Electronic Scanned Array Design · 2016-09-27 · – First sidelobe at -17.8 dB – 3 dB beamwidth = ± 1.03 λ/D – first null at ± 1.22 λ/D From Balanis “Antenna TheoryAntenna

Electronic Scanned Array DesignSCF01

John S. Williams

The Aerospace Corporation (retired)

[email protected]

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


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


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)


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


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


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°


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

of 255

Aperture Design


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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


of 255

Basic Aperture Shapesp p

b

a

bbbbbbbbbbb

aaaaaaaaaaa

bb

aa

bbb

aaa

bbbb

aaaa

bbbbb

aaaaa

bbbbbb

aaaaaa

bbbbbbb

aaaaaaa

bbbbbbbb

aaaaaaaa

bbbbbbbbb

aaaaaaaaa

bbbbbbbbbb

aaaaaaaaaa

• 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


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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


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


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Another Visualization

4λ

SCF01 Electronic Scanned Array Design 2D²/λ3λSlide 16

of 255

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


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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


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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


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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


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.


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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)


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ESA Design Approach


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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


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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


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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


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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


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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


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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)


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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


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Beam Pattern Analysis


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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


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)


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)


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


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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


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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))


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


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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


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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


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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


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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, . . .


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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


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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


-8

-6

-4

2


-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


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


-1.9

0

)

0.8


-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)


-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°


B)

10

20

Beamwidth = 3.0°


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


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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)


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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:


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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%


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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


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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


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


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


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


of 255

Grating Lobes andGrating Lobes andThinned Arraysy


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


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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)


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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)


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)


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


-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)


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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


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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


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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


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Second PartSecond Part


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Beam Pattern Synthesis


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


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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


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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)


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


8

10

12

λ = 3 cmM = 12Δx = 1.5 cm

)

Real

4

6

AF

(vol

ts)


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


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.


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


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


of 255

Uniform Weighting (unweighted)g g ( g )

• Simplest• Default condition for transmit• Highest gain


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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°


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


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


-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%


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°


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


of 255

Binomial Example (M=11)p ( )

Binomial Method Binomial Method

-20

-15

-10

-5


M = 11Δx = 1.5 cm

B)

Imaginaryλ = 3 cmM = 11Δx = 1.5 cm


-45

-40

-35

-30

-25

Sidelobe at -81°

AF

(dB

Real

-90 -60 -30 0 30 60 90-50

Sidelobe is -326 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


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°


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.


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


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)


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


3 4Slide 90

of 255

Dolph-Chebyshev Example (M=11)p y p ( )

Chebychev Method Chebychev Method

-20

-15

-10

-5


M = 11R = 20 dB

B)

yImaginary

λ = 3 cmM = 11R = 20 dB

y


-45

-40

-35

-30

-25

Sidelobe at -16°

AF

(dB

Real

-90 -60 -30 0 30 60 90-50

Sidelobe is -20 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


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°


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. .


of 255

Taylor Example (M=11)y p ( )

Taylor Method Taylor Method

-20

-15

-10

-5


M = 11R = 20 dBn-bar = 5

B)

yImaginary

λ = 3 cmM = 11R = 20 dBn-bar = 5

y


-45

-40

-35

-30

-25

Sidelobe at -16°

AF

(dB

Real

-90 -60 -30 0 30 60 90-50

Sidelobe is -20 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


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°


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


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


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


of 255

Fourier Transform – First Null

Fourier Method Fourier Method

-20

-15

-10

-5


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



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


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


of 255

Fourier Transform – Second Null

Fourier Method Root real imaginary magnitude angle

-20

-15

-10

-5


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


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


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Fourier Transform – Third Null

Fourier MethodRoot real imaginary magnitude angle

1 5.722 + 0.000i | 5.722 0.0°

-20

-15

-10

-5


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


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


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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


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)


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


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°


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Quadratic Beam Spoilingp g

• Not a synthesis technique• Apply systematic phase error at each element


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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


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Quadratic Phase Examplep

Quadratic Phase Method Quadratic Phase Method

-20

-15

-10

-5


M = 11Δx = 1.5 cm

B)



-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°


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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


* 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


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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


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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


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


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


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


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)


of 255

Reflector Applications


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


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)


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


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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


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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


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)


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


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)


of 255

PART THREEPART THREE


of 255

Practical Designg

• Theory in Matlab with high precision and no errors• Need to approximate ideal components• Electronics advances have made this possible


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


of 255

Radiating Elements


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


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


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Radiating Element Requirementg q

• Wide angle radiation pattern• Low cost• Readily arrayed• Compatibility with feed and t/r modules


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


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


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


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


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


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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


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.


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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


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


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


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


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


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


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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


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


of 255

Patches

• Used by– Iridium

JPL L band designs– JPL L-band designs– Cosmo-Skymed– SEOSAR/PAZ

• Well suited to integration with array


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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


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


g– Allows computation of scan patterns on next page

Illustrations from Byström (© Ericsson Microwave Systems) Slide 147of 255


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


of 255

T/R Modules


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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


of 255

Two Types of Transmit / Receive ModulesModules

T/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 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


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


Illustration from George Stimson (© SciTech Publishing, Inc)Slide 153

of 255

Raytheon T/R Module for THAADy


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.


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.


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


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


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


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


(L2 " sinazimuth "H2 " sin elevation)/62 = (Area2 " sinazimuth " sin elevation)/62

Slide 160of 255

TELA TDU Module


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

- -


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


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


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)


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


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


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


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


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


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


of 255

7-21 GHz Dual-Polarized Arrayy


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


of 255

Technology Base and Cost


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


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


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), , ( )


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, …)


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


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


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


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


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


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


of 255

PART FOURPART FOUR


of 255

ESA Examples


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


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


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°


of 255


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


Images © Boeing CorporationSlide 194

of 255

ESAs in Space


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


of 255

Iridium Beams in U-V Spacep


of 255

Iridium Beams on Globe


of 255

Iridium Beam on Globe (detail)( )


of 255

Iridium Beams projected to Groundp j


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


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


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)


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


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


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


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


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


of 255

Antenna Beams on Globe


of 255

Antenna Beams on Globe (detail)( )


of 255

Antenna Beams Projected to Ground


of 255

L-Band Trade Study


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)


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


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


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


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


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


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


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


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


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


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 (°)


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


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


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


of 255

OFFSET REFLECTOR


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


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


g g y ,Paul A. Rosen, Jet Propulsion Laboratory, California Institute of TechnologyUNAVCO Workshop, Boulder, Colorado, March 10, 2010

Slide 239of 255

DESDynI Modely


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


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


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 (°)

Slide 246

of 255

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


of 255

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


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


of 255

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


of 255

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


of 255

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


of 255

Thank you for your attention


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Documents

Electronic Scanned Array Design · 2016-09-27 · – First sidelobe at -17.8 dB – 3 dB beamwidth = ± 1.03 λ/D – first null at ± 1.22 λ/D From Balanis “Antenna TheoryAntenna