focal plane array related activities at...

ICT Centrewww.ict.csiro.au/antennas

Focal Plane Array Related Activities at CSIRO

Trevor S. Bird(1), Douglas Hayman(1), Suzy Jackson(2) & Dick Ferris (2)

(1) CSIRO ICT Centre(2) CSIRO Australia Telescope National Facility

PO Box 76, Epping NSW 1710 AustraliaEmail: [email protected]

www.ict.csiro.au

Focal Plane Array Workshop

Outline of Presentation

Past experience with focal plane arraysCSIRO and other activities related to FPAsAntennas– SKA proposals– FPAs– Line feeds

Integrated receiver systemsHigh-speed digital correlatorsWhat CSIRO brings to collaboration with Europe– Design– Measurement

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Parkes Multibeam Receiver SystemMultibeam receiver system sits in the telescope’s focus cabin and receives signals from space

Radio signals from galaxies in space hit surface of telescope and are reflected to focus cabin

Telescope detects faint galaxies

Telescope ‘sees’ 13 patches of sky simultaneously

(Data for the Southern sky)

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Arecibo Multibeam Feed System

Successfully installed in April 2004

Feed array (1.225 – 1.525 GHz)under test at CSIRO

Arecibo radio telescope

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Arecibo Multibeam Feed Array –Sample Results

Theory

Element 3 : Array reference 45°, OMT horizontal. 135°-plane at 1.225 GHz & distance 3.7m

1

2

3

4

56

7

Theory

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Current Australian Radio Astronomy Projects with FPAs

FARADAY and PHAROSMUDDA – multi-use dense digital arrayAustralian SKA Concept Demonstration Projects– MMIC development– Signal processing– Australia Telescope Compact Array Broadband Backend

(CABB)Bandwidth increased from 128MHz to 2GHz

– SKAMP – SKA Molonglo prototype– NTD – new technology demonstrator

Remote and radio-quiet site– Luneburg lens development– Techniques for RFI mitigation

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Antennas

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SKA Configurations

Technical and cost assessmentsLuneburg lensCylindrical reflectorWide-field of view (WFOV) reflector

Luneburg lens

Cylindricalreflector

WFOV reflector

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Prototype Luneburg Lens Construction

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Measurement of Prototype Luneburg Lens

Aperture field

Far field

Measured results in S-band

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Luneburg Lens with Egg-crate FPA

The ASTRON FARADAY FPA we had on site was used as an illuminator for the Konkur lens.

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Cylindrical Reflector

Offset-fed optionsImproved cost modelWideband line-feed development (with Sydney Uni.)

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WFOV Reflector

FOV ~10º x 10º~14m diameter reflectorLarge array in focal regionArray is extendableTechnology is well developed and cost known

Three CSIRO MultiBeam antennas at SES-ASTRA, Luxembourg.Each antenna covers a ~40º x 1ºFOV.

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Focal-plane Arrays

Prototype focal plane array of Vivaldi elements

All SKA are expected to use focal-plane arraysFocal-plane arrays:– Allow formation of

multiple beams– Correct for errors in

reflectors or lenses– Allow electronic

beam scanning

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Approach to Focal Plane Feeds

Compact feed elementsClose packing (max. spacing < 0.9λ)WidebandDual polarizationRigorous analysis including mutual couplingExcitation chosen to maximize secondary antenna Aeff/T (G/T)

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Focal Plane Feed Options

Array cluster per beamSingle feed per beam

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Cluster Feed Approach

Choose array excitation to maximize G/TAOverlap sub-arrays

– trade-off between number of elements and efficiency

Combine signals at:– RF– IF– M x N processor

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Overlapping Sub-arrays

Example: 3 overlapping hexagonalarrays

Efficiency improvement is terraced,for example:

504030201000

20

40

60

80

100

No. of ElementsB

eam

eff

icie

ncy

%

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Array Excitation forMaximum G/TA

Antenna gain

G(θ,φ)= GoQ(θ,φ)* Q(θ,φ)

Pf= Go

(cx)† (c x)x† x

c = correlation coefficients between the focal field and co-polar modes in the aperturesx = normalized array excitation coefficient vector

Note: Gain is maximum when x

Zero cross-polarization in beam direction when

where d is similar to c except for cross-polar modes

.= c†

x = c† −d c†

dd† d†

Antenna temperatureTA =

14π

G(θ,φ) T(θ,φ)Ω∫ dΩ = Go

x† B xx† x

For a given beam direction (θ,φ), G/TA is maximum when

x = B−1 c†

Mutual coupling between feed elements is included.

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Potential Elements for Close Packed Arrays

Coaxial waveguide (b/a>0.4)Dielectric rodMicrostrip patchHelicalTravelling-wave slot antennasVivaldi– Balanced– Anti-podal

b

a

(Qassim & McEwan)

x

ychoke ring

input probe

top patch

driven patch

ground plane~0.8λ

~0.25λ

x

ychoke ring

input probe

top patch

driven patch

ground plane~0.8λ

~0.25λ

(after Kiskh & Shafai)

-A

A

truncation limits

y

x

y=±Aexp(Rx)

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Arrays of Coaxial Horns

54.0

40.8

40.8

72.0

90.0

Y

X

E1

E2

1

3

2

28.8

-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

3 4 5 6

Frequency GHz

Cou

plin

g co

effic

ient

dB

S12 (theory)S13 (theory)S12 (expt)S13 (expt)

Validation of analysis

Mode matching method for coaxial horns Accurate mutual coupling analysis (Bird, Trans. IEEE, Mar. 2004, pp. 821-829)In compact arrays

where s is the element spacing in wavelengths < 0.9 Example: s < λ/2, b/a > 0.3

80.0

153.0

46.0

3 2 1

Low-loss polystyrene foam spacers

123

Irises

280.0

X

Y

75.0

173.2

86.6150.0

75.076.5

895

514

1

2 3

4

All dimensions in mm

Feed element for Jodrell Bank Lovell radio telescope

2sa

))a/b(1(1

<λ

<+π

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Balanced Anti-podal Vivaldi Antenna

E-plane

H-plane

With dielectric Without dielectric

Computations by S. Hanham, CSIROWith CST Microwave Studio Cross-polarization is high

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Surface Currents on VivaldiElements

Conventional balanced Vivaldi Crossed balanced Vivaldi

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Integrated Receiver Systems

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MUDDA Overview – Frontend

Oversampled Focal Plane Array of 8x8 (nominal) tapered slot antennas for use on Parkes and other large unshaped dishes.RF frequency range 500 – 1700 MHz (nom).Tsys < 50K (uncooled).Instantaneous IF bandwidth 500 MHz.~40dB (6 – 8 bits) dynamic range.Dimensions 1.5m x 1.5m.

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MUDDA Overview - Backend

FPGA filterbank on each element.Beamformer for at least four independent beams.Located remotely from feeds – RFI issues.Use technology developed for CABB

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Possible Block Diagram

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Radio on a Chip

Takes advantage of low cost, low power RF-CMOS processes developed for wireless networkingWill integrate Mixer, IF filter, and Sampler, as well as LO distribution.Possibly integrating LNA, RF filter.Design with Cadence toolset (Macquarie Uni.)Integrations issues– CMOS inductor Q < 10 – bulk substrate– FET NFMIN ~40K for 0.25µ, ~20K for 0.18µ (2GHz) –

comparable with GaAs– Broadband LNA noise match.– Gilbert cell mixers.– Active IF filter.

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High-speed Digital Correlators

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2 GHz Bandwidth Correlator with Polyphase Filterbank

x0(m)

x1(m)

xρ(m)

xM-1(m)

xn

po(m)

p1(m)

pρ(m)

pM-1(m)

M-PointDFTviaFFT

0

1

ρ

M-1

X0(m)

X1(m)

Xk(m)

XM-1(m)

x0(m)

x1(m)

xρ(m)

xM-1(m)

xn

po(m)

p1(m)

pρ(m)

pM-1(m)

M-PointDFTViaFFT

0

1

ρ

M-1

X0(m)

X1(m)

Xk(m)

XM-1(m)

FFT

FFT

FIR

FIR

FilterbankFringeRotators CorrelatorsDMUX

FFT

FFT

FIR

FIR

FilterbankFringeRotators CorrelatorsDMUX

A 2GHz bandwidth polyphase digitalfilterbank with 4096 channels ... ... will fit into four XC2V6000 FPGAs

FPGA hardware may be completely

reprogrammed to produce many

different filterbank configurations, as

different observations may require.

2GHz

4k channels

4k channels

Multiple Zoom (>2 possible)

2GHz

4k channels

4k channels

Compound Zoom

2GHz

4k channels

Simple Zoom

2GHz

4k channels

Basic Configuration

FPGA hardware may be completely

reprogrammed to produce many

different filterbank configurations, as

different observations may require.

2GHz

4k channels

4k channels


2GHz

4k channels

4k channels


2GHz

4k channels

4k channels

Compound Zoom

2GHz

4k channels

4k channels

Compound Zoom

2GHz

4k channels

Simple Zoom

2GHz

4k channels

Simple Zoom

2GHz

4k channels

Basic Configuration

2GHz

4k channels

Basic Configuration

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Wideband Correlation

Build wider bandwidths by paralleling 2GHz slices8 GHz (per polarisation) high resolution spectrometer for MOPRA– 2GHz bandwidth per IF, four IFs per antenna

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Baseband Receiver / PoC Spectrometer1024 Channel Spectrum, DC-256MHz

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Molonglo Observatory Synthesis Telescope

Photo: G. WarrMaterial supplied by Anne Green, University of Sydney

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SKAMP - the Molonglo SKA Demonstrator

Two substantial demonstrator projects have been funded for installation on the Molonglo Telescope:– A 96-station, wideband FX correlator – A broad-band line feed system for a cylindrical

paraboloid.

These two projects constitute the SKA Molonglo Prototype – SKAMP. They will result in a significant trial of key SKA engineering elements and enhance the scientific value of the Molonglo TelescopeJoint venture between University of Sydney and CSIRO

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SKAMP Science Goals

Low-frequency radio spectrometry (300-1420 MHz)– Selection of objects via their radio spectral shape, e.g. candidate high

redshift (z>3) galaxies with ultra-steep radio spectra, study the formation of galaxies and massive black holes.

Redshifted HI (300-1420 MHz)– HI in absorption against bright continuum sources over a wide redshift

range (z=0 to 3). HI in emission - evolution of the HI mass function from z=0 to 0.5.

Low-frequency Galactic recombination lines– Recombination lines of carbon and hydrogen can be used to probe the

partially-ionized ISM.

Gamma Ray Bursters– Electronic beam steering gives a 5% chance of capturing a random event.

Concurrent SETI search, and Pulsars and Source Flux Monitoring

– 18 to 400 deg2 accessible around main beam. Real time de-dispersion

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The SKA Molonglo Prototype (SKAMP)

Collecting area = 1% of SKA (i.e. equivalent to 1 SKA station)

Multibeaming

Wide instantaneous field of view

Digital beamforming

Wide-band FX correlator(2048 channels)

Frequency and pointing agility

Line feed 0.3-1.4 GHz >100 MHz instant BW

Cylindrical antenna prototype

RFI mitigation strategies - adaptive noise cancellation

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Progress in Upgrade of Signal Path

Feed Development– modelling– feed synthesis– scan performance

Data Acquisition & Beamforming– Customised A/D

converters– delay & phase

tracking– data acquisition &

beamforming hardware installed in 2004

Correlator Development– Ball grid FGPAs– Testing in progress

Signal Processing– correlator control

computer (CCUBED) with external data interface has been setup

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‘Petal’ Line Feed Element

-150 -100 -50 0 50 100 150-40

-35

-30

-25

-20

-15

-10

-5

0

θ (degrees )

Amplitude (dB)

Me asure d Azimuth Patte rns for Ante nna Prototype , F=1539MHz

Co-polarX-polar

Elementpattern

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SKA New Technology Demonstrator (NTD)Aims:

Antenna, receiver and backend technology for support wide FOV, wideband astronomyOperational facility at a radio-quiet site– Demonstrate radio science opportunities in extremely

low RFI environment

Data transport/processing over long distances– Continent-wide, international connectivity

Remote energy provisionEnvironmental conditioning on a semi-arid remote site

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Concluding Remarks

Overview of projects in progressAntennasIntegrated receiversHigh-speed digital correlatorsDemonstrators in progressKeen to continue collaboration with Europe through PHAROS etc

focal plane array related activities at...

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