
7 Δτ
6 Δφ
6 Δτ
5 Δφ
5 Δτ
4 Δφ
4 Δτ
3 Δφ
3 Δτ
2 Δφ
2 Δτ
1 Δφ
1 Δτ
0 Δφ
0 ΔτΔτ = 50 psec
Antenna Inputent Spacing =3.0 cmWavelength = 3.0 cm
SCF01 Electronic Scanned Array DesignSlide 51
of 255
Limitations on Beam Formation
• ESAs which use phase shifters for steering have an additional design constraint relating aperture size and instantaneous bandwidth because of beam squintinstantaneous bandwidth because of beam squint– Time delay units have no inherent frequency limitation
• Element spacing of one-half wavelength provides fullElement spacing of one half wavelength provides full hemisphere steering without grating lobes– Between one-half and one wavelength spacing provides limited
steering volume without grating lobes– One wavelength or greater spacing results in grating lobe(s) at
all steering angles (including mechanical boresight)all steering angles (including mechanical boresight)
SCF01 Electronic Scanned Array DesignSlide 52
of 255
Beam steering: phase shift versus time delaydelay
Th b f ESA i t d f bl b l i• The beam of an ESA is steered preferably by applying a progressive time delay, Δτ, constant over frequency, across the antennas of the array. y
• Invariance of time delay with frequency is the primary characteristic of a true time delay (TTD) phase shifter or
ti d l it (TDU)a time delay unit (TDU). • Usage of TTD phase shifters avoids beam squinting or
frequency steeringfrequency steering.• The steering angle, θ, is expressed as a function of the
phase shift progression, β, which is a function of the p p g βfrequency and the progressive time delay, Δτ, which is invariant with frequency:
SCF01 Electronic Scanned Array DesignSlide 53
of 255
Phase Shifters cause Beam to Steer with Frequencywith Frequency
Phase shift at each element n 2 d/λ is dependent on• Phase shift at each element, n·2·π·d/λ, is dependent on frequency
• As the frequency changes, the beam moves and eventually ff th t tmoves off the target
• Bandwidth limitation for phase-only scanning is
"f K 6"f
f=
K " 6
L " sin(3)
• K is a factor approximately equal to one
• For L = 1 meter, λ = 3 cm and θ = 30°the resulting fractional bandwidth is6%
SCF01 Electronic Scanned Array DesignSlide 54
of 255
Time Delay Steeringy g
Required maximum time delay is equal to antenna length• Required maximum time delay is equal to antenna length times sine of the scan angle– Minimum time delay set by quantization requirements
N b f ti d l i l t b f l t• Number of time delays is equal to number of elements– Number of elements proportional to antenna length– Element spacing between 0.5 and 1.0 wavelengths
• Use cables to provide time delay– Have to make up cable loss with additional gain
• Total length of required cables is order ofo a e g o equ ed cab es s o de o
(L2 " sinazimuth "H2 " sin elevation)/62 = (Area2 " sinazimuth " sin elevation)/62
• Total cable mass (and volume) limits array size( ) y
SCF01 Electronic Scanned Array DesignSlide 55
of 255
Linear Phase Array with Time Delay –SteeredSteered
Broadside
• Proper time delay (50 picoseconds) between adjacent elements
30° Scanned Beam
adjacent elements• Generates beam in
desired direction (30°)
Radiating•Elements
desired•direction•(30 )
Phase•Shifters(modulo•2π)••
Feed Network
7•Δφ 6•Δφ 5•Δφ 4•Δφ 3•Δφ 2•Δφ 1•Δφ 0•Δφ Δφ•=•180°
Feed•Network
Antenna•InputElement•Spacing•=3.0•cm
Wavelength•=•3.0•cm
SCF01 Electronic Scanned Array DesignSlide 56
of 255
Linear Phase Array with Phase Shifters Unsteered– Unsteered
No phase shiftBroadside
• With no phase shift between elementsB i b d id
30° Scanned Beam
• Beam is broadside• Pattern null at 30°
Radiating Elements
Phase Shifters orTime Delay Units
Feed Network
7 Δφ
7 Δτ
6 Δφ
6 Δτ
5 Δφ
5 Δτ
4 Δφ
4 Δτ
3 Δφ
3 Δτ
2 Δφ
2 Δτ
1 Δφ
1 Δτ
0 Δφ
0 ΔτΔφ = 0°
Antenna InputElement Spacing =3.0 cm
Wavelength = 3.0 cm
SCF01 Electronic Scanned Array DesignSlide 57
of 255
Linear Phase Array with Phase Shifters Steered– Steered
Broadside
• Proper phase shift (180°) between adjacent elements
30° Scanned Beam
adjacent elements• Generates beam in
desired direction (30°)
Radiating Elements
desired direction (30 )
Phase Shifters(modulo 2π)
Feed Network
7 Δφ 6 Δφ 5 Δφ 4 Δφ 3 Δφ 2 Δφ 1 Δφ 0 Δφ Δφ = 180°
Feed Network
Antenna InputElement Spacing =3.0 cm
Wavelength = 3.0 cm
SCF01 Electronic Scanned Array DesignSlide 58
of 255
Wideband capabilitiesp
• Antenna selection determines waveform selection• Beamforming for wideband
– Slope/Step Chirp Waveforms– Amplitude/Frequency/Linear Frequency Modulation (chirp)
• Can spin phase shifters on transmit limits swath width if• Can spin phase shifters on transmit, limits swath width if used on receive
• Stretch = dechirp or deramp• Stretch = dechirp or deramp
SCF01 Electronic Scanned Array DesignSlide 59
of 255
Grating Lobes andGrating Lobes andThinned Arraysy
SCF01 Electronic Scanned Array DesignSlide 60
of 255
Grating Lobes and Thinned (sparse) ArraysArrays
A thi d b d fi d ith l t i >• A thinned array may be defined as an array with element spacing > λ– Resulting in grating lobes at all beam positions
G ti l b d d f b t itti i t d– Grating lobes degrade performance by transmitting power in unwanted directions/receiving noise and signals from unwanted directions
– Restricts addressable field of regardReduces cost and complexity– Reduces cost and complexity
– Also reduces electronic field of regard– ESA Fed reflector is a variant of this technique
Must mitigate (suppress) grating lobes to have a useable system• Must mitigate (suppress) grating lobes to have a useable system– Element pattern is primary technique
• Lattice spacing determines presence or absence as well as location f ti l bof grating lobes
• Radiating element must efficiently illuminate desired beam directions and suppress radiation in undesired beam directions
SCF01 Electronic Scanned Array DesignSlide 61
of 255
Grating Lobesg
G ti l b t i θ i θ λ/d h• Grating lobes occur at sin θp = sin θ0 + p·λ/d where– θP = grating lobe direction– θ0 = beam directionθ0 beam direction– λ = wavelength– d = element spacing
(1 2 3 )– p = ±(1,2,3, …)• Beam directions θ arcsin(λ/d-1) are free of grating
lobeslobes– If λ/d 1 (ie d λ) then all beam steering directions experience
grating lobesUltimate limit on beam scanning is θp = θ o (equal and– Ultimate limit on beam scanning is θp = - θ o (equal and opposite)
• sin θ0 = p·λ/(2·d)
SCF01 Electronic Scanned Array DesignSlide 62
of 255
Grating Lobes in u-v Space(Rectangular Lattice)(Rectangular Lattice)
2λ = 3.0 cm
1
ΔX = 2.3 cmΔY = 2.0 cm
(-2,1) (-1,1) (0,1) (1,1) (2,1)
os φ
)
0
V (s
in θ
⋅co
(-2,0) (-1,0) (1,0) (2,0)
-1
V
2
(-2,-1) (-1,-1) (0,-1) (1,-1) (2,-1)
SCF01 Electronic Scanned Array DesignSlide 63
of 255
-3 -2 -1 0 1 2 3-2
U (sin θ⋅sin φ)
Grating Lobes in u-v Space(Triangular Lattice)(Triangular Lattice)
2λ = 3.0 cm
1
ΔX = 2.3 cmΔY = 2.0 cm
(-2,1) (0,1)
os φ
)
(-1,1) (1,1)
0
V (s
in θ
⋅co
(-2,0)
-1
V
(-1,0) (1,0)
2
(-2,-1) (0,-1)
SCF01 Electronic Scanned Array DesignSlide 64
of 255
-3 -2 -1 0 1 2 3-2
U (sin θ⋅sin φ)
Scan Volume Comparisonp2
λ = 3.0 cm
Rectangular Case
1
ΔX = 2.3 cmΔY = 2.0 cm
Triangular CaseVisible Space
os φ
)
0
V (s
in θ
⋅co
-1
V
2
Rectangular Scan volume = 0.86 SteradiansTriangular Scan volume = 1.02 SteradiansTriangular lattice has 19.2% greater scan volume
SCF01 Electronic Scanned Array Design
-3 -2 -1 0 1 2 3-2
U (sin θ⋅sin φ) Slide 65of 255
Element Spacing > λ/2Grating LobesGrating Lobes
90g
Grating Lobe Onset (θ1)
75
s)
θ1 = asin(λ/Δx -1)θ = asin(λ/2Δx)
1
Grating Lobe Direction = Beam Direction (θ2)
60
n (d
egre
e θ2 = asin(λ/2Δx)
30
45
m D
irect
ion
← 41.8°
15
30
Bea
m
19.5° →
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 30
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3Element Center Spacing (in wavelengths)
SCF01 Electronic Scanned Array DesignSlide 66
of 255
Element Spacing > λ/2 GratingLobesLobes
Di l i t d l t l f i t• Dipole array oriented normal to plane of picture• Dipoles have uniform element pattern in plane of picture leading to pairs of mainlobes• For element spacing of λ/2, grating lobes appear only at 90° beam direction
8 elements, 0.5 λ apart
360° delta phase 0° beam direction
SCF01 Electronic Scanned Array DesignSlide 67
of 255
Element Spacing > λ/2 GratingLobesLobes
Di l i t d l t l f i t• Dipole array oriented normal to plane of picture• Dipoles have uniform element pattern in plane of picture leading to pairs of mainlobes• For element spacing of 0.75· λ, grating lobes appear only at > 19.5° beam direction
8 elements, 0.75 λ apart
360° delta phase 0° beam direction
SCF01 Electronic Scanned Array DesignSlide 68
of 255
Techniques for Grating Lobe SuppressionSuppression
• Restricted radiating element pattern will avoid feeding the grating lobes
This is almost always the case because elements larger than a– This is almost always the case because elements larger than a wavelength become directional
• Overlapped subarrayspp y• Introduce uncorrelated errors
– Redistributes•grating•lobe•radiation•so•that•the•peaks•are•g greduced•although•the•total•power•is•unaffected
SCF01 Electronic Scanned Array DesignSlide 69
of 255
Second PartSecond Part
SCF01 Electronic Scanned Array DesignSlide 70
of 255
Beam Pattern Synthesis
SCF01 Electronic Scanned Array DesignSlide 71
of 255
Optimizationp
• Sidelobe Disadvantages– Reduce gain in beam direction
Introduce target like artifacts– Introduce target-like artifacts– Introduce additional background (noise)
• Main beam shapingMain beam shaping
SCF01 Electronic Scanned Array DesignSlide 72
of 255
Amplitude Weighting (Taper) for Side Lobe ControlLobe Control
• Adjust gain at each element to optimize performance• Sidelobes may be reduced by reducing the power near
th d f ththe edge of the array– Reduces effective size of aperture and broadens beam
• Non uniform weighting in transmit is problematic• Non-uniform weighting in transmit is problematic– Element amplifiers operate near saturation– Reduces total radiated powerReduces total radiated power– Reduces aperture efficiency (area utilization)
• Aperture efficiencyp y
ATE =(P
m |am|)2M
Pm |am|2
SCF01 Electronic Scanned Array DesignSlide 73
of 255
Schelkunoff Representationp
• Schelkunoff assessed the excitation polynomial
M!1Xj (A A )AF =
Xm=0
amejm(A!As)
A = k"x sin 3, As = k"x sin 3s
z = e j(A!As)
AF =
M!1X0
amzm = aM
M!1Y0
(z ! zm)
SCF01 Electronic Scanned Array Design
m=0 m=0
Slide 74of 255
Single Beamg
C id th if ill i ti• Consider the uniform illumination caseAF = zM + zM!1 + zM!2 + ... + z2 + z + 1
MX M!1Ywhose roots are:
AF =Xm=0
zm =Ym=0
(z ! zm)
(2m!M!1):/M M dd 1 M 6 M + 1zm = e(2m!M):/M Meven,m = 1 : M,m 6= M
2
• One missing root with value of one. I t i i t
zm = e(2m M 1):/M Modd,m = 1 : M,m 6=2
• Insert missing root– Mainbeam disappears – only sidelobes left
AF ( 1)!
M M!1 M!2 2 1"
Slide 75of 255AF = zM+1 ! 1
AF = (z ! 1)!zM + zM 1 + zM 2 + ... + z2 + z + 1
"
Addition of Missing Rootg
12
λ = 3 cm
Uniform MethodImaginary
λ = 3 cm
Uniform Method
Unit Circle
8
10
Half PowerBeamwidth = 9.2°
M = 11Δx = 1.5 cm
olts
)
M = 11Δx = 1.5 cm
Unit CircleRootsBeam Space
2
4
6
AF
(vo
Real
-1 -0.5 0 0.5 10
u (sin θ)Aperture Taper Efficiency = 100.0%Aperture Taper Efficiency = 0.00 dB
Uniform MethodUniform MethodImaginary
λ = 3 cmM = 12Δx = 1.5 cm
Unit CircleRootsBeam Space
8
10
12
λ = 3 cmM = 12Δx = 1.5 cm
)
Real
4
6
AF
(vol
ts)
SCF01 Electronic Scanned Array DesignSlide 76
of 255Aperture Taper Efficiency = 16.7%
Aperture Taper Efficiency = -7.78 dB
-1 -0.5 0 0.5 10
2
u (sin θ)
Schelkunoff Theorems
• Theorem I: Every linear array with commensurable separations between the elements can be represented by a polynomial and everyelements can be represented by a polynomial and every polynomial can be interpreted as a linear array.
• Theorem II:There exists a linear array with a space factor equal to the product of the space factors of any two linear arrays.
Th III• Theorem III:The space factor of a linear array of n apparent elements is the product of the space factors of (n-1) virtual couplets with theirproduct of the space factors of (n 1) virtual couplets with their null points at the zeros of √Φ: t1, t2, … tn-1
SCF01 Electronic Scanned Array DesignSlide 77
of 255
Observations
Si A i l h it it d d ll t t• Since A is real, z has unit magnitude, and all roots must also have unit magnitude.
k"• For 0° 3 180°, A varies by 2k"x
• Roots may fall inside or outside of this range corresponding to nulls in real space or outside real spaceN ll l i h k ( id l b ) Th k l i• Nulls alternate with peaks (sidelobes). The peak value is smaller when nulls are closer. Grouping the nulls away from the main beam direction reduces the sidelobesfrom the main beam direction reduces the sidelobes while broadening the peak.
SCF01 Electronic Scanned Array DesignSlide 78
of 255
Sidelobe Control
• Binomial weighting– No sidelobes
Only practical for small number of elements– Only practical for small number of elements
• Dolph-Chebyshev weighting– Smallest beamwidth at first null for specified sidelobe level– Smallest beamwidth at first null for specified sidelobe level– All sidelobes are equal– Only practical for small number of elements
• Taylor /Bayliss weighting– Specify maximum sidelobe level and rate of falloff
SCF01 Electronic Scanned Array DesignSlide 79
of 255
Analytic Techniquesy q
U if W i hti• Uniform Weighting• Sidelobe Control
– Binomial weightingBinomial weighting• No sidelobes• Only practical for small number of elements
– Dolph-Chebyshev weightingDolph Chebyshev weighting• Smallest beamwidth at first null for specified sidelobe level• All sidelobes are equal• Only practical for small number of elementsOnly practical for small number of elements
– Taylor /Bayliss weighting• Specify maximum sidelobe level and rate of falloff
Beam shaping• Beam shaping– Fourier Synthesis– Woodward-Lawson
SCF01 Electronic Scanned Array DesignSlide 80
of 255
Uniform Weighting (unweighted)g g ( g )
• Simplest• Default condition for transmit• Highest gain
SCF01 Electronic Scanned Array DesignSlide 81
of 255
Uniform Example (M=11)p ( )
Uniform Method Uniform Method
-20
-15
-10
-5
0Half PowerBeamwidth = 9.2°λ•=•3•cm
M•=•11Δx•=•1.5•cm
B)
Imaginaryλ•=•3•cmM•=•11Δx•=•1.5•cm
•
Unit•CircleRootsBeam•Space
-45
-40
-35
-30
-25
Sidelobe•at•-15°
AF•
(dB
•Real
-90 -60 -30 0 30 60 90-50
Sidelobe•is•-13•dB
θAperture•Taper•Efficiency•=•100.0%Aperture•Taper•Efficiency•=•0.00•dB
•
0 9
1
λ•=•3•cm
Uniform•Method Root real imaginary magnitude angle
1 0 841 0 541i | 1 000 32 7°
0.5
0.6
0.7
0.8
0.9 M•=•11Δx•=•1.5•cm
cita
tion
1 0.841 + 0.541i | 1.000 32.7°
2 0.841 + -0.541i | 1.000 -32.7°
3 0.415 + 0.910i | 1.000 65.5°
4 0.415 + -0.910i | 1.000 -65.5°
i |
0 2 4 6 8 10 120
0.1
0.2
0.3
0.4
Aperture•Taper•Efficiency•=•100.0%Aperture•Taper•Efficiency•=•0.00•dB
Exc
5 -0.959 + 0.282i | 1.000 163.6°
6 -0.959 + -0.282i | 1.000 -163.6°
7 -0.655 + 0.756i | 1.000 130.9°
8 -0.655 + -0.756i | 1.000 -130.9°
|0 2 4 6 8 10 12
Element•Number 9 -0.142 + 0.990i | 1.000 98.2°
10 -0.142 + -0.990i | 1.000 -98.2°
SCF01 Electronic Scanned Array DesignSlide 82
of 255
Triangular Weightingg g g
• Zero at edges, unity in center, linear in-between• Special case of binomial (for three element array)• Array pattern is square of linear array pattern
– Autocorrelation of aperture weights
SCF01 Electronic Scanned Array DesignSlide 83
of 255
Triangular Example (M=11)g p ( )
Triangular Method Triangular Method
-20
-15
-10
-5
0Half PowerBeamwidth = 12.3°λ = 3 cm
M = 11Δx = 1.5 cm
B)
gImaginary
λ = 3 cmM = 11Δx = 1.5 cm
g
Unit CircleRootsBeam Space
-45
-40
-35
-30
-25
Sidelobe at -29°
AF
(dB
Real
-90 -60 -30 0 30 60 90-50
Sidelobe is -25 dB
θAperture Taper Efficiency = 80.7%
Aperture Taper Efficiency = -0.93 dB
0 9
1
λ = 3 cm
Triangular Method Root real imaginary magnitude angle
1 0 500 0 866i | 1 000 60 0°
0.5
0.6
0.7
0.8
0.9 M = 11Δx = 1.5 cm
cita
tion
1 0.500 + 0.866i | 1.000 60.0°
2 0.500 + -0.866i | 1.000 -60.0°
3 0.500 + 0.866i | 1.000 60.0°
4 0.500 + -0.866i | 1.000 -60.0°
i |
0 2 4 6 8 10 120
0.1
0.2
0.3
0.4
Aperture Taper Efficiency = 80.7%Aperture Taper Efficiency = -0.93 dB
Exc
5 -1.000 + 0.000i | 1.000 180.0°
6 -1.000 + 0.000i | 1.000 180.0°
7 -0.500 + 0.866i | 1.000 120.0°
8 -0.500 + -0.866i | 1.000 -120.0°
|0 2 4 6 8 10 12
Element Number 9 -0.500 + 0.866i | 1.000 120.0°
10 -0.500 + -0.866i | 1.000 -120.0°
SCF01 Electronic Scanned Array DesignSlide 84
of 255
Binomial Weightingg g
• Positioning all of the nulls at the edge of the scan volume, ie A=0 so that zm=1 for all m creates a beam pattern with no sidelobes This is termed the binomialpattern with no sidelobes. This is termed the binomial array.
• Illumination factor goes to zero at the edge of the arrayIllumination factor goes to zero at the edge of the array• First proposed by John Stone Stone in United States
Patents 1,643,323 and 1,715,433a e s ,6 3,3 3 a d , 5, 33
SCF01 Electronic Scanned Array DesignSlide 85
of 255
Binomial Example (M=11)p ( )
Binomial Method Binomial Method
-20
-15
-10
-5
0Half PowerBeamwidth = 19.1°λ = 3 cm
M = 11Δx = 1.5 cm
B)
Imaginaryλ = 3 cmM = 11Δx = 1.5 cm
Unit CircleRootsBeam Space
-45
-40
-35
-30
-25
Sidelobe at -81°
AF
(dB
Real
-90 -60 -30 0 30 60 90-50
Sidelobe is -326 dB
θAperture Taper Efficiency = 51.6%
Aperture Taper Efficiency = -2.87 dB
0 9
1
λ = 3 cm
Binomial Method Root real imaginary magnitude angle
1 1 046 0 000i | 1 046 180 0°
0.5
0.6
0.7
0.8
0.9 M = 11Δx = 1.5 cm
cita
tion
1 -1.046 + 0.000i | 1.046 180.0°
2 -1.038 + 0.027i | 1.038 178.5°
3 -1.038 + -0.027i | 1.038 -178.5°
4 -1.015 + 0.044i | 1.016 177.5°
i |
0 2 4 6 8 10 120
0.1
0.2
0.3
0.4
Aperture Taper Efficiency = 51.6%Aperture Taper Efficiency = -2.87 dB
Exc
5 -1.015 + -0.044i | 1.016 -177.5°
6 -0.986 + 0.045i | 0.987 177.4°
7 -0.986 + -0.045i | 0.987 -177.4°
8 -0.962 + 0.028i | 0.963 178.4°
|0 2 4 6 8 10 12
Element Number 9 -0.962 + -0.028i | 0.963 -178.4°
10 -0.953 + 0.000i | 0.953 180.0°
SCF01 Electronic Scanned Array DesignSlide 86
of 255
Dolph-Chebyshevp y
• Provides the narrowest beamwidth (at first null) for specified sidelobe level or lowest sidelobe level for specified beamwidthspecified beamwidth
• This technique matches the roots of a Chebyshev polynomial with the roots of the aperture illuminationpolynomial with the roots of the aperture illumination function.
SCF01 Electronic Scanned Array DesignSlide 87
of 255
Chebyshev Polynomialsy y
0
1
2
m
m = 1m = 2m = 3m = 4m = 5
2
-1
0T m
m = 6m = 7m = 8m = 9m = 10
-1.5 -1 -0.5 0 0.5 1 1.5-2
x
Tm(x) = cos(m cos!1 x) |x| 5 1
( ) ( 1 )Tm(x) = cosh(m cosh!1 x) x > 1
T (x) = ( 1)m cosh(m cosh!1 x) x < 1
SCF01 Electronic Scanned Array Design
Tm(x) = (!1) cosh(m cosh x) x < !1Slide 88
of 255
Aperture Weight Derivationp g
AF =
M!1X0
amejkm"x sin 3 cos?
m=0
AF (3) (jk (M + 1)/2" i 3)
(M!1)/2X(jk " i 3)AF (3) = exp (jk0 (M + 1)/2"x sin 3)
X!(M!1)/2
amexp(jk0m"x sin 3)
(M 1)/2
AF (3) =
(M!1)/2X!(M!1)/2
amexp(jk0m"xsin 3)
AF (3) = a0 +
(M!1)/2X1
amcos(2m cos!1x)
SCF01 Electronic Scanned Array Design
1
Slide 89of 255
Result
• For M odd
am =
MXTM!1
3c cos
Ai
2
4cos (mAi)
• For M even
m
Xi=1
M 1
32
4( Ai)
am =
MXi=1
TM!1
3c cos
Ai
2
4cos
33m!
1
2
4Ai
4
• c is a function of the sidelobe ratio R
i=1
c = cosh
3cosh!1(R)
M ! 1
4
SCF01 Electronic Scanned Array Design
3 4Slide 90
of 255
Dolph-Chebyshev Example (M=11)p y p ( )
Chebychev Method Chebychev Method
-20
-15
-10
-5
0Half PowerBeamwidth = 10.1°λ = 3 cm
M = 11R = 20 dB
B)
yImaginary
λ = 3 cmM = 11R = 20 dB
y
Unit CircleRootsBeam Space
-45
-40
-35
-30
-25
Sidelobe at -16°
AF
(dB
Real
-90 -60 -30 0 30 60 90-50
Sidelobe is -20 dB
θAperture Taper Efficiency = 96.4%
Aperture Taper Efficiency = -0.16 dB
0 9
1
λ = 3 cm
Chebychev Method Root real imaginary magnitude angle
1 0 786 0 618i | 1 000 38 2°
0.5
0.6
0.7
0.8
0.9 M = 11R = 20 dB
cita
tion
1 0.786 + 0.618i | 1.000 38.2°
2 0.454 + 0.891i | 1.000 63.0°
3 -0.085 + 0.996i | 1.000 94.8°
4 -0.623 + 0.783i | 1.000 128.5°
i |
0 2 4 6 8 10 120
0.1
0.2
0.3
0.4
Aperture Taper Efficiency = 96.4%Aperture Taper Efficiency = -0.16 dB
Exc
5 -0.955 + 0.296i | 1.000 162.8°
6 -0.955 + -0.296i | 1.000 -162.8°
7 -0.623 + -0.783i | 1.000 -128.5°
8 0.786 + -0.618i | 1.000 -38.2°
|0 2 4 6 8 10 12
Element Number 9 0.454 + -0.891i | 1.000 -63.0°
10 -0.085 + -0.996i | 1.000 -94.8°
SCF01 Electronic Scanned Array DesignSlide 91
of 255
Taylor Weightingy g g
• Taylor modified the Dolph-Chebyshev, retaining the near sidelobe structure (and polynomial zeros) and modifying the far sidelobe structure (and polynomial zeros) to usethe far sidelobe structure (and polynomial zeros) to use the zeros of the sinx/x function which has lower far sidelobes.
• The transition between the two functions is based on two parameters σ and n-bar where σ is the scale factor for the Dolph-Chebyshev function and n-bar is the number of Dolph-Chebyshev equal sidelobes. .
SCF01 Electronic Scanned Array DesignSlide 92
of 255
Taylor Example (M=11)y p ( )
Taylor Method Taylor Method
-20
-15
-10
-5
0Half PowerBeamwidth = 10.1°λ = 3 cm
M = 11R = 20 dBn-bar = 5
B)
yImaginary
λ = 3 cmM = 11R = 20 dBn-bar = 5
y
Unit CircleRootsBeam Space
-45
-40
-35
-30
-25
Sidelobe at -16°
AF
(dB
Real
-90 -60 -30 0 30 60 90-50
Sidelobe is -20 dB
θAperture Taper Efficiency = 96.3%
Aperture Taper Efficiency = -0.16 dB
0 9
1
λ = 3 cm
Taylor Method Root real imaginary magnitude angle
1 0 959 0 282i | 1 000 163 6°
0.5
0.6
0.7
0.8
0.9 M = 11R = 20 dBn-bar = 5
cita
tion
1 -0.959 + 0.282i | 1.000 163.6°
2 -0.959 + -0.282i | 1.000 -163.6°
3 -0.630 + 0.777i | 1.000 129.0°
4 -0.630 + -0.777i | 1.000 -129.0°
i |
0 2 4 6 8 10 120
0.1
0.2
0.3
0.4
Aperture Taper Efficiency = 96.3%Aperture Taper Efficiency = -0.16 dB
Exc
5 -0.090 + 0.996i | 1.000 95.2°
6 -0.090 + -0.996i | 1.000 -95.2°
7 0.785 + 0.619i | 1.000 38.3°
8 0.785 + -0.619i | 1.000 -38.3°
|0 2 4 6 8 10 12
Element Number 9 0.451 + 0.893i | 1.000 63.2°
10 0.451 + -0.893i | 1.000 -63.2°
SCF01 Electronic Scanned Array DesignSlide 93
of 255
Beam Shaping / Spoilingp g p g
• Previous methods developed for sidelobe control• Following methods deal with main beam• General problem is to form a shaped beam
– Broad beams in azimuth direction desired for SARCosecant beams sef l for air s r eillance radars here range– Cosecant beams useful for air surveillance radars where range varies with elevation angle
SCF01 Electronic Scanned Array DesignSlide 94
of 255
Fourier Synthesis Techniquey q
• Since the beam shape is the Fourier transform of the illumination function, take the inverse Fourier transform of the beam shape to obtain the required illuminationof the beam shape to obtain the required illumination function– However, this produces an illumination function infinite in extent, p– Possible to truncate the computed illumination function but that
produces ripples in the beam shape
SCF01 Electronic Scanned Array DesignSlide 95
of 255
Fourier Transform Synthesisy
T f d i d b h i t t l i ldi• Transform desired beamshape into aperture plane, yielding excitation coefficients for an infinite area
d6/(2dx)Z
an =dx
6
Z!6/(2dx)
F (u) exp!j(2:/6)undx du
• For rectangular beamshape, resulting excitation is a sinc function
• Synthesize beam shape based on finite limitsSynthesize beam shape based on finite limits• Ripple is termed Gibbs phenomena• Aperture needs to be long enough to encompass several
zeros of the sinc in order to produce an approximately rectangular beam– Efficiency suffersc e cy su e s
SCF01 Electronic Scanned Array DesignSlide 96
of 255
Fourier Transform – First Null
Fourier Method Fourier Method
-20
-15
-10
-5
0Half PowerBeamwidth = 13.6°λ = 3 cm
M = 14Δx = 1.5 cm
B)
Imaginary = 3 cm
M = 14Δx = 1.5 cm
Unit CircleRootsSynthesized BeamBeam Space
-45
-40
-35
-30
-25
Sidelobe at -19°
AF
(dB
Real
-90 -60 -30 0 30 60 90-50
Sidelobe is -22 dB
θAperture Taper Efficiency = 67.3%
Aperture Taper Efficiency = -1.72 dB
0 9
1
λ = 3 cm
Fourier Method
Root real imaginary magnitude angle1 2.624 + -0.000i | 2.624 -0.0°2 0.657 + 0.754i | 1.000 48.9°3 0.260 + 0.966i | 1.000 74.9°
0.5
0.6
0.7
0.8
0.9 M = 14Δx = 1.5 cm
cita
tion
4 -0.196 + 0.981i | 1.000 101.3°5 -0.610 + 0.793i | 1.000 127.6°6 -0.897 + 0.441i | 1.000 153.8°7 -1.000 + -0.000i | 1.000 -180.0°8 -0.897 + -0.441i | 1.000 -153.8°9 -0 610 + -0 793i | 1 000 -127 6°
0 5 10 150
0.1
0.2
0.3
0.4
Aperture Taper Efficiency = 67.3%Aperture Taper Efficiency = -1.72 dB
Exc 9 0.610 + 0.793i | 1.000 127.6
10 -0.196 + -0.981i | 1.000 -101.3°11 0.260 + -0.966i | 1.000 -74.9°12 0.657 + -0.754i | 1.000 -48.9°13 0.381 + 0.000i | 0.381 0.0°
0 5 10 15
Element Number
SCF01 Electronic Scanned Array DesignSlide 97
of 255
Fourier Transform – Second Null
Fourier Method Root real imaginary magnitude angle
-20
-15
-10
-5
0Half PowerBeamwidth = 16.9°λ = 3 cm
M = 25Δx = 1.5 cm
B)
Root real imaginary magnitude angle1 3.098 + -0.000i | 3.098 -0.0°2 1.332 + 0.000i | 1.332 0.0°3 0.758 + 0.653i | 1.000 40.7°4 0.573 + 0.820i | 1.000 55.1°5 0.346 + 0.938i | 1.000 69.8°
-45
-40
-35
-30
-25
Sidelobe at -15°
AF
(dB |
6 0.095 + 0.995i | 1.000 84.6°7 -0.162 + 0.987i | 1.000 99.3°8 -0.407 + 0.913i | 1.000 114.0°9 -0.625 + 0.780i | 1.000 128.7°
10 -0.803 + 0.597i | 1.000 143.4°
-90 -60 -30 0 30 60 90-50
Sidelobe is -23 dB
θ
1
3
Fourier Method
|11 -0.927 + 0.374i | 1.000 158.0°12 -0.992 + 0.127i | 1.000 172.7°13 -0.992 + -0.127i | 1.000 -172.7°14 -0.927 + -0.374i | 1.000 -158.0°15 -0.803 + -0.597i | 1.000 -143.4°
0.5
0.6
0.7
0.8
0.9λ = 3 cmM = 25Δx = 1.5 cm
tatio
n
16 -0.625 + -0.780i | 1.000 -128.7°17 -0.407 + -0.913i | 1.000 -114.0°18 -0.162 + -0.987i | 1.000 -99.3°19 0.095 + -0.995i | 1.000 -84.6°20 0.346 + -0.938i | 1.000 -69.8°
0
0.1
0.2
0.3
0.4
Aperture Taper Efficiency = 52.5%Aperture Taper Efficiency = -2.80 dB
Exci
t
21 0.573 + -0.820i | 1.000 -55.1°22 0.758 + -0.653i | 1.000 -40.7°23 0.751 + 0.000i | 0.751 0.0°24 0.323 + -0.000i | 0.323 -0.0°
0 5 10 15 20 250
Element Number
SCF01 Electronic Scanned Array DesignSlide 98
of 255
Fourier Transform – Third Null
Fourier MethodRoot real imaginary magnitude angle
1 5.722 + 0.000i | 5.722 0.0°
-20
-15
-10
-5
0Half PowerBeamwidth = 17.8°λ = 3 cm
M = 36Δx = 1.5 cm
B)
|2 1.196 + -0.234i | 1.219 -11.1°3 1.196 + 0.234i | 1.219 11.1°4 0.792 + -0.611i | 1.000 -37.7°5 0.676 + -0.737i | 1.000 -47.5°6 0.536 + -0.844i | 1.000 -57.6°7 0.378 + -0.926i | 1.000 -67.8°8 0.208 + -0.978i | 1.000 -78.0°
-45
-40
-35
-30
-25
Sidelobe at -13°
AF
(dB
9 0.031 + -1.000i | 1.000 -88.2°10 -0.147 + -0.989i | 1.000 -98.4°11 -0.320 + -0.947i | 1.000 -108.7°12 -0.483 + -0.876i | 1.000 -118.9°13 -0.630 + -0.776i | 1.000 -129.1°14 -0.758 + -0.653i | 1.000 -139.3°15 -0.861 + -0.508i | 1.000 -149.5°16 0 938 + 0 348i | 1 000 159 6°
-90 -60 -30 0 30 60 90-50
Sidelobe is -23 dB
θ
1
3
Fourier Method
16 -0.938 + -0.348i | 1.000 -159.6°17 -0.984 + -0.177i | 1.000 -169.8°18 -1.000 + 0.000i | 1.000 180.0°19 -0.984 + 0.177i | 1.000 169.8°20 -0.938 + 0.348i | 1.000 159.6°21 -0.861 + 0.508i | 1.000 149.5°22 -0.758 + 0.653i | 1.000 139.3°23 -0.630 + 0.776i | 1.000 129.1°
0.5
0.6
0.7
0.8
0.9λ = 3 cmM = 36Δx = 1.5 cm
tatio
n
3 0.630 0. 6 | .000 9.24 -0.483 + 0.876i | 1.000 118.9°25 -0.320 + 0.947i | 1.000 108.7°26 -0.147 + 0.989i | 1.000 98.4°27 0.031 + 1.000i | 1.000 88.2°28 0.208 + 0.978i | 1.000 78.0°29 0.378 + 0.926i | 1.000 67.8°30 0.536 + 0.844i | 1.000 57.6°
0
0.1
0.2
0.3
0.4
Aperture Taper Efficiency = 43.5%Aperture Taper Efficiency = -3.62 dB
Exci
t
31 0.676 + 0.737i | 1.000 47.5°32 0.792 + 0.611i | 1.000 37.7°33 0.805 + -0.158i | 0.820 -11.1°34 0.805 + 0.158i | 0.820 11.1°35 0.175 + 0.000i | 0.175 0.0°
0 5 10 15 20 25 30 350
Element Number
SCF01 Electronic Scanned Array DesignSlide 99
of 255
Woodward-Lawson Synthesisy
• Starts with basis functions for beam shape based on a finite apertureB i f ti if l i ht d b t d t• Basis functions are uniformly weighted beams steered at increments of 2π/M with the result that nulls coincide
• This allows a direct computation of weights to• This allows a direct computation of weights to approximate any desired beam shape– Technique modified by Elliot in 1968Technique modified by Elliot in 1968
SCF01 Electronic Scanned Array DesignSlide 100
of 255
Combine Beams 5, 6 and 7
Woodward Method
10
12
λ = 3 cmM = 11Δx = 1 5 cm
Woodward Method
6
8Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°
Δx 1.5 cm
s)
2
4
AF
(vol
ts
0
2A
-1 -0.5 0 0.5 1-4
-2
u (sin θ)u (sin θ)
SCF01 Electronic Scanned Array DesignSlide 101
of 255
Woodward-Lawson Examplep
Woodward Method Woodward Method
-20
-15
-10
-5
0Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°Half PowerBeamwidth = 27.7°λ = 3 cm
M = 11Δx = 1.5 cm
B)
Beam -5Beam -4Beam -3Beam -2Beam -1Beam 0Beam 1Beam 2Beam 3
Imaginaryλ = 3 cmM = 11Δx = 1.5 cm
Unit CircleRootsSynthesized BeamBeam Space
-45
-40
-35
-30
-25
Sidelobe at -26°
AF
(dB Beam 4
Beam 5 Real
-90 -60 -30 0 30 60 90-50
Sidelobe is -15 dB
θ
0 9
1
λ = 3 cm
Woodward Method Root real imaginary magnitude angle
1 1 785 0 000i | 1 785 0 0°
0.5
0.6
0.7
0.8
0.9 M = 11Δx = 1.5 cm
cita
tion
1 1.785 + 0.000i | 1.785 0.0°
2 -0.959 + 0.282i | 1.000 163.6°
3 -0.959 + -0.282i | 1.000 -163.6°
4 -0.655 + 0.756i | 1.000 130.9°
i |
0 2 4 6 8 10 120
0.1
0.2
0.3
0.4
Woodward-Larson Efficiency = 69.8%Woodward-Larson Efficiency = -1.56 dB
Exc
5 -0.655 + -0.756i | 1.000 -130.9°
6 -0.142 + 0.990i | 1.000 98.2°
7 -0.142 + -0.990i | 1.000 -98.2°
8 0.415 + 0.910i | 1.000 65.5°
|0 2 4 6 8 10 12
Element Number 9 0.415 + -0.910i | 1.000 -65.5°
10 0.560 + 0.000i | 0.560 0.0°
SCF01 Electronic Scanned Array DesignSlide 102
of 255
Quadratic Beam Spoilingp g
• Not a synthesis technique• Apply systematic phase error at each element
SCF01 Electronic Scanned Array DesignSlide 103
of 255
Additional Phase Term
Quadratic Phase Method
140
160
λ = 3 cmM = 11Δx = 1 5 cm
Quadratic Phase Method
100
120
Δx 1.5 cm
egre
es)
60
80
Ang
le (d
40
60
Pha
se A
0 2 4 6 8 10 120
20 Aperture Taper Efficiency = 100.0%Aperture Taper Efficiency = 0.00 dB
Element NumberElement Number
SCF01 Electronic Scanned Array DesignSlide 104
of 255
Quadratic Phase Examplep
Quadratic Phase Method Quadratic Phase Method
-20
-15
-10
-5
0Half PowerBeamwidth = 26.7°λ = 3 cm
M = 11Δx = 1.5 cm
B)
Imaginaryλ = 3 cmM = 11Δx = 1.5 cm
Unit CircleRootsBeam Space
-45
-40
-35
-30
-25
Sidelobe at -25°
AF
(dB
Real
-90 -60 -30 0 30 60 90-50
Sidelobe is -6 dB
θAperture Taper Efficiency = 100.0%Aperture Taper Efficiency = 0.00 dB
0 9
1
λ = 3 cm
Quadratic Phase Method Root real imaginary magnitude angle
1 1 231 0 482i | 1 322 21 4°
0.5
0.6
0.7
0.8
0.9 M = 11Δx = 1.5 cm
cita
tion
1 1.231 + 0.482i | 1.322 21.4°
2 0.556 + 1.052i | 1.190 62.1°
3 -0.138 + 1.099i | 1.107 97.2°
4 -0.686 + 0.801i | 1.055 130.6°
i |
0 2 4 6 8 10 120
0.1
0.2
0.3
0.4
Aperture Taper Efficiency = 100.0%Aperture Taper Efficiency = 0.00 dB
Exc
5 -0.975 + 0.288i | 1.017 163.6°
6 -0.943 + -0.278i | 0.984 -163.6°
7 -0.617 + -0.720i | 0.948 -130.6°
8 -0.113 + -0.896i | 0.903 -97.2°
|0 2 4 6 8 10 12
Element Number 9 0.392 + -0.743i | 0.840 -62.1°
10 0.704 + -0.276i | 0.756 -21.4°
SCF01 Electronic Scanned Array DesignSlide 105
of 255
Beam Shape Comparisons11 Element* Linear Array11 Element* Linear Array
h d id h ffi i i Sid l bMethod Beamwidth Efficiency First Sidelobe
Uniform 9.2° 100% -13 dB
Triangular 12 3° 80 7% -25 dBTriangular 12.3 80.7% 25 dB
Binomial 19.1° 51.6% None
Dolph-Chebyshev 10.1° 96.4% -20 dB
Taylor (n-bar=5) 10.1° 96.3% -20 dB
Fourier Reconstruction to First Null 13.6° 67.3% -22 dB
Fourier Reconstruction to Second Null
16.9° 52.5% -23 dB
Fourier Reconstruction to Third Null 17.8° 43.5% -23 dB
Woodward-Larson 27.7° 69.8% -15 dB
Quadratic Phase (maximum 150°) 26.7° 100% -6 dB
SCF01 Electronic Scanned Array Design
* Fourier Reconstructions Required 14, 25, and 36 elements respectivelySlide 106
of 255
Summaryy
• The effect of taper is similar for transmit and receive and is captures in η, the aperture taper efficiency
The effect may be described as a reduction in effective area of– The effect may be described as a reduction in effective area of the aperture with the provision that the sidelobes improve, rather than degrade with the smaller effective area
– The beamwidth broadens however commensurate with the reduced area
• Note that the examples given are one dimensional• Note that the examples given are one dimensional arrays– The taper efficiency must be squared to represent a two p y q p
dimensional array
SCF01 Electronic Scanned Array DesignSlide 107
of 255
Subarray partitioning and recombinationrecombination
It i f tl i t t f l f• It is frequently convenient to form a large array as an array of smaller arrays (subarrays)– Think of replacing the element (pattern) with a subarray (pattern)– In the boresight (nonsteered) case the two are indistinguishable
• Thinned arrays may be constructed using non-steered subarrays connected to a fewer number of tr modulessubarrays connected to a fewer number of tr modules– The non-steered subarray will have nulls matching the grating lobes
of the array factor of the thinned array on boresightThe grating lobes will reappear as soon as the beam is steered off– The grating lobes will reappear as soon as the beam is steered off boresight
• Subarrays may be phase steered and combined using time d l t hi id i t t b d idthdelay to achieve wider instantaneous bandwidth– The steered subarray will keep its nulls (approximately) aligned with
the grating lobes of the array factor of the thinned array
SCF01 Electronic Scanned Array DesignSlide 108
of 255
Array of Arraysy y
• Some arrays are formed from a collection of smaller arrays, termed subarrays
This is a cost/complexity based design decision– This is a cost/complexity based design decision– The performance may be assessed by using the subarray
pattern as the element pattern in the analysis – The array will have a lattice spacing >> λ/2 which would
ordinarily create excessive sidelobesThe concept of pattern multiplication applies and the nulls in the– The concept of pattern multiplication applies and the nulls in the element pattern tend to coincide with the grating lobes of the array
SCF01 Electronic Scanned Array DesignSlide 109
of 255
Beamforming (feed networks)g ( )
S i F d• Series Fed– Path length to different elements is different introducing a frequency
dependent phase shift with the result that the beam direction will h ith fchange with frequency
• Corporate– More complicated but equal path lengths to all elements eliminates p q p g
beam steering with frequency• Butler Matrix
NxN inputs and output are combined and recombined to introduce– NxN inputs and output are combined and recombined to introduce phase shifts which provide multiple simultaneous orthogonal beams
– Iridium uses this techniqueBl M t i• Blass Matrix– NxM inputs and output are combined and recombined to introduce
path length differences which provide multiple simultaneous beams
SCF01 Electronic Scanned Array DesignSlide 110
of 255
Tolerances and Errors
• Examples drawn in Matlab with ~ 16 decimal digits of precisionR l h d i 1 %• Real hardware accuracy is ~1 %
• Need to assess effect of errors on theoretical performanceperformance– Array flatness– Electrical length of multiple paths requires calibration andElectrical length of multiple paths requires calibration and
possibly recalibration– Gain and Phase control errors and quantization– Deployment to final configuration
SCF01 Electronic Scanned Array DesignSlide 111
of 255
Random Phase and Amplitude Errorsp
• The antenna designer can readily compute by means of standard synthesis methods the aperture excitation necessary for a desired radiation pattern Howevernecessary for a desired radiation pattern. However, when he constructs his antenna and measures its performance he finds that his experimental pattern only p p p yapproximates the theoretical one.– John Ruze 1951
SCF01 Electronic Scanned Array DesignSlide 112
of 255
Error Analysis by Ruzey y
S t t l fi ld it ti i t id l fi ld it ti d• Separate actual field excitations into ideal field excitation and error field excitation
• If errors are uncorrelated then the power from each excitation pare additive– Error term raises the noise floor
• Correlated errors are introduced by quantization• Correlated errors are introduced by quantization– Error term introduces additional peaks (sidelobes) in the pattern
• For relatively small errors, the expected rms error is y p
702 = 7"2 + /2
where Δ is the amplitude error (relative) and δ is the phase error (radians)error (radians)
SCF01 Electronic Scanned Array DesignSlide 113
of 255
Reflector Applications
SCF01 Electronic Scanned Array DesignSlide 114
of 255
Types of Reflector Systems(Optical Analogs)(Optical Analogs)
P i S dPrimary Secondary
Near Field Cassegrainian Parabolic Parabolic
Confocal Cassegrainian Parabolic HyperbolicConfocal Cassegrainian Parabolic Hyperbolic
Gregorian Parabolic Ellipsoidal
Ritchey-Chrétien Hyperbolic Hyperbolic
• All are “perfect” on axis, different aberrations off axisAll are perfect on axis, different aberrations off axis• Design trades include
– Focal planep– Feed position (at or off focal point)– On-axis or offset feed
SCF01 Electronic Scanned Array DesignSlide 115
of 255
ESA Fed Reflector
C bi f th b fit ( d f th• Combines some of the benefits (and some of the disadvantages) of ESAs and reflectors
• ESA feeds are useful with both cylindrical (1 dimensionalESA feeds are useful with both cylindrical (1 dimensional curvature) and parabolic reflectors (2 dimensional curvature)
• Basic trade-off is to exchange electronic field of regard (EFOR) for fewer t/r modules
Analogous to thinned array– Analogous to thinned array– Reduces cost by substituting mechanical structure (reflector) for
electronics• Approach used by Thuraya communications satellite,
selected for DESDynI, used in radio telescopes (receive only)only)
SCF01 Electronic Scanned Array DesignSlide 116
of 255
Beam Steered (Switched) Reflector( )
S l t f d t d t i i ti di ti• Select feed to determine pointing direction– Used by Israeli TecSAR system
Only one element contributes power to each beam direction– Only one element contributes power to each beam direction
Parabolic reflector
Feed
Focal Plane
Feed
SCF01 Electronic Scanned Array DesignSlide 117
of 255
ESA Fed Reflector(Phased Array Fed Reflector)(Phased Array Fed Reflector)
ESA f d bl k f th b fl t d ff th fl t• ESA feed blocks some of the beam reflected off the reflector• Feed at focal plan uses only one element per beam• Move feed off focal plane so that multiple elements contribute to beam• Problem using all elements for all beams (efficiency) illuminating the entire reflector
Parabolic reflector
Focal Plane
ES
AE
SCF01 Electronic Scanned Array DesignSlide 118
of 255
When is an ESA Fed Reflector useful
• Expensive T/R modules– Cost (1000 P watt modules) < Cost (100,000 P/100 watt
modules)modules)– 1000 x $2,000 = $2 million– 100,000 x $200 = $20 million
• Small Electronic Field of View is all that is required– Electronic steering limited to about 10% so addressable volume
li i d b 1%limited to about 1%
• Still need to dissipate the same amount of heat since module efficiencies are comparablemodule efficiencies are comparable
SCF01 Electronic Scanned Array DesignSlide 119
of 255
ESA Fed Reflector Design Challengesg g
• Efficient use of resources– Either ESA Feed or Reflector is oversized
Sid l b d t t bl k• Sidelobes due to aperture blockage• Beam quality degrades with scan
El t i fi ld f d i it ll l ti t ESA• Electronic field of regard is quite small relative to ESA• Thermal problems are exacerbated (unless power is
limited)limited)
SCF01 Electronic Scanned Array DesignSlide 120
of 255
Geometrical Interpretationp
• Unfold the reflector system and• Unfold the reflector system and the similarity to a thinned array is obvious
• Comparing a ESA fed reflectorComparing a ESA fed reflector to a fully populated phased array is the wrong comparison
• Take the TR cells in the ESA f d d d th t t thfeed and spread them out to the same area as the primary reflector
• Then the electronic scanThen the electronic scan capabilities are similar and the costs differ only by the cost of the structure and cablingH th l t i• However, the electronic scan capability of the thinned array is superior as it is not limited by vignetting or geometric distortiong g g
SCF01 Electronic Scanned Array DesignSlide 121
of 255
Grating Lobe Limit of Unfolded Systemg y
• Assume feed element spacing is λ/2• Fitzgerald’s reflector system has magnification factor of 4• Analogous thinned array has element spacing 4•λ/2 = 2λ• Maximum scan angle is
– sin θo = p·λ/(2·d) (ref slide 57)or
– sin θo = 1·λ/(2· 2λ) = ¼sin θo 1 λ/(2 2λ) ¼
• So θo= 14° (considerably better (2-3X) than limit imposed by vignetting)p y g g)
SCF01 Electronic Scanned Array DesignSlide 122
of 255
PART THREEPART THREE
SCF01 Electronic Scanned Array DesignSlide 123
of 255
Practical Designg
• Theory in Matlab with high precision and no errors• Need to approximate ideal components• Electronics advances have made this possible
SCF01 Electronic Scanned Array DesignSlide 124
of 255
ESA Challengesg
• Constituent Parts– Radiating Elements (mutual coupling)
TR Modules– TR Modules– Beam Control– Microwave Distribution and PWBs
• Thermal Control (Active / passive)• Integration and Testeg a o a d es• Technology Base• CostCost
SCF01 Electronic Scanned Array DesignSlide 125
of 255
Radiating Elements
SCF01 Electronic Scanned Array DesignSlide 126
of 255
Element types for arraysyp y
P i f ti i t di t ll li d• Primary function is to radiate all applied power– Element match (return loss Γ or S11 is critical metric)
• Current arrays use• Current arrays use– Patch elements– Dipole elements– Notch elements– Slotted waveguides– Horns (for widely spaced arrays)Horns (for widely spaced arrays)
• Element behavior changes when the element is installed in an array with adjacent elements due to mutual coupling– Some power coupled into adjacent elements and reradiated
SCF01 Electronic Scanned Array DesignSlide 127
of 255
Mutual Coupling Effectsp g
• Reduces element Q (broader bandwidth)– Coupled dipole arrays offer very good performance
C t t d d ( bli d )• Creates unexpected modes (scan blindness)– Coupled power can negate drive power
• No general analytic solutions• No general analytic solutions• Array size determines approach
Very small arrays may be modeled numerically– Very small arrays may be modeled numerically– Infinite arrays may be modeled using periodic boundary
conditions
SCF01 Electronic Scanned Array DesignSlide 128
of 255
Radiating Element Requirementg q
• Wide angle radiation pattern• Low cost• Readily arrayed• Compatibility with feed and t/r modules
SCF01 Electronic Scanned Array DesignSlide 129
of 255
Efficiencyy
• Mutual•coupling• If•the•transmit•power•is•not•radiated•or•receive•power•is•
t b b d b th tnot•absorbed•by•the•antenna• Then•it•is•scattered•back•to•the•source
Th di t tt i t S11 tifi thi• The•radiator•scattering•parameter•S11•quantifies•this•reflection
SCF01 Electronic Scanned Array DesignSlide 130
of 255
Radiating Element – Open Waveguide or Hornor Horn
• Open waveguide (sometimes• Open waveguide (sometimes with a tapered horn section) is a good radiator but not often used in arrays because it is yphysically large and accordingly hard to arrange in a tight latticeIt i l t h f i b• It is also too heavy for airborne and space applications
• It has utility in thinned arrays where its directivity will help
• 8.2 – 12.4 GHzwhere its directivity will help control grating lobes
• Element spacing is ~1.5λpart of the solution is the
• λ = 3.6 – 2.4 cm• 15° beamwidth• Gain 17.4 – 20.3 dB– part of the solution is the
element gain which is small at the grating lobe location
• a=6.15 cm• b=4.25 cm• c=3.15 cmc 3.15 cm
SCF01 Electronic Scanned Array DesignSlide 131
of 255
Horn feeds
• SAR-Lupe – Single feed horn – no
electronic scanningelectronic scanning
• TecSAR– Eight feed horns at focus of g t eed o s at ocus o
reflector– Scan by switching feed
SCF01 Electronic Scanned Array Design
Figure 4 from Sharav, et al (© IEEE)Slide 132
of 255
Slotted Waveguideg
W id i l l d b i t t d ith• Waveguide is very low loss and can be integrated with a radiating element– Slots in waveguide allow RF to escapeSlots in waveguide allow RF to escape– Size and orientation of slot can be tailored for desired properties
• Corporate Fed– No phase variation with frequency to limit bandwidth
• Series feedFeed from one end introduces frequency scanning of beam– Feed from one end introduces frequency scanning of beam
• Center feed– Two back-to-back center feeds maintain boresight pointing until g p g
beams diverge– Used by RadarSat and Terra-SAR X
SCF01 Electronic Scanned Array DesignSlide 133
of 255
Radiating Element – Slotted WaveguideWaveguide
• Slotted waveguides are readily combined with waveguide basedwaveguide based corporate feed to provide low-loss RF distribution to 100’s of radiating slots
• Very wide band• But not electronically
scanned
SCF01 Electronic Scanned Array DesignSlide 134
of 255
Approachpp
• Slots are duals of dipoles• Easy to machine at high precision• Polarization depends on slot orientation• Feed is integral to waveguide
– Slots separated by one wavelength (or alternating slots at one-half wavelength ) create broadside beam
– Frequency scanning is inherentFrequency scanning is inherent– May be centerfed to avoid frequency scanning but beamwidth
increases away from nominal frequency
• Waveguide is low loss, light weight and inexpensive– Very popular for non-scanning arrays
SCF01 Electronic Scanned Array DesignSlide 135
of 255
Dual Polarized Approach for TerraSAR-XX
• Non inclined narrow wall slots in one• Non-inclined narrow wall slots in one waveguide generate the horizontal polarisation. The slots have to extend into the neighbouring broad walls of the waveguide to bewalls of the waveguide to be resonant. The edge slots in the narrow wall need to be excited with a pair of wires inside the waveguide and not by slot tilt in order forand not by slot tilt in order for minimum cross polarisation generation.
• Offset broad wall slots in the second waveguide generate the verticalwaveguide generate the vertical polarisation. In order to minimise the waveguide width using longitudinal, broad wall slots, ridge loading is used Both of the above slot typesused. Both of the above slot types exhibit pure polarisation generation and high isolation between the ports within a subarray.
SCF01 Electronic Scanned Array DesignSlide 136
of 255
Return Loss Bandwidth
• VSWR < 1.5 or ~ -15 dB S11VSWR 1.5 or 15 dB S11– Horizontal polarization bandwidth > 120 MHz– Vertical polarization bandwidth > 400 MHz
SCF01 Electronic Scanned Array Design
Figure 2 from Derneryd et al (© IEEE)Slide 137
of 255
TerraSAR-X Next Generation
• European Patent EP2100348S ti i• Serpentine inner conductor alters propagation velocity sopropagation velocity so that slots are excited in phase
• Propagation modes are not dispersive which broadens bandwidth
SCF01 Electronic Scanned Array DesignSlide 138
of 255
Return Loss Much Improved
• VSWR < 1.5 or ~ -15 dB S11H i t l l i ti• Horizontal polarization bandwidth > 650 MHz
• Vertical polarization• Vertical polarization bandwidth > 700 MHz
SCF01 Electronic Scanned Array DesignSlide 139
of 255
Radiating Element is Key to PerformancePerformance
• Impedance match, power transfer• Radiation resistance, scattering• Surface waves• Load impedance• Single element• Adjacent element (function of separation)• Scattering in receive• Q (quality factor) – energy storage
SCF01 Electronic Scanned Array DesignSlide 140
of 255
Radiating Element – Dipole (1)g p ( )
• Infinitesimal dipole has a cosine theta beam pattern – however infinitesimal dipoles are very inefficient
• Quarter wave dipoles have a moreQuarter wave dipoles have a more complicated beam pattern (not much different from a cosine theta pattern) –and are very efficientVertical polarization – complete azimuth coverage
1
1.5
2
30
60
90
120
150
Maximum gain is 1.647 or 2.2 dB
0.5
180 0
210
240
270
300
330
SCF01 Electronic Scanned Array Design
270
Three dimensional pattern (gain) representation Pattern cut through vertical plane Slide 141of 255
Coupled Dipole Arraysp p y
• Wideband Phased Array Antenna and Associated MethodsMethods– US Patent 6,512,487
(2003)
• This array approximates ideal current sheet– Potentially very broad band
and well matched
SCF01 Electronic Scanned Array DesignSlide 142
of 255
Radiating Element – Flared notchg
Fl d t h h th b t• Flared notch has the best performance for airborne applications– Very wide band– Near perfect aperture match
• Difficult arises in fabrication• Difficult arises in fabrication and assembly– Radiator stands off the array
faceface– Right angle interconnect
from t/r module to radiating elementelement
• Use only where benefits warrant added cost
SCF01 Electronic Scanned Array DesignSlide 143
of 255
SKA Alternative
• Crossed flared notch elements provide dual polarization for up to 10:1polarization for up to 10:1 bandwidth
• Scan performance is ±45°Scan performance is ±45• Radiating element match
is goods good
SCF01 Electronic Scanned Array DesignSlide 144
of 255
Patches
• Used by– Iridium
JPL L band designs– JPL L-band designs– Cosmo-Skymed– SEOSAR/PAZ
• Well suited to integration with array
SCF01 Electronic Scanned Array DesignSlide 145
of 255
Radiating Element – Patch (1)g ( )
• Patch•radiating•elements•offer•d b l f t dgood•balance•of•cost•and•
performance• Planar•configuration•lends•
itself to large areasitself•to•large•areas• Possible•to•mount•electronic•
components•on•the•back•for•higher level integrationhigher•level•integration
SCF01 Electronic Scanned Array DesignIllustrations•from•Byström•(©•Ericsson•Microwave•Systems) Slide 146
of 255
Radiating Element – Patch (2)g ( )
E-plane H-plane• These plots present S11 (return loss) as a function of scan angle• S11 is a measure of power reflected back to the source
– This power is not radiated• The radiating element is has little intrinsic loss
SCF01 Electronic Scanned Array Design
g– Allows computation of scan patterns on next page
Illustrations from Byström (© Ericsson Microwave Systems) Slide 147of 255
Radiating Element – Patch (3)g ( )
H Pl SE-Plane Scan
(1.00)
0.00
H-Plane Scan
(2.00)
(1.00)
0.00
(4 00)
(3.00)
(2.00)
Gai
n
(5.00)
(4.00)
(3.00)
Gai
n
1.00 1.25 1.50 1.75 2 00
(6.00)
(5.00)
(4.00)
(60) (40) (20) 0 20 40 60
1.00 1.25 1.50 1.75 2.00
(6.00)(60) (40) (20) 0 20 40 60
Scan Angle
2.00
( ) ( ) ( )
Scan Angle
• Element has good predicted performance across octave bandwidth• Need to do sensitivity analysis to material properties and manufacturingNeed to do sensitivity analysis to material properties and manufacturing
tolerances• Very important to validate predictions with test articles
SCF01 Electronic Scanned Array DesignSlide 148
of 255
T/R Modules
SCF01 Electronic Scanned Array DesignSlide 149
of 255
Transmit/Receive Modules
• T/R modules provide distributed gain and phase control, typically at each radiating element
They provide the flexibility enabling the attractive performance of– They provide the flexibility enabling the attractive performance of the ESA
• The cost of T/R modules has been the most important prestriction on their wide use
• Since the 1990’s, costs have declined precipitously yleading to the vast increase in ESA applications– Primarily because of commercial demand for MMICs, ASICs, etc
SCF01 Electronic Scanned Array DesignSlide 150
of 255
Two Types of Transmit / Receive ModulesModules
T/R module
T/R moduleT/R module
T/R moduleT/R module
T/R moduleT/R module
old
T/R module
T/R module
T/R module
dT/R module
T/R module
T/R module
T/R module
T/R module
T/R module
T/R module
T/R module
T/R module
T/R module
T/R module
T/R module
T/R module
T/R module
man
ifo T/R module
T/R module
T/R moduleman
ifold T/R module
T/R module
T/R module
T/R moduleman
ifold T/R module
T/R module
T/R module
man
ifold T/R module
T/R module
T/R moduleanifo
ld
T/R module
T/R module
T/R module
T/R d lT/R module
T/R module
T/R module
T/R module
T/R module
T/R module
T/R module
T/R module
T/R module
T/R module
m
T/R module
T/R module
T/R module
ma T/R module
T/R module
T/R module
T/R d lT/R module
T/R module
T/R moduleT/R module
T/R moduleT/R module
T/R module
T/R module
T/R module
T/R module
SCF01 Electronic Scanned Array Design• Tile (or Panel)• Brick Slide 151of 255
Northrop-Grumman’s History of TR ModulesModules
SCF01 Electronic Scanned Array Design
Illustration from R. Hendrix (© IEEE)Slide 152
of 255
Hughes T/R Module from High Density Microwave Packaging (HDMP) ProgramHigh Density Microwave Packaging (HDMP) Program
SCF01 Electronic Scanned Array Design
Illustration from George Stimson (© SciTech Publishing, Inc)Slide 153
of 255
Raytheon T/R Module for THAADy
SCF01 Electronic Scanned Array Design
Left image and upper right image from Kopp (© IEEE)Lower right image © Raytheon Slide 154
of 255
Monolithic Microwave Integrated Circuits (MMIC)Are a Fundamental Enabler for T/R ModulesAre a Fundamental Enabler for T/R Modules
MMIC f d t l bl f t/ d l d h• MMICs are a fundamental enabler of t/r modules and hence ESAs
• At X-band, GaAs is the semiconductor material of choice. ,Processing geometries are 0.25μ (micrometers) or less. Facility capitalization is very expensive so the price of these components includes significant amortization making theircomponents includes significant amortization, making their price very sensitive to volume.
• With the advent of cell phones, production volume picked up nicelnicely.
• Most t/r modules are made by system houses and most of these utilize in-house foundries. The system houses regard y gthese capabilities as competitive discriminators and highly proprietary; accordingly they do not sell outside.
SCF01 Electronic Scanned Array DesignSlide 155
of 255
M/A-Com Commercial Chip Set for T/R ModulesModules
• The M/A-Com foundry in Roanoke, VA is one of the few independent sourcesfew independent sources of chips for t/r modules.
• Their chip set providesTheir chip set provides good performance.
SCF01 Electronic Scanned Array Design
Image © MA-ComSlide 156
of 255
Example of Module Efficiency (M/A-Com chip set)Com chip set)
• Using typical current consumption from manufacturer’s specification
Part Type Part Number IDD (A) Voltage PowerDuty
FactorAve
PowerLNA MA01503D 0.19 5 0.95 90% 0.855CLC MA03503D 0.325 5 1.625 100% 1.625Driver MAAPGM0034 0.2 10 2 10% 0.2PA MA08509D 3.9 10 39 10% 3.9
Total 6.58
10 watts peak power, 10% transmit duty RF Out 1
Efficiency 15%y
SCF01 Electronic Scanned Array Design
Important omissions:DC-DC converter efficiencyPA Drain switch voltage drop Slide 157
of 255
MMIC Die Sizes
Description Part Number Length mm
Width mm
Height mm
Area mm2
LNA MA01503D 4.58 3.08 0.125 14.11
Gain/Phase C t l
MA03503D 5.98 3.97 0.075 23.76ControlPA Amp MA08509D 4.58 4.58 0.075 20.98
D i A MAAPGM0034 2 48 1 58 0 075 3 92Driver Amp MAAPGM0034 2.48 1.58 0.075 3.92
62.76
SCF01 Electronic Scanned Array DesignSlide 158
of 255
Phase Shifters & Time Delay Unitsy
• Switched– Switched lines (TDU)
Reflection
• Analog– Ferrite phase shifters
U d i ld t– Reflection– Loaded line– Hi-Lo pass filters
• Used in older systems designed before microwave integratedp
• Lowest cost, better in most performance
microwave integrated circuit revolution
aspects– Cannot handle high power
SCF01 Electronic Scanned Array DesignSlide 159
of 255
Time Delay Units
• Coaxial cable is an obvious choice– 1000 feet is 31 pounds and $48.00– Loss is 1 dB per 10 foot– Loss is 1 dB per 10 foot
• For L= 1 meter, H=1 meter, azimuth and elevation = 60° and λ= 3 cmλ= 3 cm
• We need 272 meters of cable or about 900 feet for two-dimensional time delay steeringtime delay steering
• Printed circuits are better
SCF01 Electronic Scanned Array Design
(L2 " sinazimuth "H2 " sin elevation)/62 = (Area2 " sinazimuth " sin elevation)/62
Slide 160of 255
TELA TDU Module
SCF01 Electronic Scanned Array DesignSlide 161
of 255
High-pass / Low pass Phase Shifterg p p
G f th fi t t ti th t hi h d l filt h d diff t• Garver was one of the first to notice that high-pass and low-pass filters had different phase shifts that maintained a constant difference for an appreciable bandwidth.
• At microwave frequencies the lumped-element values are both realizable and small and very importantly compatible with MMIC devices and processingand very importantly compatible with MMIC devices and processing
Pi and Tee are equivalent and may be selected according to whichever is more convenientaccording to whichever is more convenient
SCF01 Electronic Scanned Array DesignPresentation follows Robert V. Garver’s 1972 paper
Slide 162of 255
Tee Filter Analysisy
• ABCD formulation for cascaded lumped elements5V1
6 5A B
6 5V2
65I1
6=
5C D
6 5I2
6
• The representation for a Tee filter is one series, one shunt and one series component ----A B
C D
----N
=
---- 1 ! BNXN j(2XN ! BNX2N)
jBN 1 !BNXN
----- -N
- -
SCF01 Electronic Scanned Array DesignSlide 163
of 255
Transmission Characteristic
• Accordingly the transmission term (S21) is
S21 =2
• Or
S21A + B + C + D
S21 =2
2 (1 ! BNXN) + j (BN + 2XN !BnXN2)
• And the transmission phase characteristic is
( N N) j ( N N n N )
? = tan!1
5!
BN + 2XN ! BNXN2
2 (1 ! BNXN)
6SCF01 Electronic Scanned Array Design
52 (1 BNXN)
6Slide 164
of 255
High Pass Filter Analysisg y
• The high pass filter exchanges the series and shunt circuit elements and provides an equal phase shift with the opposite signthe opposite sign
• The net phase shift difference between the two circuit paths ispaths is
"? = 2 tan!1
5!
BN + 2XN ! BNXN2
2 (1 B X )
6?
52 (1 !BNXN )
6
SCF01 Electronic Scanned Array DesignSlide 165
of 255
Input and Output Matchingp p g
E h i it i t h d if• Each circuit is matched if
|S21| = 1 |S11| =q
1 ! |S21|2
• Under these conditions
q
BN =2XN
XN2 + 1
XN = tan
3"?
4
4• However, an exact match is possible at only one
frequency• Frequency variation of insertion phase and match is not
extreme enabling octave bandwidths
SCF01 Electronic Scanned Array DesignSlide 166
of 255
Impedance Match Conditionsp
Low Pass Tee filter2.0
(Xn)
Low Pass Tee filter
11.2522.530
1.0
eact
ance
( 456090120150
0.5
Ser
ies
Re 150
180
0.2
orm
aliz
ed
- 0.5 - 1.0 - 2.0 - 5.0 -10.00.1 ρ=1.1 ρ=1.0 ρ=1.1
Normalized Shunt Reactance (B )
N
Normalized Shunt Reactance (Bn)
SCF01 Electronic Scanned Array DesignSlide 167
of 255
Insertion Loss
Phase Shifter Loss
-0.1
0Phase Shifter Loss
11.2522.545
-0 4
-0.3
-0.2
)
90180
-0.6
-0.5
0.4
|S21
| (dB
-0.8
-0.7
0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6-1
-0.9
ω / ω0
ω / ω0
SCF01 Electronic Scanned Array DesignSlide 168
of 255
Phase Shifter Return Loss
Phase Shifter Match
-5
0Phase Shifter Match
11.2522.545
-15
-10
)
90180
-25
-20
|S11
| (dB
-35
-30
0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6-40
-35
ω / ω0
ω / ω0
SCF01 Electronic Scanned Array DesignSlide 169
of 255
Phase Accuracy over Frequencyy q y
Frequency Dependence of Phase Shift
180 -20
dB
-20
dB
-25
dB
-25
dB
-30
dB
-30
dB
Return Loss
Frequency Dependence of Phase Shift
11.2522.545
90
180
t (°)
90180
45
Pha
se S
hift
11.25
22.5P
0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6
Diamonds represent 2° error
ω / ω0
ω / ω0
SCF01 Electronic Scanned Array DesignSlide 170
of 255
Benefits and Limitations
• High-pass / Low-pass phase shifters are widely used because of their combination of performance and simplicitysimplicity– Easily fabricated and integrated in MMIC process
• Two sources of bandwidth limitationTwo sources of bandwidth limitation – Beam squint– Phase shifter error– Limitation is acceptable for most applications
SCF01 Electronic Scanned Array DesignSlide 171
of 255
Packagingg g
• Tight lattice spacing results in component packaging challengesB i k t l d l id t t l d• Brick style modules provide greatest volume and some integration challenges
• Tile style modules are preferred and achievable• Tile style modules are preferred and achievable
SCF01 Electronic Scanned Array DesignSlide 172
of 255
Georgia Tech 64-Element Antennag
• Liquid Crystal Polymer substrateP t h di ti l t• Patch radiating elements
• SiGe BiCMOS T/R modulesmodules– 7 dB gain– 3-bit phase shifter3 bit phase shifter– 500 MHz bandwidth– Noise figure ~2.5 dB
SCF01 Electronic Scanned Array DesignSlide 173
of 255
7-21 GHz Dual-Polarized Arrayy
SCF01 Electronic Scanned Array DesignSlide 174
of 255
Thermal Dissipation Constrains DesignsDesigns
ESA l f h• ESAs generate a lot of heat• Ground based ESAs eventually must transfer heat into air
– Problem in the desertProblem in the desert• Airborne ESAs are liquid cooled with tight temperature control
– Lots of chilled airflow• Spaceborne ESAs must radiate heat, directly or transferred to
dedicated thermal radiators– Direct radiation is far simpler, lighter and more reliability but imposesDirect radiation is far simpler, lighter and more reliability but imposes
limit on RF power density• High operating temperatures shorten component lifetime, reduce
amplifier gain increase noise figureamplifier gain, increase noise figure
SCF01 Electronic Scanned Array DesignSlide 175
of 255
Technology Base and Cost
SCF01 Electronic Scanned Array DesignSlide 176
of 255
DARPA and Military Manufacturing Technology Programs Initiated the Technology BasePrograms Initiated the Technology Base
• DARPA - Very High Speed Integrated Circuit (VHSIC)– Industry teams
DARPA Mi M lithi I t t d Ci it• DARPA - Microwave Monolithic Integrated Circuit (MMIC)– Industry teams– Industry teams
• USAF - T/R Module Manufacturing Technology (1989-1992)99 )– Westinghouse-Texas Instruments Team– Hughes Aircraft Company
SCF01 Electronic Scanned Array DesignSlide 177
of 255
Consumer Products Provided Final Cost ReductionsCost Reductions
• Personal Computers, Mobile Phones and Wireless Networking dwarfed government investment starting in the 1990’sthe 1990 s
SCF01 Electronic Scanned Array DesignSlide 178
of 255
AESA Supplierspp
US• US• Northrop Grumman Electronic Systems (formerly Westinghouse)• Raytheon Systems (formerly Raytheon, Texas Instruments and Hughes)
/• Harris / Texas Instruments• Lockheed Martin (formerly Martin (formerly General Electric (formerly
General Electric and RCA)))ITT Gilfillan• ITT-Gilfillan
• Europe• EADS
A t i (L b d d l )• Astrium (L-band space modules)• EADS Deutschland GmbH, Ulm (SMTR used in TerraSAR-X & CAESAR)
• Defense and Security (MEADS modules)• ThalesThales
• Aerospace Division (Elancourt and Crawley) RBE2 AESA for RAFALE• Thales Alenia Space Italia (for Cosmo-Skymed)
• ALCATEL ESPACE, Toulouse, FRANCE( ENVISAT and Radarsat), , ( )
SCF01 Electronic Scanned Array DesignSlide 179
of 255
Gallium Arsenide
• US• All of the above plus
M/A Com (acquired by Cobham plc Dorset England in• M/A-Com (acquired by Cobham plc Dorset, England in September 2008)
• TriQuint (formerly Texas Instruments)
• Europe• United Monolithic Semiconductors (UMS), a Franco-German
i d b EADS d Th lenterprise owned by EADS and Thales• e2v (formerly English Electric Valve)
• Asian• Asian• Offshore (Win Semiconductor, …)
SCF01 Electronic Scanned Array DesignSlide 180
of 255
T/R module cost has been reduced by orders of magnitude since 1980orders of magnitude since 1980
• Actual numbers are very hard to determine being proprietary, competition sensitive and occasionally embarrassingembarrassing
SCF01 Electronic Scanned Array DesignSlide 181
of 255
Congressional Budget Office Opiniong g p
P t i C t f G A MMIC Si f T/R M d l
• Chipset on described on slides 175-177 totals 63 mm2
Parametric Cost of GaAs MMICs Size of a T/R Module
• GaAs prices have declined because of WiFi & Mobile Phones
SCF01 Electronic Scanned Array DesignSlide 182
of 255
Naval Air Warfare Center BAA Goal
B d A A t f M f t i R h d• Broad Agency Announcement for Manufacturing Research and Development of X-Band Active Electronically Scanned Array Transmit/Receive Modules N68936-96-R-0282 dated July 15, 1996
• “The thrust of this effort is to create design and manufacturing innovations to achieve per element module cost of $300 after the first 20,000 modules production”
– Contract N68936-97-C-0013 for $3,554,246 awarded to Hughes Aircraft Company November 22, 1996
– Contract N68936-97-C-0017 for $4,498,223 awarded to Raytheon Electronic Systems December 17 1996Systems December 17, 1996
SCF01 Electronic Scanned Array DesignSlide 183
of 255
ESA Fed reflectors conceived as a solutionto the high cost of T/R Modulesto the high cost of T/R Modules
I 1982 R b M ill l d ESA f d fl ( hi h h• In 1982, Robert Mailloux analyzed ESA fed reflectors (which he called hybrid antennas) in The Handbook of Antenna Design– “Hybrid antennas would be unnecessary if phased arrays could be y y p y
made very inexpensively. If the system designers’ dream of a low-cost array with thousands of little elements, each costing a few dollars and controlled by some central processor had happened or would soon happen, there would be little need to expend much time or effort in the development of hybrid antennas.” Includes not just
•T/R module functionT/R module functionBut also•Frequency synthesizer•Receiver•User Interface•Power Supply
SCF01 Electronic Scanned Array Design
Mailloux, R. J., “Hybrid Antennas,” Ch. 5 in The Handbook of Antenna Design, Vol. 1, A. W. Rudge, Milne, Olver, Knight, eds., Peter Peregrinus, London, 1982. Slide 184
of 255
USA Prices
$• Feb 16, 2007 – Raytheon has been awarded a $212 million contract by the Missile Defense Agency for the manufacture, delivery and integration support of one Terminal High Altitudedelivery and integration support of one Terminal High Altitude Area Defense radar, also called the AN/TPY-2 radar. – Radar contains 25,344 modules – puts a ceiling of $8,365 for each
d l i (if thi l id d t t)module price (if everything else was provided at no cost)
Clearly, T/R module cost is < $1,000 each
SCF01 Electronic Scanned Array Design
y, $ ,
Slide 185of 255
European Pricesp
• Within the framework of the MEADS design and development programme, EADS Defense & Security Defence Electronics had been awarded a contract worthDefence Electronics had been awarded a contract worth about €120 million for the production of approx. 40,000 T/R modules and associated electronic components p(€3,000 each)– First 5,000 modules delivered in 2008
SCF01 Electronic Scanned Array DesignSlide 186
of 255
PART FOURPART FOUR
SCF01 Electronic Scanned Array DesignSlide 187
of 255
ESA Examples
SCF01 Electronic Scanned Array DesignSlide 188
of 255
Airborne ESA Systemsy
Northrop Grumman/Raytheon AN/APG-77 F-22 RaptorNorthrop Grumman/Raytheon AN/APG 77 F 22 Raptor Northrop Grumman AN/APG-80 F-16E/F Block 60 Fighting Falcon Northrop Grumman AN/APG-81 F-35 Joint Strike Fighter Northrop Grumman Multi-role AESA Boeing Wedgetail (AEW&C) Northrop Grumman APY-9 E-2D Advanced Hawkeye Raytheon AN/APG-63(V)2 F-15C Eagle y ( ) gRaytheon AN/APG-79 F/A-18E/F Super Hornet Raytheon AN/APQ-181 B-2 Spirit bomberEuropean GTDAR (GEC-Thomson-DASA Airborne Radar) consortium, now BAE Systems, Thales, and EADS
AMSAR (Airborne Multirole Solid State Active Array Radar ) Eurofighter and Rafale fighter Radar y y ) g g
Captor-E CAESAR (CAPTOR Active Electronically Scanning Array Radar) Eurofighter Typhoon
ThalesRBE2-AA (Radar à Balayage Electronique 2)
SELEX Sensors and Airborne Systems S.p.A. created by the merger of the avionics businesses of Finmeccanica and part of BAE Systems
Seaspray 7000EVixen 500E for helicopters
Mitsubishi Electric Corporation J/APG-1 Mitsubishi F-2 fighter Ericsson Erieye AEW&C and NORA AESA JAS 39 Gripen Phazotron-NIIR Zhuk-AE (FGA-29 / FGA-35 ) MiG-35 Tikhomirov NIIP Epaulet-A (or Epolet-A)Elta EL/M-2083 aerostat-mounted air search radar Elta EL/M-2052 for fighters
Elt EL/M 2075 d f th IAI Ph l AEW&C tElta EL/M-2075 radar for the IAI Phalcon AEW&C system
SCF01 Electronic Scanned Array DesignSlide 189
of 255
Ground and Naval ESA Systemsy
l i f i d i fThales APAR
multi-function radar, primary sensor of Dutch De Zeven Provinciën and German Sachsen class frigates
SELEX Sensors and Airborne Systems S.p.A. created by the merger of the avionics businesses of Finmeccanica
EMPAR (European Multifunction Phased Array Radar)avionics businesses of Finmeccanica
and part of BAE SystemsArray Radar)
Elta EL/M-2080 Green Pine ground-based early warning AESA radar
Elta EL/M-2248 MF-STAR multifunction naval radar
U S DD(X) CG(X) d CVN 21Raytheon AN/SPY-3 U.S. DD(X), CG(X) and CVN-21 next-generation surface vessels
Raytheon U.S. National Missile Defense X-Band Radar (XBR)
MEADS International (MI), MBDA Italia, Lenkflugkörpersysteme (LFK) in Multifunction Fire Control Radar (MFCR)Lenkflugkörpersysteme (LFK) in Germany and Lockheed Martin
Multifunction Fire Control Radar (MFCR)
Lockheed Martin Space Systems Company (Raytheon) THAAD system fire control radar
BAE SAMPSON Insyte multi-function radar for UK. Type 45 destroyers
Mi bi hi El i C i (M l ) FCS 3Mitsubishi Electric Corporation (Melco) FCS-3
Mitsubishi Electric Corporation OPS-24 (The world's first Naval Active Electronically Scanned Array radar) FPS-5 Japanese ground-based next generation Missile Defense Radar
CEA Technologies CEAFAR Naval Phased ArrayCEA Technologies CEAFAR Naval Phased Array
SCF01 Electronic Scanned Array DesignSlide 190
of 255
Most Radio Telescopes are Reflectorsp
Arecibo is 305 meters diameter (73,000 m2) spherical dish (fixed position)Photo courtesy of the NAIC - Arecibo Observatory, a facility of the NSF
Lovell Telescope is the third largest steerable radio telescope in the world © Credit: Jodrell Bank Centre for Astrophysics, University of Manchester
SCF01 Electronic Scanned Array DesignHaystack is 37 meters diameter (1,075 m2) (re-positionable)© MIT
Proposed Square Kilometer Array (SKA) will be some form of ESAPhoto © Copyright CSIRO (Commonwealth Scientific and Industrial Research Organisation)
Slide 191of 255
THAAD
F X b dFrequency X-bandArray size (m2) 9.2T/R Modules 25 344T/R Modules 25,344Subarrays (Tx/Rx) 72/72Scan (Az/El) 53°/53°Mechanical El 10° - 60°
SCF01 Electronic Scanned Array DesignSlide 192
of 255
SCF01 Electronic Scanned Array DesignSlide 193
of 255
Airborne Fighter Aircraft have Transitioned to Active ESATransitioned to Active ESA
• F-15 Example
• 18 F-15C aircraft retrofitted with ESA radar entered service in 2000E h d f• Enhanced performanceand improved maintainability
SCF01 Electronic Scanned Array Design
Images © Boeing CorporationSlide 194
of 255
ESAs in Space
SCF01 Electronic Scanned Array DesignSlide 195
of 255
Iridium Communications Satellite
66 t llit t ll ti• 66 satellite constellation– 5 May 1997 to
7 May 1998 (72)y ( )• Altitude 781 km• Inclination 86.4°• Frequency 1.62 GHz• Antenna boresight 50°
f difrom nadir• Antenna size 0.86m x
1 88 mIridium Prototype Installed at Smithsonian Museum 1.88 m– 106 patch radiators
• 8 x 16 Butler Matrix Feed
yp
SCF01 Electronic Scanned Array DesignSlide 196
of 255
Iridium Beams in U-V Spacep
SCF01 Electronic Scanned Array DesignSlide 197
of 255
Iridium Beams on Globe
SCF01 Electronic Scanned Array DesignSlide 198
of 255
Iridium Beam on Globe (detail)( )
SCF01 Electronic Scanned Array DesignSlide 199
of 255
Iridium Beams projected to Groundp j
SCF01 Electronic Scanned Array DesignSlide 200
of 255
Some Radars On-Orbit
S ti l C b d T SAR X G X b dSentinel – C-band© European Space Agency
TerraSAR-X – Germany X-band© Astrium GmbH
SCF01 Electronic Scanned Array DesignCosmo-SkyMed – Italy X-band© Finmeccanica
RadarSat-2 – Canada C-band© Canadian Space Agency
Slide 201of 255
On-orbit and Planned Radar Satellites
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
USA SeaSAT / SIR / SRTM L/C/X bands
Japan JERS-1, ALOS, ALOS-2 L-band
Argentina SAOCOM L-band
w
USA-India NISAR L/S-band
Germany-Japan TanDEM-L (2023) L-band
UK NovaSAR S-band
Tim
e N
ow
Commercial Urthecast S/X-band
Canada RadarSat-1,2 / RCM C-band
European Space Agency ERS-1,2 / EnviSat / Sentinel C-band
Germany-military SAR-Lupe / SARah X-band
Germany-civilian TerraSAR-X, TanDEM-X, TerraSAR-NG, HRWS (2022) X-band
Italy Cosmo-Skymed, CSG X-bandy y
Israel TecSAR X-band
India RISAT-2 / RISAT-1 X/C bands
Korea Kompsat-5, 6 X-bandESAplanar arrayreflector
SCF01 Electronic Scanned Array DesignSlide 202
of 255
p
Spain PAZ X-band
S
Some Private Enterprise Plansp
• Iceye– Constellation of six microsatellites with Synthetic Aperture Radar
(SAR) imaging with first launch end of 2017(SAR) imaging with first launch end of 2017– Build own satellites
• UrtheCast– Plan eight SAR satellite constellation launched in 2019 and 2020– Supplier is Surrey Satellite dual band (X and L) based on
N SARNovaSAR
• XpressSARConstellation of four satellites planned to launch beginning in– Constellation of four satellites planned to launch beginning in 2020
– Satellite supplier unnamed
SCF01 Electronic Scanned Array DesignSlide 203
of 255
Comparative Radar Satellite PerformancePerformance
60P⋅G=70 (dBW)
P⋅G2=120 (dBW)
P⋅G2=130 (dBW)
40
50
P⋅G=60 (dBW)
2
P⋅G2=100 (dBW)
P⋅G2=110 (dBW)
S C/
DESDynI
RADARSAT
ERSENVISAT Sentinel
SAR-Lupe
TerraSAR-X
COSMO-SkyMedTecSAR
n (d
B)
30
40P⋅G=50 (dBW)
P⋅G2=70 (dBW)
P⋅G2=80 (dBW)
P⋅G2=90 (dBW)SEASATSIR-ASIR-B
SIR-C/LJERS-1 ALOSALOS-2
mum
Gai
20
P⋅G=40 (dBW)
P⋅G2=50 (dBW)
P⋅G2=60 (dBW)
( )
Max
im
10 20 3010
P⋅G=30 (dBW)P⋅G2=40 (dBW)
100 W 1000 W
Average Transmit Power (dBW)Average Transmit Power (dBW)
SCF01 Electronic Scanned Array DesignSlide 204
of 255
Satellite ESAs Optimized for SARp
Satellite# of
Modules Dx ( ) Dy ( )Azimuth
LimitElevation
LimitALOS 80 9.42 0.61 3.0° 54°
ALOS-2 180 4.19 0.68 6.8° 47°
RADARSAT 512 16.56 0.83 1.7° 37°
Envisat 320 17.77 0.72 1.6° 44°
Sentinel 280H/280V 15.83 0.74 1.8° 43°
Cosmo-Skymed 1280 9 17 0 70 3 1° 45°Cosmo Skymed 1280 9.17 0.70 3.1 45
Cosmo NG 2560
TerraSAR-X 384 12.81 0.75 2.2° 42°
TerraSAR-NG 1,280 9.17 0.7 3.1° 45°
SCF01 Electronic Scanned Array Design• Az and El computed to exclude grating lobe
Slide 205of 255
ESA RF Power Densities
COSMO Sk M d d SEOSAR/PAZ t h di t th th• COSMO-SkyMed and SEOSAR/PAZ uses a patch radiator; the other satellites use waveguide which may have better thermal dissipation properties
Satellite Band (RF) Watts per m2
ALOS/PALSAR L-band 5
ALOS-2 L-band 12
RADARSAT C-band 13
ENVISAT C b d 25ENVISAT C-band 25
Copernicus (Sentinel) C-band 50
COSMO-SkyMed X-band 90y
SEOSAR/PAZ X-band 117
TerraSAR-X X-band 129
SCF01 Electronic Scanned Array DesignSlide 206
of 255
L/C/X Band Antenna(s)( )
SCF01 Electronic Scanned Array DesignImages courtesy NASA/JPL-CaltechSlide 207
of 255
TerraSAR-X
Dual polarized slotted waveguide radiator and module assembly
Spacecraft structure showing location of 12 antenna panels
Module assembly including polarization switching and FPGA controller
SCF01 Electronic Scanned Array Design
One of 12 antenna panels composed of 32 T/R module/radiator assemblies
6.3 watt (38 dBm) SMTR modulesImages © IEEESlide 208
of 255
TerraSAR-X NG
U d t d• Under study• Wider Bandwidth
600 MHz (WRC 2007)– 600 MHz (WRC 2007)– -1.2 GHz (WRC 2016)
• New Radiating Elementg– European Patent EP2100348– Serpentine inner conductor
alters propagation velocity soalters propagation velocity so that slots are excited in phasePropagation modes are not– Propagation modes are not dispersive which broadens bandwidth
SCF01 Electronic Scanned Array DesignSlide 209
of 255
Italy - COSMO-SkyMedy y
X b d• X-band• ESA Design• 5 7m x 1 4m array5.7m x 1.4m array• 1,900 kg• ~5 kW peak transmit• 1,280 TR modules
manufactured by Thales Alenia Space ItaliaAlenia Space Italia
• Incorporates true time delay– Up to 15 wavelengths
• Growth option to five phase centers (channels) for MTI
SCF01 Electronic Scanned Array Design
Images © e-GEOS S.p.A.Slide 210
of 255
COSMO-Skymed Satellite Radary
• Four satellite constellation• Four satellite constellation– 8 June 2007 to
5 November 2010• Altitude 619.6 km• Inclination 97.86°• Frequency 9.6 GHz• Antenna boresight 34° from g
nadir• Antenna size 5.7 m x 1.4 m
– 15,360 patch radiators (240x64)• Pulsewidth up to 100 μs• Duty Cycle Tx up to 30%• PRF up to 4.5 kHz• Beam steering
– Elevation ±20°– Azimuth ±2°
Beamwidth
Artist's rendition of a COSMO-SkyMed(image credit: ASI)
• Beamwidth– Azimuth 0.3°– Elevation 1.7° to 6°SCF01 Electronic Scanned Array Design
Slide 211of 255
Antenna Beams in U-V Spacep
SCF01 Electronic Scanned Array DesignSlide 212
of 255
Antenna Beams on Globe
SCF01 Electronic Scanned Array DesignSlide 213
of 255
Antenna Beams on Globe (detail)( )
SCF01 Electronic Scanned Array DesignSlide 214
of 255
Antenna Beams Projected to Ground
SCF01 Electronic Scanned Array DesignSlide 215
of 255
L-Band Trade Study
SCF01 Electronic Scanned Array DesignSlide 216
of 255
L-band Systemsy
• History– Shuttle (JPL)
JERS 1 (JAXA)– JERS-1 (JAXA)– ALOS (JAXA)– ALOS-2 (JAXA)( )– SAOCOM (CONAE)
• Planned/Proposed Systems– DESDynI NISAR (JPL+ISRO)
T SAR L (DLR/JAXA)– TerraSAR-L (DLR/JAXA)
SCF01 Electronic Scanned Array DesignSlide 217
of 255
Geometric Relationshipsp
• Angles and lengths easily computed with trigonometric identities
hρ
θlookθincident
trigonometric identitiesre
re
α
;2 = r2e + (re + h)2 ! 2re(re + h) cos(,); e ( e ) e( e ) ( )
sin(,)
;=
sin(3look)
r=
sin(: ! 3incident)
r + h
SCF01 Electronic Scanned Array DesignSlide 218
of 255
; re re + h
L-band Arraysy
10.0
9
6.5
9
2.9
0.9
ALOS-2
10.0
TanDEM-L Feed
13.5
3.5
3.5
SAOCOM DESDyni ESA
SCF01 Electronic Scanned Array DesignSlide 219
of 255
System Performancey
ALOS-2 SAOCOM DESDynI DESDynI NISAR TanDEM-L
Altitude 628 km 620 km 761 km 761 km 740 km 745 km
15 m 12 m 15 mAntenna Size 2.9 x 9.9 m 3.5 x 10 m 3.5 x 15 m 15 m diameter
12 m diameter
15 m diameter
Transmit Power 5 kW 3.9 kW 3.2 kW 3.2 kW 3.0 kW 10.9 kW
NESZ (spec) -24 ~ -28 dB
-24 ~ -28 dB -35 dB < -20 dB -20 ~ -25 dB
Resolution 1 ~ 100m 10~ 100m 3m ~ 100m 3 ~ 10m 1 ~ 10 m
Incidence Angle 8° to 70° 20° to 50° 30° to 50° 30° to 50° 34° to 48°
Swath Width 350 km 320 km 350 km 350 km > 200 km 350 km
Electronic Scan±30° elevation
±3.5° azimuth
±25° elevation
±40° azimuth
±9° elevation
no azimuth scan
±8° elevation
±2° azimuth
SCF01 Electronic Scanned Array DesignSlide 220
of 255
Antenna Characteristics
ALOS-2 SAOCOM DesDYNI DesDYNI NISAR TanDEM-L
Array Size 2.9 x 9.9m 3.5 x 10.0m 3.5 x 15.0 m 0.5 x 4.0 m 0.5 x 1.5 m 1.0 x 4.6 m
Reflector Diameter 15 m 12 m 15 mReflector Diameter 15 m 12 m 15 m
Number of Modules 180 140 1,600 64 24 192
Number of Phase C t (El) 18 20 20 32 12 32Centers (El) 18 20 20 32 12 32
Phase Center Spacing (El) 0.63 lambda 0.74 lambda 0.68 lambda 0.52 lambda 0.52 lambda 0.60 lambda
Number of Phase Centers (Az) 10 7 80 2 2 6
Phase Center Spacing (Az) 4.32 lambda 6.07 lambda 0.60 lambda 1.05 lambda 1.05 lambda 0.68 lambda
T/R Module Power 34 Watts 28 Watts 2 50 Watts 125 Watts 56.6 Watts
Peak Transmit Power 6.1 kW 3.9 kW 3.2 kW 3.2 kW 3.0 kW 10.9 kW
EIRP (PG) 66 dBW 75 dBW 76 dBW 66 dBW 68 dBW 71 dBW
PG2 114 dBW 114 dBW 116 dBW 97 dBW 100 dBW 100 dBWSCF01 Electronic Scanned Array Design
Slide 221of 255
Advanced Land Observing Satellite "DAICHI" (ALOS)DAICHI (ALOS)
• ALOS-2– L-band
ESA design– ESA design– 9.9m x 2.9m– 2,120 kg, g– 5 kW peak transmit power– 180 TR modules– 5.2kW (EOL) power system
Image © JAXA | Japan Aerospace Exploration Agency
SCF01 Electronic Scanned Array DesignSlide 222
of 255
ALOS (Advanced Land Observing Satellite)PALSAR (Phased Array Synthetic Aperture Radar)PALSAR (Phased Array Synthetic Aperture Radar)
PALSAR Electrical Model PALSAR-2 Flight Model
SCF01 Electronic Scanned Array Design
Images © JAXA | Japan Aerospace Exploration AgencySlide 223
of 255
ALOS-2 PALSAR Arrayy
Array Width = 9.90 metersArray Height = 2.90 metersArray Area = 25.84 square meters
Delta X = 0 165 meters (6 50 inches)
Wavelength = 0.229 metersNumber of Elements = 1080Areal Gain (4⋅π⋅A/λ2) = 37.9 dBiDelta X = 0.165 meters (6.50 inches)Delta Y = 0.145 meters (5.71 inches)Number of elements = 1080Triangular angle = 60 4 degreesTriangular angle 60.4 degreesColors denote subarrays
SCF01 Electronic Scanned Array DesignSlide 224
of 255
Used Uniform Element Factor
10
0
10 Maximum Gain = 7.6
-30
-20
-10
Gai
n (d
B)
-90 -75 -60 -45 -30 -15 0 15 30 45 60 75 90-50
-40
θ (°)
Phi=0°Phi=45°Phi=90°cos
θ (°)
• Aperture equal to lattice size• Compare to slide 13 of this presentation• Compare to slide 13 of this presentation
Slide 225of 255SCF01 Electronic Scanned Array Design
Antenna PatternBoresight and SteeredBoresight and Steered
SCF01 Electronic Scanned Array DesignSlide 226
of 255
Azimuth CutSteered in AzimuthSteered in Azimuth
40
30→ ← 3 dB Beamwidth = 6.1°
→ ← 10 dB Beamwidth = 10.5°
20
→ ←
10
Gai
n (d
B)
0
-10
Maximum Gain = 36.4θ = 5.0°,φ = 0.0°
Array FactorSubarray FactorArray Factor Grating LobesSubarray Factor Nuls
SCF01 Electronic Scanned Array DesignSlide 227
of 255
-90 -75 -60 -45 -30 -15 0 15 30 45 60 75 90-20
Azimuth (degrees)
φ
Elevation CutSteered in ElevationSteered in Elevation
40
30→ ← 3 dB Beamwidth = 5.7°
→ ← 10 dB Beamwidth = 9.6°
20
10
Gai
n (d
B)
0
-10
Maximum Gain = 36.7θ = 40.0°,φ = 90.0°
Array FactorSubarray Factor
SCF01 Electronic Scanned Array DesignSlide 228
of 255
-90 -75 -60 -45 -30 -15 0 15 30 45 60 75 90-20
Elevation (degrees)
ESA Beamwidth Fairly Constant with ScanScan
5
6
7 Azimuth BeamwidthElevation Beamwidth
5
6
7 Azimuth BeamwidthElevation Beamwidth
3
4
Bea
mw
idth
( °)
3
4
Bea
mw
idth
( °)
0 1 2 3 4 50
1
2
A i th S (°)
0 10 20 30 40
0
1
2
El ti S (°)
• Elevation and Azimuth beamwidth change with cos-1 θ
Azimuth Scan (°) Elevation Scan (°)
SCF01 Electronic Scanned Array DesignSlide 229
of 255
ALOS-2 Gain as a Function of Scan
40
39
Azimuth ScanElevation Scancos θ
38
37
Gai
n (d
B)
36
0 10 20 30 4035
SCF01 Electronic Scanned Array DesignSlide 230
of 255
0 10 20 30 40Scan Angle (°)
Beam Laydowny
• Elevation scan covers nadir to 20°grazing (70° incidence) angle• Individual beam includes Doppler of ±2 5 kHzIndividual beam includes Doppler of ±2.5 kHz
SCF01 Electronic Scanned Array DesignSlide 231
of 255
Additional Features
• Split aperture to form two beams on receive• Reduce aperture width from five to three panels to
b d b i i thbroaden beam in azimuth
SCF01 Electronic Scanned Array DesignSlide 232
of 255
OFFSET REFLECTOR
SCF01 Electronic Scanned Array DesignSlide 233
of 255
Radar Satellite Geometry & Timingy g
Radar600 Radar altitude = 619 6 km
tude
(km
)
200300400500600
1314151617181920
Radar altitude = 619.6 km-3 dB swath from 421 km to 440 km
-15 dB swath from 396 km to 467 kmPulse repetition frequency = 3.00 kHz
Transmit pulse width = 33 μ secTransmit duty cycle = 10%
877
636
430
261
20
4
Alti
t
0 5001000
0100200
Horizon60°50°38°25°20°
345678910111213 Transmit duty cycle = 10%Time = 10,000 μ sec
8
Ground offset Distance (km)
10001500
2000
2
2704
rriva
l (°)
2500
5101520
-15 dB
0000 10 10 10 1 20 1 20 1 2 30 1 2 30 1 2 30 1 2 3 40 1 2 3 40 1 2 3 40 1 2 3 4 50 1 2 3 4 50 1 2 3 4 5 60 1 2 3 4 5 60 1 2 3 4 5 60 1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 7 80 1 2 3 4 5 6 7 80 1 2 3 4 5 6 7 8 90 1 2 3 4 5 6 7 8 90 1 2 3 4 5 6 7 8 90 1 2 3 4 5 6 7 8 9 100 1 2 3 4 5 6 7 8 9 100 1 2 3 4 5 6 7 8 9 100 1 2 3 4 5 6 7 8 9 10 110 1 2 3 4 5 6 7 8 9 10 110 1 2 3 4 5 6 7 8 9 10 11 120 1 2 3 4 5 6 7 8 9 10 11 120 1 2 3 4 5 6 7 8 9 10 11 120 1 2 3 4 5 6 7 8 9 10 11 12 130 1 2 3 4 5 6 7 8 9 10 11 12 130 1 2 3 4 5 6 7 8 9 10 11 12 130 1 2 3 4 5 6 7 8 9 10 11 12 13 140 1 2 3 4 5 6 7 8 9 10 11 12 13 140 1 2 3 4 5 6 7 8 9 10 11 12 13 14 150 1 2 3 4 5 6 7 8 9 10 11 12 13 14 150 1 2 3 4 5 6 7 8 9 10 11 12 13 14 150 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 170 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 170 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 180 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 180 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 180 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Ang
le o
f Ar
20-15-10
-505
-15 dB
-15 dB-3 dB
Time of Arrival (μ seconds)0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
-20
TanDEM-L
Diameter 15m
Focal length 13 5 mFocal length 13.5 m
Offset (elevation) 9 m
Azimuth elements 6
Elevation elements 32 (or 40)
Azimuth Spacing 0.6
Elevation spacing 0.6816
Elevation Scan Approximately ±8°SCF01 Electronic Scanned Array Design
Slide 235of 255
Elevation Scan Approximately ±8°
TanDEM-L Feed Designsg
6.5
0.9
5.2
0.9
• Standard feed for 7 meter • Enhanced feed shape resolution
• Performance degrades at d f
pdesigned to capture >80% of received powerSh d t ffnear and far range
• Supports three azimuth channels
• Shape corresponds to off-axis aberration of parabolic reflectorchannels p
Slide 236of 255SCF01 Electronic Scanned Array Design
Deformation, Ecosystem Structure and Dynamics of Ice DESDyni (JPL)Dynamics of Ice DESDyni (JPL)
• A dedicated U.S. InSAR and LIDAR mission optimized for studying hazards and global environmental change.L b d th ti t d (SAR) t• L-band synthetic aperture radar (SAR) system– Operated as a repeat-pass interferometer (InSAR)– Multiple polarization: single dual or fully polarimetric– Multiple polarization: single, dual, or fully polarimetric– Strip-map or scanSAR (SCORE) modes with a viewable swath
of 340 km– 35 m ground resolution– Two sub-bands separated by 70 MHz for ionospheric correction
SCF01 Electronic Scanned Array DesignSlide 237
of 255
DESDyni Reflector Concept
flResource Reflector
Instrument Mass 600 kg
Instrument Power 1600 wattsInstrument Power 1600 watts
Dimensions 15 meter diameter~4 x 0.5 meter feed
SCF01 Electronic Scanned Array DesignImages courtesy NASA/JPL-Caltech desdyni.jpl.nasa.gov/files/DESDynI_RadarDes&PerfV4a.pdf
Slide 238of 255
Feed Structure Also Contains Electronics and Thermal Management SystemThermal Management System
Next Generation Geodetic Imaging with Interferometric SAR: Toward InSAR Everywhere, All the Time
SCF01 Electronic Scanned Array Design
g g y ,Paul A. Rosen, Jet Propulsion Laboratory, California Institute of TechnologyUNAVCO Workshop, Boulder, Colorado, March 10, 2010
Slide 239of 255
DESDynI Modely
SCF01 Electronic Scanned Array DesignSlide 240
of 255
DESDynI Model Parametersy
R fl t di t 15 t j t d i b di ti• Reflector diameter 15 meter projected in beam direction (actual reflector is elliptical)
• Focal Length is 10 metersFocal Length is 10 meters• Array feed of 24 conical horns, distributed on 2.2 meter
centers at focal plane position with 40 degree taper p p g pangle and 12 dB taper– Feed design would be optimized for Efficiency/Spillover during
detailed designdetailed design• No struts or other obstructions which tend to raise
sidelobes• Used Ticra Grasp software (full version)
– These cases can run on student version if each feed element is separately analyzed (24 cases) and results summedseparately analyzed (24 cases) and results summed
SCF01 Electronic Scanned Array DesignSlide 241
of 255
Feed Pattern Over-illuminates ReflectorReflector
1Spillover
0.95
Relative PowerSpill Over (dB)
0 85
0.9
0.8
0.85
0 7
0.75
0.65
0.7
SCF01 Electronic Scanned Array Design0 5 10 15 20 25
Element Number
Slide 242
of 255
Individual Beam Patterns Elevation Cut
50Array Feed Element 12 Far-field Principal Plane Cuts
6
30
40
50
0.6
0.1
→ ←→ ←Individual FeedElevation Cut
Azimuth Cut
20
30
0
10
-20
-10
-40
-30
1.0° 3 dB beamwidth1 0 3 dB b h i h
Effective Array Width (λ/θ) = 12.2 metersEff i A H i h ( / ) 12 2
SCF01 Electronic Scanned Array DesignSlide 243
of 255-50 -40 -30 -20 -10 0 10 20 30 40 50
-50
1.0° 3 dB beamheight Effective Array Height (λ/θ) = 12.2 meters
Transmit Beam Comprises Sum of 24 FeedsFeeds
50Combined Feeds Elevation Plane Cut
40
50→ ← Individual Feed Summation
20
30
10
20
10
0
-20
-10
13 9 3 dB b h i hEffective Array Width (λ/θ) = 13.6 metersEff i A H i h ( / ) 0 9
SCF01 Electronic Scanned Array Design-50 -40 -30 -20 -10 0 10 20 30 40 50
-3013.9° 3 dB beamheight Effective Array Height (λ/θ) = 0.9 meters
Slide 244of 255
24 Element SumPrincipal Plane CutsPrincipal Plane Cuts
50Combined Feeds Principal Plane Cuts
40
50→ ←→ ← Individual Feed SummationElevation Cut
Azimuth Cut
20
30
10
20
10
0
-20
-10
0.9° 3 dB beamwidth13 9 3 dB b h i h
Effective Array Width (λ/θ) = 13.6 metersEff i A H i h ( / ) 0 9
SCF01 Electronic Scanned Array Design-50 -40 -30 -20 -10 0 10 20 30 40 50
-30
13.9° 3 dB beamheight Effective Array Height (λ/θ) = 0.9 meters
Slide 245of 255
Beam Width VariationReflector vs ESAReflector vs ESA
6Individual Beam Size
6Individual Beam Size
5
Beamwidth AzimuthBeamwidth Elevation
5
Beamwidth Azimuth ReflectorBeamwidth Elevation ReflectorBeamwidth Azimuth ALOS-2Beamwidth Elevation ALOS-2
44
3
dB s
ize
( °)
3
dB s
ize
( °)
2
3-d
2
3-d
11
SCF01 Electronic Scanned Array Design-10 -5 0 5 10
0
Scan Angle (°)
-40 -30 -20 -10 0 10 20 30 400
Scan Angle (°)
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Reflector Beam Gain Variation
0.315°
Array Feed Elements Far-field Pattern Contour
42 dB46
Elemental Beam Gain
0.1
0.2
5°
10°
15° 42 dB39 dB36 dB33 dB30 dB
42
44
0V
-5°
0°
5
40
Gai
n (d
B)
-0.2
-0.1
15°-15° 10°
-10°
5°
5
0° 5° 10° 15°
36.536.5Individual Feed Patterns20141215Job_03offset_reflector_array
36
38
-0.3 -0.2 -0.1 0 0.1 0.2 0.3U
-15° -10° -5° 0° 5° 10° 15°
0 5 10 15 20 2534
Element Number
• Beam broadening and gain reduction are directly related• Beam broadening and gain reduction are directly related
SCF01 Electronic Scanned Array DesignSlide 247
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Equivalent Aperture Sizes for Reflectorq p
Array Feed Element 24 Reflector Current Contour
6-3 dB width = 8.7 meters-3 dB height = 8.0 meters
-34 dB-38 dB-41 dB-46 dB
2
446 dB
0
2
Y (m
)
-31.2
-2
-6
-4Feed 2420141215Job_03offset_reflector_array
SCF01 Electronic Scanned Array DesignSlide 248
of 255-6 -4 -2 0 2 4 6
X (m)
Currents in Reflector
Array Feed Total Contour
6-3 dB width = 8.5 meters-3 dB height = 3.5 meters
-13 dB-17 dB-20 dB-25 dB
2
425 dB
-30 dB
0
2
Y (m
)
-2-10.3
-6
-4
Individual Feed20141215Job_03offset reflector array
SCF01 Electronic Scanned Array Design-6 -4 -2 0 2 4 6
X (m)
offset_reflector_array
Slide 249of 255
L-band Summaryy
• Array size– Array height of 4 meters matches Tx requirement well
Array height of > 4 meters advantageous for Rx– Array height of > 4 meters advantageous for Rx– Array length of ~ 10 meters compatible with azimuth resolution of
~ 3 - 10 meters
• Scan Capability– Elevation beam agility required for good area coverage
(S SAR/SCORE S SAR )(SweepSAR/SCORE, ScanSAR, etc)– Azimuth beam agility enables additional modes (TOPSAR)– Beam agility required for spotlight modesBeam agility required for spotlight modes– Reflectors have limited azimuth steering
SCF01 Electronic Scanned Array DesignSlide 250
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Feeds
• Feed for reflector needs beam shaping to for acceptable efficiency in both Rx and TxA f d h id bl hi h d it th• Array feeds have considerably higher power density than ESAs complicating cooling
• Large number of TRM’s in ESA provides degrees of• Large number of TRM s in ESA provides degrees-of-freedom necessary for advanced beam control
SCF01 Electronic Scanned Array DesignSlide 251
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Launch Constraints
• Reflector antennas are more amenable to folding required for launch
Provide higher gain in receive– Provide higher gain in receive
• ESA antennas up to 3.5 x 10 meters have been designed for foldingdesigned for folding
SCF01 Electronic Scanned Array DesignSlide 252
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References
Ph d A A t H db k S d Editi b R b t J M ill 508 A t h• Phased Array Antenna Handbook, Second Edition by Robert J. Mailloux, 508 pages, Artech House, 2nd edition (March 31, 2005) (originally published in 1994)
• “Electronically scanned array” in Synthesis Lecture on Antennas, R. J. Mailloux, Morgan & Claypool Publishers, 2007.y
• Radar Handbook, Third Edition by Merrill Skolnik, 1328 pages, McGraw-Hill Professional, 3rd edition (January 22, 2008) (originally published 1970)
– Chapter 12 Reflector Antennas by Michael Cooley and Daniel Davis
– Chapter 13 Phased Array Radar Antennas by Joe Frank and John D. Richards
• Antenna Theory Analysis and Design by Constantine Balanis, 790 pages, Harper & Row 1982• Practical Phased Array Antenna Systems (Artech House Antenna Library) (Paperback) by Eli
Brookner 320 pages Artech House (December 1 1991)Brookner, 320 pages Artech House (December 1, 1991) • Phased Array Antennas (Wiley Series in Microwave and Optical Engineering) (Hardcover) by R.
C. Hansen (Author) 504 pages Wiley-Interscience (January 19, 1998) (originally published in 1966)
• Introduction to Airborne Radar by George W. Stimson, 584 pages, SciTech Publishing, 2nd Edition (January 1, 1998) (originally published in 1983)
• Electronically Scanned Arrays MATLAB® Modeling and Simulation by Arik D. Brown, 224 pages, CRC Press (May 3 2012)CRC Press, (May 3, 2012)
• Antenna Arrays: A Computational Approach by Randy L. Haupt, 534 pages, Wiley-IEEE Press (April 12, 2010) SCF01 Electronic Scanned Array Design
Slide 253of 255
Web Based References
• EW and Radar Handbook– https://ewhdbks.mugu.navy.mil/home.htm
D D id C J l t lid d M tL b d• Dr. David C. Jenn lecture slides and MatLab code– http://www.nps.navy.mil/Faculty/jenn/
• Jet Propulsion Laboratories• Jet Propulsion Laboratories– http://southport.jpl.nasa.gov/
• Microwave 101• Microwave 101– http://www.microwaves101.com/index.cfm
• Electromagnetic Waves and Antennas – Sophocles J.Electromagnetic Waves and Antennas Sophocles J. Orfanidis– http://www.ece.rutgers.edu/~orfanidi/ewa
SCF01 Electronic Scanned Array DesignSlide 254
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Thank you for your attention
SCF01 Electronic Scanned Array DesignSlide 255
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