From LOFAR design to SKA1 System
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Transcript of From LOFAR design to SKA1 System
1 ASTRON is part of the Netherlands Organisation for Scientific Research (NWO)
Netherlands Institute for Radio Astronomy
From LOFAR design to SKA1 System
André Gunst
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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”
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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
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S c ien c e Ap p lic a tio n sD o c u m en t
S c ien c e Us erR eq u ir em en ts
D o c u m en t
S y s tem R eq u ir em en tS p ec if ic a tio n
S y s tem Arc h itec tu r a lD es ig n D o c u m en t
S u b s y s temR eq u ir em en tS p ec if ic a tio n
S u b s y s temAr c h itec tu r a l
D es ig n D o c u m en tSp ec ify
C omp liance
O p er a tio n sP lan
I n ter f ac e C o n tr o lD o c u m en t
An aly s isR ep o r ts
P r o to ty p ed es ig n s
R ef er en c ed o c u m en ts
Bac k g r o u n dd o c u m en ts
S c ien c ec o n s o r tiu m
S y s tem D es ig n& E n g in eer in g
S D E /w o r k -p ac k ag es
W o r k p ac k ag es
E n g in eer in gr ep o r ts
S im u la tio n s ,an a ly s es , . . .
LOFAR Documentation Plan
5Not only astro
req.’s
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SKA Requirements
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Potsdam
Juelich Tautenburg
Garching
Effelsberg
Nancay
Chilbolton
Onsala
Jena
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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
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LOFAR station
120-240 MHz
30-80 MHz
Optional10- … MHz
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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
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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
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1..16delaystep
delaystep
1..16delaystep
delaystep
1..16delaystep
delaystep
Receiver Filterbank
Receiver Filterbank
Receiver Filterbank
Station Beams
HBA Hierarchical Beamforming
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HBA Mechanical
Started with “eye catching spiders”
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HBA Mechanical
Ended with “boring boxes”
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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
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HBA Assembly
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Station Subrack
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What if: the money is really limited …
Money shortage leads to creativity
http://artistempowerment.com
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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
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International Stations (≥ 8)
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Remote Stations (16)
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Core Stations (24)
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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
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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!
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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”
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The
End