Focal Plane Array Related Activities at CSIRO

Transcription

1 ICT Centre /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 Australia

2 Outline of Presentation Past experience with focal plane arrays CSIRO and other activities related to FPAs Antennas SKA proposals FPAs Line feeds Integrated receiver systems High-speed digital correlators What CSIRO brings to collaboration with Europe Design Measurement

3 Parkes Multibeam Receiver System Multibeam receiver system sits in the telescope s focus cabin and receives signals from space Telescope sees 13 patches of sky simultaneously Radio signals from galaxies in space hit surface of telescope and are reflected to focus cabin Telescope detects faint galaxies (Data for the Southern sky)

4 Arecibo Multibeam Feed System Successfully installed in April 2004 Feed array ( GHz) under test at CSIRO Arecibo radio telescope

5 Arecibo Multibeam Feed Array Sample Results Element 3 : Array reference 45, OMT horizontal plane at GHz & distance 3.7m 3 Theory Theory

6 Current Australian Radio Astronomy Projects with FPAs FARADAY and PHAROS MUDDA multi-use dense digital array Australian 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

7 Antennas

8 SKA Configurations Technical and cost assessments Luneburg lens Cylindrical reflector Wide-field of view (WFOV) reflector Luneburg lens Cylindrical reflector WFOV reflector

9 Prototype Luneburg Lens Construction

10 Measurement of Prototype Luneburg Lens Aperture field Far field Measured results in S-band

11 Luneburg Lens with Egg-crate FPA The ASTRON FARADAY FPA we had on site was used as an illuminator for the Konkur lens.

12 Cylindrical Reflector Offset-fed options Improved cost model Wideband line-feed development (with Sydney Uni.)

13 WFOV Reflector FOV ~10º x 10º ~14m diameter reflector Large array in focal region Array is extendable Technology is well developed and cost known Three CSIRO MultiBeam antennas at SES-ASTRA, Luxembourg. Each antenna covers a ~40º x 1º FOV.

14 Focal-plane Arrays All SKA are expected to use focal-plane arrays Focal-plane arrays: Allow formation of multiple beams Correct for errors in reflectors or lenses Allow electronic beam scanning Prototype focal plane array of Vivaldi elements

15 Approach to Focal Plane Feeds Compact feed elements Close packing (max. spacing < 0.9λ) Wideband Dual polarization Rigorous analysis including mutual coupling Excitation chosen to maximize secondary antenna A eff /T (G/T)

16 Focal Plane Feed Options Single feed per beam Array cluster per beam

17 Cluster Feed Approach Choose array excitation to maximize G/T A Overlap sub-arrays trade-off between number of elements and efficiency Combine signals at: RF IF M x N processor

18 Overlapping Sub-arrays Example: 3 overlapping hexagonal arrays Efficiency improvement is terraced, for example: Beam efficiency % No. of Elements

19 Array Excitation for Maximum G/T A Antenna gain Q(θ,φ) * Q(θ,φ) (cx) (c x) G(θ,φ) = G o = G o P f x x c = correlation coefficients between the focal field and co-polar modes in the apertures x = normalized array excitation coefficient vector Note: Gain is maximum when x = c. Zero cross-polarization in beam direction when x = c d c dd d where d is similar to c except for cross-polar modes Antenna temperature T A = 1 x G(θ,φ)T(θ,φ) 4π B x dω=g o Ω x x For a given beam direction (θ,φ), G/T A is maximum when x = B 1 c Mutual coupling between feed elements is included.

20 Potential Elements for Close Packed Arrays Coaxial waveguide (b/a>0.4) Dielectric rod Microstrip patch b a Helical (Qassim & McEwan) Travelling-wave slot antennas Vivaldi ~0.25λ top patch driven patch x choke ring y Balanced Anti-podal input probe ground plane ~0.8λ (after Kiskh & Shafai) y y=±aexp(rx) A x truncation limits - A

21 Arrays of Coaxial Horns X -20 Mode matching method for coaxial horns Accurate mutual coupling analysis (Bird, Trans. IEEE, Mar. 2004, pp ) In compact arrays 1 a < π(1 + (b/a)) < λ s 2 Y E 2 E Validation of analysis Low-loss polystyrene foam spacers Coupling coefficient db S12 (theory) S13 (theory) S12 (expt) S13 (expt) Frequency GHz X where s is the element spacing in wavelengths < 0.9 Example: s < λ/2, b/a > Y Irises All dimensions in mm Feed element for Jodrell Bank Lovell radio telescope

22 Balanced Anti-podal Vivaldi Antenna E-plane H-plane With dielectric Without dielectric Computations by S. Hanham, CSIRO With CST Microwave Studio Cross-polarization is high

23 Surface Currents on Vivaldi Elements Conventional balanced Vivaldi Crossed balanced Vivaldi

24 Integrated Receiver Systems

25 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 MHz (nom). T sys < 50K (uncooled). Instantaneous IF bandwidth 500 MHz. ~40dB (6 8 bits) dynamic range. Dimensions 1.5m x 1.5m.

26 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

27 Possible Block Diagram

28 Radio on a Chip Takes advantage of low cost, low power RF- CMOS processes developed for wireless networking Will 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.

29 High-speed Digital Correlators

30 2 GHz Bandwidth Correlator with Polyphase Filterbank 2GHz 2GHz 4k channels Basic Configuration 2GHz 4k channels 4k channels 4k channels Multiple Zoom (>2 possible) Simple Zoom 2GHz xn x 0 (m) x 1 (m) xρ(m) x M-1 (m) po(m) p1(m) pρ(m) pm-1(m) X0(m) 0 X1(m) 1 M-Point ρ M-Point DFT DFT Via via FFT M-1 Xk(m) (m) XM-1 DMUX FIR FFT FIR FFT Filterbank Fringe Rotators Correlators FPGA hardware may be completely reprogrammed to produce many different filterbank configurations, as different observations may require. 4k channels 4k channels Compound Zoom A 2GHz bandwidth polyphase digital filterbank with 4096 channels will fit into four XC2V6000 FPGAs

31 Wideband Correlation Build wider bandwidths by paralleling 2GHz slices 8 GHz (per polarisation) high resolution spectrometer for MOPRA 2GHz bandwidth per IF, four IFs per antenna

32 Baseband Receiver / PoC Spectrometer 1024 Channel Spectrum, DC-256MHz

33 Molonglo Observatory Synthesis Telescope Material supplied by Anne Green, University of Sydney Photo: G. Warr

34 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 Telescope Joint venture between University of Sydney and CSIRO

35 SKAMP Science Goals Low-frequency radio spectrometry ( 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 ( 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 deg 2 accessible around main beam. Real time de-dispersion

36 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 GHz >100 MHz instant BW Cylindrical antenna prototype RFI mitigation strategies - adaptive noise cancellation

37 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

38 Petal Line Feed Element 0-5 Measured Azimuth Patterns for Antenna Prototype, F=1539MHz Co-polar X-po la r B ) (d d e p l itu m A Element pattern θ (degrees )

39 SKA New Technology Demonstrator (NTD) Aims: Antenna, receiver and backend technology for support wide FOV, wideband astronomy Operational 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 provision Environmental conditioning on a semi-arid remote site

40 Concluding Remarks Overview of projects in progress Antennas Integrated receivers High-speed digital correlators Demonstrators in progress Keen to continue collaboration with Europe through PHAROS etc