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June 2005
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NTD Developments Overview

• For MNRF Symposium 7 June 2005

Presented by Colin Jacka 7 June 2005
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Requirements from MNRF Grant

• Stated aims at 2002 MNRF initiation
• To develop multi-beaming antenna technology
• Advanced optical signal transport
• Advanced signal processing schemes
• Developing interference mitigation techniques
• Integrated into an operating instrument which
  would benefit the development path towards the
  SKA
• Would make use of project deliverables from other
  MNRF-funded projects eg CABB, MMIC, SKA Siting

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MNRF Progress to date

• Original NTD Project Plan
• Choose NTD concept by 30 June 2004
• From that point on, the effort has been on FPAs
  using parabolic dish antennas
• Revised Preliminary NTD Project Plan 30 September
  2004
• Roadmap towards SKA maximising Australias
  participation
• NTD providing prototyping and design for xNTD,
  because
• xNTD could be a typical SKA station

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SKA Roadmap The route forward

• extended New Technology Demonstrator
• Outline
• 20 x 15m dishes at WA site
• Complete by 2008
• MNRF/WA/CSIRO support
• Goals
• Maintain Australian radioastronomy at forefront
  of world science
• Maximise influence in SKA project
• Science
• Technology
• Siting
• Deliver outcomes for industry
• FPA/Digital beamforming
• Data-mining

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NTD and xNTD - Proposals

• extended New Technology Demonstrator
• Objectives
• Key item in the strategy of maximising
  Australias participation in the SKA (objective
  in CSIROs 2003-2006 Strategic Plan, and ATNFs
  SKA Roadmap)
• To build a new world-class radiotelescope at the
  Australian SKA site
• Telescope in its own right, with a lifetime of 5
  years, operated by ATNF as a National Facility
• But also a prototype for the SKA
• Risk mitigation for the International SKA
  Pathfinder (ISKAP), and leveraging of
  international funds

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What difference does the x make?

• NTD
• Funded by existing, secured ATNF MNRF funds
• 2 interconnected dishes, 15m diameter, each with
  focal plane array, at proposed SKA site
• xNTD
• Additional funding from CSIRO, ATNF, WA State
  Gov, (and still soliciting others)
• 20 dishes, 15 m diameter, arranged in one group,
  genuine micro-SKA, at proposed SKA site
• Project Plan Design Development Program until
  early 2006 is common for NTD and xNTD
• xNTD implementation phase from Jan 2006, as a
  result of sufficient risk mitigation in areas of
  antenna, FPA, digital beamforming and correlator
  design

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NTD/xNTD Project Strategy
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Challenges for xNTD

• List of (technology) challenges that we keep in
  mind, and note that NTD should allow us to tackle
  some of them
• Can we make small steerable dishes cheap enough?
• Cheap, high performance (wide band and
  polarization pure) FPAs?
• Cheap, high performance integrated RXs?
• No self-generated RFI from RXs (or rejection
  schemes)?
• How to transport signals from FPA?
• DBF (efficient, cost-effective using FPGAs)?
• Calibration with synthesized varying beam
  patterns?
• Correlator (a very large effort)
• Data storage transportation
• Remote operation as a NF from East Coast of Oz?
• But also we note that
• Many other large projects currently on-going
• Shortage of key people

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So, where are we now?

• (time marches on, but) we have made substantial
  progress in a number of areas
• Antennas for NTD
• RXs for NTD
• FPA for NTD
• Digital H/W for NTD beamformer and design of xNTD
  correlator
• Interferometer experiment _at_ Marsfield

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NTD Antenna System

• Presently looking at 3 alternatives to meet the
  challenge of performance/cost
• The Indian PPD dish design
• New design using manufacturing techniques
  available in Australia
• Refurbishing 2 antennas from Fleurs (for NTD)
• All are on-going investigations for xNTD
  purposes, but for the NTD we are going with the
  ex-Fleurs antennas

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(1) Indian PPD Reflector Prototype
Photos from Ken Skinner of SES
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(2) Reflector antenna options

• Custom-built mesh reflector using NC machine
  tools
• High-tech solution with high accuracy, good
  repeatability, and no tooling-up costs
• Local manufacture of prefabricated flat-pack
  reflector assemble on site
• Progress
• Engineering consultants have been contacted to
  provide structural engineering analysis and
  comments on proposal
• Manufacturers asked to comment on
  manufacturability issues of our design
• Bristow Laser Systems have demonstrated new CNC
  machinery which appear to be ideal for
  manufacture
• Advice being sought for patenting suitability of
  manufacturing methods

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(1) Reflector antenna options

• Refurbished dishes from the former Fleurs
  radiotelescope
• Two 13.8m dishes have now been removed from
  Fleurs and are being refurbished at SES
• SES is confident that the condition and design
  are sound
• New antenna drive system has been designed
• 2-element interferometer _at_ Marsfield
• Sites chosen for antennas at Marsfield, and
  infrastructure design has commenced
• Expect antennas to be on site at end of July, and
  we are preparing infrastructure to meet that date
  for installation
• Project milestone for the installation to be
  ready for experiments by end of October

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Fleurs dishes
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Focal Plane Arrays

• John O Sullivan
• THEA tile for initial NTD experiment
• Bunny ears concept for increased bandwidth
• John Kot
• Access to Uni of Mass s/w
• Fundamentals, modelling use of other s/w
• Stuart Hay
• Some other interesting ideas, eg foveated arrays
• Douglas Hayman
• Various other performance measurement
  investigations
• Interest for collaboration in RD from Canadians,
  Sth Africans, Astron, UKSKADS

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FPA options

• Collaborative development of Vivaldi array with
  ASTRON / U.Mass.
• Appears to be quickest option for short-term
  demonstrator
• Have price from ASTROM for delivery of THEA tile
• Agreement with U.Mass Astron for use of s/w for
  both NTD xNTD development
• Attendance at FPA workshop at Astron in June
• Increase our involvement with other international
  FPA developments
• Alternate wideband arrays
• Looking at promising rabbit ears design
• Inherently wideband structures
• Foveated array with natural scaling of FoV
• Looking at wider system integration aspects of
  optimisation of FPA elements, LNAs, RX

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Receiver

• (200 RXs per dish equipped with FPA)
• Prototype receiver design has been completed,
  development and testing
• Some modifications discussed for use at
  congested radio spectrum at Marsfield
• Separate LNA for Tsys requirements being
  undertaken

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Digital Signal Processing

• Designs have been refined such that they can
  efficiently handle
• A 20-antenna xNTD using 10x10 element dual
  polarisation FPAs
• A 500-antenna LFD (MIT Haystack) _at_ Mileura
• A SKAMP-3 with 96 antennas
• An LFD with only 48 antennas (LFD fallback _at_
  Mileura)
• All require a correlator
• NTD, xNTD and SKAMP require a digital beamformer
  for each antenna
• While LFD requires a digital receiver
• Whitepaper shows commonality in the NTD
  beamformer and the LFD RX
• Sth Africans also interested, but assessing other
  options as well

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Digital Signal Processing

• Digital Beamformer design one for each
  polarization on each antenna
• A considerable amount of h/w required to meet
  xNTD specs, but NTD is being used to mitigate
  risks,
• should only build h/w where it has value (rather
  than simulation, theory, paper designs), eg need
  inputs from all RXs for FPA analysis, but we
  dont really need to have 48 beams on NTD. So NTD
  beamformer to have less beams.
• Prototype NTD beamformer has 24 MHz bandwidth,
  and 24 inputs (final DBF requires 250 MHz
  bandwidth and 200 inputs)
• Status
• Daughter Boards are being populated
• Motherboard (supporting 6 daughter boards) is
  being manufactured
• 1st stage PFB (for full DBF) has been designed
  debugged in Xilinx

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NTD beamformer

• Input data rate for one polarisation from 10x10
  FPA from one xNTD antenna is 100x256Mx2x8 409.6
  Gbps
• Output data rate is reduced by 4 100 Gbps
• (but 20 antennas and 2 polarisations means an
  output data rate of 4 Tbps to the correlator)

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Possible xNTD correlator

• Need smart design to avoid the routing of the
  data strangling the design
• Design approach is to use a correlator cell that
  minimises i/o requirements
• 1 Virtex 4 XILINX FPA chip processes 48 frequency
  channels for all 20 xNTD antennas simultaneously.
• Full xNTD correlator (48 beams) requires
• 24 correlator boards, each with 16 mid-sized
  XILINX chips
• 72 Buffer boards, each with 5 Xilinx chips and 16
  memory chips

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Some Influential Milestones

• Endorsement of SKA Roadmap by ASKACC (done)
• Australian SKA site selection NSW/WA Nov 04
  (done)
• Approval by AABoM and DEST for revised NTD plan
  (done)
• Australian inter-departmental SKA Steering
  Committee report Feb-Mar 2005 (done)
• Secure additional CSIRO funding (done)
• GO/NO-GO Decision for xNTD at Dec 2005 (Mar 2006)
• SKA international site selection end 2006

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Focal Plane Arrays for the New Technology
Demonstrator

• John Kot, Stuart Hay, Nasiha Nikolic, Doug
  Hayman, Christophe Granet

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NTD FPA system
Individual FPA element has high TA due to
spill-over
Analogue receiver
To correlator
Mutual coupling and reflections in the array
reflector system
Quantization digital beamforming to generate
low TA antenna beams
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Focal field overlaid with array
?
?
800MHz 1.9 scan
1800MHz 2.6 scan

• Contours at -6 and -10dB
• Number of elements required to form a beam
  estimate
• About 8 elements in both cases should give a
  basic beam
• More are required to clean up the beam and
  increase efficiency
• For a full critical sampling at 1800MHz, about 16
  elements are needed at 800MHz

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Basic FPA Operation

• The diameter of the focal spot
• Reflector beamwidth
• To 1st order, FoV is constant across the band
• For a wideband FPA, to form high efficiency beams
  at the low-frequency end of the band requires
  summing inputs from many elements
• For off-axis beams, focal spot offset increases
  with f/D, while coma decreases
• For a given FPA diameter and FoV there is an
  optimum f/D
• Element spill-over temperature is high receiver
  gain must be reduced to avoid clipping in A/D
  converter

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FPA Size vs. F/D

• Optimum F/D depends on quality of edge beams
• For half scan of 4
• 3dB loss 0.35 0.4
• 1dB loss 0.4 0.5

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Low noise operation with a wideband, uncooled FPA

• FPA element impedance is strongly determined by
  array effects (tendency for large variations with
  frequency)
• For a small FPA of identical elements, the
  element impedances are all different (modulo
  symmetry)
• LNA noise contributions self noise coupled
  radiated noise from all other LNAs
• We need to do a lot of work to understand how to
  achieve optimum low noise operation it is far
  from straight forward

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Ongoing efforts towards an NTF FPA

• CSIRO has signed an agreement with U. Mass. and
  ASTRON for joint development of a Vivaldi FPA
  for 800MHz 1.8GHz
• Avoid re-inventing the wheel
• Mitigate a major risk with the NTD project
• Development of a model for a narrow band
  egg-crate array of dipole feeds with a
  reflector
• Gives us a simple, analytic model to study
  representative FPA effects such as noise
  coupling element spacing offset between
  dual-polarized array elements interaction
  between array and reflector (cavity effect)
• Allows us to explore more of the parameter space
  than currently possible with a finite element /
  boundary element computational model

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Ongoing efforts towards an NTF FPA (2)

• Investigation of alternative array elements
  tilings
• Non-ideal aspects of uniform Vivaldi arrays
  polarization and large excursions in element
  impedance
• Other elements may be better, e.g. arrays derived
  from self-complementary screens have very large
  impedance bandwidth
• Non-uniform arrays may compensate for small
  array effect, or offer much larger bandwidths
  (foveated arrays)
• Close cooperation between antenna, RF, and DSP
  engineers to understand system aspects of FPA
• Investigation of options such as balanced vs.
  conventional LNA
• Understanding of how array reflector choices
  affect beamformer complexity

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Ongoing efforts towards an NTF FPA (3)

• Development of a comprehensive LNA FPA
  reflector model, using a generalized scattering
  matrix model
• Will allow us to investigate beamforming for
  optimization of A / Tsys taking into account
  effects such as noise coupling and cavity effect,
  using accurate models for FPA and reflector and /
  or measured results

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The End