May AA Communications. Portugal

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2 SKA Top-level description A large radio telescope for transformational science Up to 1 million m 2 collecting area Operating from 70 MHz to 10 GHz (4m-3cm) Two or more detector technologies Connected to a signal processor and high performance computing system by an optical fibre network Providing 40 x sensitivity of the EVLA, and up to 100,000 x survey speed

3 SKA 1 Receptor Technologies ~250 Dishes One Core reserved for SKA 2 use. 2-Core Central Region AA-low - 50 arrays Artists Renditions from Swinburne Astronomy Productions

4 SKA 2 Receptor Technologies 250 Dense Aperture Arrays Dishes 3-Core Central Region AA-low Arrays Artist renditions from Swinburne Astronomy Productions

5 Aperture Arrays Michael Kramer

6 Sparse or Dense. Dense: Element spacing λ/2 Fully sampled wavefront Regular layout pattern Constant A eff Excellent side lobe control Beam performance equiv to the best dish design Sparse: Element spacing >λ/2 A eff increases as λ 2 (~ λ 2 /4) Layout irregular to control grating lobes Increased skynoise from grating lobes Possible dynamic range issues

7 Sky Temperature, T sky, K Sparse and Dense regimes Sky Noise Temperature Sky dominated noise Receiver dominated noise ,000 1,200 1,400 1,600 1,800 2,000 Frequency MHz

8 Why aperture arrays? At low frequencies, <~300MHz, the only realistic way of building sufficient collecting area Unsurpassed ability to create Field of View through multiple beams Extremely flexible in observational parameters e.g. Sky area vs. bandwidth Can run multiple experiments concurrently Using a large amount of up front processing they reduce the backend processing load Can tune imaging coverage, beam size, post-processing load etc. ICT based AAs provide many new opportunities

9 An SKA collector summary SKA 1 Freq. Range Collector Sensitivity Number / size Distribution 70 MHz to 450 MHz 300 MHz to 3 GHz AA-low Sparse AA Dishes with single pixel feed 1,000 m 2 /K at 100 MHz 1,000 m 2 /K at 1.4 GHz 50 arrays, Diameter 180 m 70% within 5 km dia., 250 dishes Diameter 15 m 30 % along 3 spiral arms out to 100 km radius SKA 2 Freq. Range Collector Sensitivity Number / size Distribution 70 MHz to 450 MHz 400 MHz to 1.45 GHz 300/1000 MHz to 10 GHz AA-low Sparse AA AA-mid Dense AA Dishes with single pixel feed + PAF 4,000 m 2 /K at 100 MHz 10,000 m 2 /K at 800 MHz 10,000 m 2 /K at 1.4 GHz 250 arrays, Diameter 180 m 250 arrays, Diameter 56 m dishes Diameter 15 m 66% within 5 km dia., 34% along 5 spiral arms out to 180 km radius 50% within 5 km dia, 30% 5km km 20% 180 km-3,000 km.

10 SKA 2 wide area data flow GHz Wide FoV MHz Wide FoV GHz WB-Single Pixel feeds Dense AA.... Sparse AA Aperture Array Station Tile & Station Processing DSP... Central Processing Facility - CPF 16 Tb/s To 250 AA Stations 4 Pb/s Correlator UV s Image formation Archive Data Time Control 20 Gb/s 16 Tb/s Optical Data links AA slice AA slice... Dish & AA+Dish Correlation AA slice 24 Pb/s Tb/s Data switch... Imaging s Tb/s Gb/s Gb/s Control s & User interface Data Archive Science s 15m Dishes DSP Gb/s... Time Standard To 1200 Dishes User interface via Internet

11 Survey speed Fixed Simple survey speed: Survey speed w/bw: ( A eff /T) 2 Ω ( A eff /T) 2 ΩΔν Critical for the SKA a discovery instrument Station data rate, DR st : N beams Ω Δν Total data rate, Dr tot : For fixed Aeff N stn * DR stn Station dia. D (N stn ) -0.5 & Ω stn D -2 Hence A eff Effective collecting area, m 2 T System temperature, K Ω Field of View. deg 2 Δν Bandwidth, Hz Total data rate for a fixed survey speed is independent of # of stations (fixed A eff & Bandwidth)

12 LOFAR

13 AA-low element development Toothed logperiodic antennas for pattern improvement BLU antenna: Bow-tie Low Freq. Ultra-Wideband antenna Pattern measure

14 AA-low elements & array

15 LWA element: mechanical example Electronics at top well away from floods etc. Simple skeleton elements (delivered flat) Clamp type rotational adjustment Single pole fixing just sunk into ground Buried cables Easy and quick deployment Cheap mesh groundplane

16 AA-mid Array

17 AA-mid elements and array ORA array - SKADS Vivaldi array - EMBRACE Dense array design, largely decided, select: Element pitch for frequency range & element type Element type and construction technique LNA: differential or single ended

18 TH_n Comms in generic AA with 2-stage beamforming Ae Ae Ae 1.4GHz analogue TH_1 TH_0 Tile - hi Tile - lo 12 fibre each Station Typical: AA-hi tiles: 300 AA-lo tiles: 45 Total: 345 I/p data rate: 42Tb/s 12 fibre each Long distance drivers Long distance drivers e/ oe/ oe/ oe/ o 10Gb/s fibre To Correlator 0.5 GHz analogue TL_0 TL_1 TL_m Max 4 Station s Distributed to all processors in the Station Station control processors Station n To Central control systems Local Processing e.g. Cal; pulsars Long distance drivers..

19 Cooling 2-Pol Elements... Copper Element Digitisation Fibre Element Digitisation Tile Digitisation Tile RFI Digitisation Shielded Element Data C & M Station Processing RFI shielded Station Beams Control & Monitoring... 2x 500MHz Analogue + power Front-end Conventional AA-low Station Clock Element Digitisation... Power Distribution System clock To Correlator & Services Power Grid

20 Delay 1-D Beamforming Incoming signal Array width Elements t Beam Electronic Delay 0 Element #

21 Two stage beamforming Station beams Central perfect beam Tile beam Filling Tile beams with station beams leads to discontinuities in the beamforming for off-centre beams Incoming signal Elements Electronic Delay Tiles Station processor Beam Can be resolved with higher data rate Tile to Station tdelay Tile Beam 0 Element #

22 6 x 120Gb/s 6 x 120Gb/s To Element Digitisation Each link is 12 fibre lanes@10gb/s Station processor Primary Station Board 0 Primary Station Board 1.. Primary Station Board (max 35) Each link is 12 fibre lanes@10gb/s Station All to All Connections Hierarchical structure: Linked with comms Secondary Station Board 0 Secondary Station Board 1.. Secondary Station Board (max 35) Long distance drivers Long distance drivers Long distance drivers Optical links To Correlator 12-channel Rx module. e.g Avago AFBR-820BXXZ To Element digitisation or Primary Station s Each link is 12 fibre lanes@10gb/s Total Raw input data rate: 4.32Tb/s Requirements: High bandwidth in High bandwidth out Largely cross connected Scaleable at various levels Programmable beamforming PChip PChip PChip PChip PChip PChip Each link is 12 diff. copper lanes@10gb/s All to All Connections PChip PChip PChip PChip PChip PChip PChip 20 TMAC Control Line Tx/Rx 12-channel Tx module. e.g Avago AFBR-810BXXZ To Secondary Station s or long distance fibre drivers Each link is 12 fibre lanes@10gb/s Total Raw output data rate: 4.32Tb/s max Station Control

23 Output data rate & array performance The output data rate defines the performance of the array A better measure than beams since it considers flexible use of data between bandwidth and direction. Front end analogue beamforming restricts areas of sky that can be observed concurrently Changing the number of bits/sample for different observation types maximises performance Not a problem for the correlator which only sees total data rate Post-processor needs to interpret blocks of data Build flexibility into the Station processor

24 Potential AA-low station design 1. There are 11,264 dual polarisation elements in a station; 2. Station diameter is 180m; 3. There is no analogue beamforming, every element is digitised; 4. The digitisation is in 44 Tiles of 256 elements each; 5. Data rate off each digitisation box set at 240Gb/s, after some beamforming; 6. The full active bandwidth from the digitisers is returned to the central processor; 7. A station has 22,400 digital receiver channels.

25 AA-low station signal path Element assembly Digitisation box Station Processing Antenna LNA Gain Block ADC comms Analog conditioning ADC Digitisation Processing Primary Station Processing Secondary Station Processing To Correlator Control Signal Transport Clock Distribution Tile station processor optical comms optical interconnect Wide area optical comms Copper: ~20m, 500MHz Optical: ~200m, 10Gb/s Optical: <20m, 120Gb/s

26 Standalone SKA-low element (option) Elements: MHz Solar panel ADC: 1GS/s Power conditioning Processing m all optical Data Control Energy storage Analogue Sync. Benefits: Integrated single unit No copper connection Easy to deploy Minimum RFI Lightning immunity Challenges: Low total power Integration Manufacturability Packaging No need for digitisation boxes

27 Cooling Stand-alone Elements Self powered element Fibre Station Beams Element Data C & M Clock... Station Processing RFI shielded Control & Monitoring System clock Advanced AA-low Station Single or multiple fibres To Correlator & Services Power Grid

28 AA-mid station design: SKA 2 1. The element pitch is 15 cm (λ/2 at 1GHz); 2. Station diameter is 56m, or ~2500m 2 ; 3. Analogue beamform 4 elements; 4. Tiles are 16x16 dual polarisation elements (2.4m square); 5. Tiles have 128 digitisation channels (256*2/4); 6. Data rate off each Tile set at 120Gb/s 7. A Station has 430 Tiles or 110,000 elements or 220,000 receiver chains. 8. A station has 55,000 digital receiver channels.

29 AA-mid proposed signal path Tile TTD 4-element clusters Tile processing unit Front-end Tile Processing Station Processing Antenna LNA Gain Block Analog Cond. ADC comms RF Beamforming ADC Tile Digital Processing Primary Station Processing Secondary Station Processing To Correlator Tile Local Tile Analogue Signal Transport Clock Distribution optical interconnect Wide area optical comms Tile Element & gain. Phantom power Tile station processor optical comms

30 Summary Comms speed is critical at all levels of the AA system Overall requires multi-km, 100 s m, & 10 s m range comms AAs depend on high speed comms and processing More communications gives more performance Increasing comms rate and more processing is a clear upgrade path AA-mid is very challenging.