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June 2005. NTD Developments Overview. For MNRF Symposium 7 June 2005. Presented by: Colin Jacka 7 June 2005. Requirements from MNRF Grant. Stated aims at 2002 MNRF initiation: To develop multi-beaming antenna technology Advanced optical signal transport Advanced signal processing schemes

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Ntd developments overview

NTD Developments Overview

For MNRF Symposium 7 June 2005

Presented by: Colin Jacka

7 June 2005

Requirements from mnrf grant
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

Mnrf progress to date
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 Australia’s participation

        • NTD providing prototyping and design for xNTD, because

        • xNTD could be a typical SKA station

Ska roadmap the route forward
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

Ntd and xntd proposals
NTD and xNTD - Proposals

  • extended New Technology Demonstrator

  • Objectives:

    • Key item in the strategy of maximising Australia’s participation in the SKA (objective in CSIRO’s 2003-2006 Strategic Plan, and ATNF’s 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

What difference does the x make
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

Challenges for xntd
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

So where are we now
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 @ Marsfield

Ntd antenna system
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

1 indian ppd reflector prototype
(1) Indian PPD Reflector Prototype

Photos from Ken Skinner of SES

2 reflector antenna options
(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

1 reflector antenna options
(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 @ 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

Focal plane arrays
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 R&D from Canadians, Sth Africans, Astron, UKSKADS

Fpa options
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


  • (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

Digital signal processing
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) @ Mileura

    • A SKAMP-3 with 96 antennas

    • An LFD with only 48 antennas (LFD fallback @ 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

Digital signal processing1
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 don’t 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

  • Ntd beamformer
    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)

    Possible xntd correlator
    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

    Some influential milestones
    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

    Focal plane arrays for the new technology demonstrator

    Focal Plane Arrays for the New Technology Demonstrator

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

    Ntd fpa system
    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

    Focal field overlaid with array
    Focal field overlaid with array



    • 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

    800MHz 1.9° scan

    1800MHz 2.6° scan

    Basic fpa operation
    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

    Fpa size vs f d
    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

    Low noise operation with a wideband uncooled fpa
    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

    Ongoing efforts towards an ntf fpa
    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

    Ongoing efforts towards an ntf fpa 2
    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

    Ongoing efforts towards an ntf fpa 3
    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