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

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

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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

6

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!

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