From LOFAR design to SKA1 System

1. From LOFAR design to SKA1 System André Gunst ASTRON is part of the Netherlands Organisation for Scientific Research (NWO)

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. Onsala Potsdam Jena Juelich Chilbolton Tautenburg Effelsberg Garching Nancay

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: ~ stations2 * beams • Post processing: ~ stations2 * beams * (Bmax/Ds)*Nch • Cost efficient to make FOV with multiple beams and smaller amount of stations

9. Optional 10- … MHz 30-80 MHz LOFAR station 120-240 MHz

10. Station “Backend” Electronics • Shared in LOFAR over multiple arrays • LBA optimized for 30-80 MHz (original target 10-80 MHz) • Possibility for two configurations • HBA optimized for 120-240 MHz • “LBL” usable from 10-80 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 http://artistempowerment.com

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: 70 - 450 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