Netherlands Institute for Radio Astronomy 1 ASTRON is part of the Netherlands Organisation for Scientific Research (NWO) From LOFAR design to SKA1 System André Gunst
2 Conclusions System Engineering Process Crucial for the SKA Non-astronomical requirements are even (more) important Twice the number of LBAs are used to cover 1.5 octave freq. range HBA hierarchical beamforming used to invest more in “area”
3 Reflection Questions, questions, questions … Should be structured and prioritized in the risk register Then they should be assigned and mitigated (or not) Without we will not answer the right questions in time
4 LOFAR Documentation Plan
5 Not only astro req.’s
6 SKA Requirements
7 Potsdam Juelich Tautenburg Garching Effelsberg Nancay Chilbolton Onsala Jena
8 Number and Size of Stations Total required sensitivity Minimum size required for station calibration Instantaneous imaging capability (snapshots) UV coverage in synthesis mode System costs Station electronics: ~ antennas * stations Network electronics: ~ stations Correlator: ~ stations 2 * beams Post processing: ~ stations 2 * beams * (B max /D s )*N ch Cost efficient to make FOV with multiple beams and smaller amount of stations
9 LOFAR station MHz MHz Optional 10- … MHz
10 Station “Backend” Electronics Shared in LOFAR over multiple arrays LBA optimized for MHz (original target MHz) Possibility for two configurations HBA optimized for MHz “LBL” usable from MHz
11 Central Systems Shared in LOFAR as well over the multiple arrays Can only observe one array at the same time For SKA thought should be given as well to share central systems for all AA arrays and the dishes
12 HBA Hierarchical Beamforming
13 HBA Mechanical Started with “eye catching spiders”
14 HBA Mechanical Ended with “boring boxes”
15 How Could That Happen … Because Needs a 15 year lifetime Needs to withstand storm, snow, sun load Needs to be assembled in the field efficiently Needs to have “zero cost” Industry was involved All non-astronomical requirements
16 HBA Assembly
17 Station Subrack
18 What if: the money is really limited … Money shortage leads to creativity
19 Creative Changes Dutch stations half as large Two LBA fields in Dutch stations (low cost penalty): LBA outer array LBA inner array Enabled by extra analog input in receiver HBA field of Core Stations split UV coverage improved Station calibration “deproved” Enabled by scalability of station hardware Number of output bits 16, 8 or 4 bit Exchange between bits for beams Enabled by usage of FPGAs
20 International Stations (≥ 8)
21 Remote Stations (16)
22 Core Stations (24)
23 Nancay Super Station Add an extra low band antenna array to the LOFAR station Uses the “third” receiver input 96 mini arrays Each array consists of ~ 10 antenna elements Optimized for < 30 MHz region
24 What SKA can use … AA low bandwidth: MHz (2.5 octave) One antenna type or two? Depends on Sensitivity profile over frequency Technology + cost Possibility as well to share backend electronics Keep doing system engineering Freeze requirements at System Requirements Review (latest) Everyone benefits: gives focus and clarity Track changes in requirements and analyze impact Changes can ripple through all layers of the system Change = money and sensitivity ~ money!
25 Conclusions System Engineering Process Crucial for the SKA Non-astronomical requirements are even (more) important Twice the number of LBAs are used to cover 1.5 octave freq. range HBA hierarchical beamforming used to invest more in “area”
26 The End