Istituto di Radioastronomia INAF -Italy-

S. Montebugnoli, G. Bianchi, C. Bortolotti, A. Cattani,A. Cremonini, A. Maccaferri, F. Perini, M. Roma, J. Roda, P. Zacchiroli.

The planned re-instrumentation of the Northern Cross large array will quickly lead to a

1% SKA-A2 (300 - 700 MHz) demonstratorbased on cylindrical reflectors,

allowing to:

1. Investigate the use of cylindrical concentrators for SKA.

2. Investigate on Multibeaming, adaptive beamformingand RFIs mitigation algorithms, imaging of large FOV and handling of large array.

3. Obtain low risk, medium cost large SKA demonstrator (planned to be ready late 2007).

The planned re-instrumentation of the Northern Cross Northern Cross large arraylarge array will quickly lead to a

1% SKA-A2 (300 - 700 MHz) demonstratorbased on cylindrical reflectors,

allowing to:

1. Investigate the use of cylindrical concentrators for SKA.

2. Investigate on Multibeaming, adaptive beamformingand RFIs mitigation algorithms, imaging of large FOV and handling of large array.

3. Obtain low risk, medium cost large SKA demonstrator (planned to be ready late 2007).

14

A- BEST-1: A first single N/S cylindrical reflector test bed (4 Rx)- Ag=176 m2

- ready early 2005,- National funds allocated.

BEST-1 , 2 and 3 a modular SKA experimental prototype…

4 Receivers

BEST-1

BEST-2

B- BEST-2: A second test bed equipped by 8 N/S cylindric reflectors (32 Rx)- Ag= 1410 m2

- ready early 2006, - National funds allocated.

C- BEST-3: An almost 1% SKA-A2 demonstrator obtained with the re-engineering of 8000 m2, (Ag total= 30.000 m2)- ready late 2007 - Cost about ≤250 €/m2

(Geometrical area is considered)

BEST-3

FrontFront--EndEndG: ~63 dBOIP3: 33.5 dBmTsys : ~30 KCost: 25 € (electronic)

15 € (housing)

In order to increase the reliability andmaintainability the only “outdore” electronic is the LNA and the analog TX optical link…..

The Front End during the installation phase on the cylidricalconcentrator focal line.

LNAOptical link

BEST-1 construction

… low cost analog optical links are a crucial block for the SKA telescope…..

Planned cost: 500 €

This Optical link is a thesis of a student from the local College of Engineering (Bologna)

<0.1dBGain Flatness

+32.8dBmInput IP331dBNoise Figure

>30.9dBOutput Return Loss

>28.6dBInput Return Loss

-22.9dBGain

link optimised at408MHz @ 16MHz BW

-22.1dBGainmax

>+30dBmInput IP3<31.25dBNoise Figure

>24.2dBOutput Return Loss

>9.5dBInput Return Loss

-23.7dBGainmin

link (not optimised) in the 300-600MHz band

First observation of the transit of Cassiopea with BEST-1

1 Rx=¼ of cylinder

4 receivers=1 cylinder

5.6 deg.7.1 deg. (1.7 deg.)

Old Crosshardwaredetector &

chart recorderBEST-1

IF

Direct imaging of the FOV with BEST-1

4 (Multiplications / sample) / Rx2 (Sum / sample) / Rx2(NRx-1) (Sums / sample) / beam

Beam i

A/D A/D A/D A/D

3 Beams

1 2 4

Digital Multibeam-forming

3

BEST-1

FX CorrelatorF

DFT

Polyphase filterclock

N

1

DFT

Polyphase filterclock

N

1

DFT

clock

1

FPGA(DSP)

FPGA(DSP)

FPGA(DSP)

FPGA(DSP)

FPGA(DSP)

FPGA(DSP)

X

CORNER TURNER MEMORYCORNER TURNER MEMORYN

Frequency channelD.Rx

D.Rx

D.Rx

Ch-1……

Imaging:

AIPS (Imaging)

1 2 3 4

1234

1234

1 2 3 41 2

21

1024Sample

1024X XT

1 2 3 41234

1 2 3 41234

<X XT>

Correlationmatrix averageΣ

XF Correlator

Calibration

CORRELATORX XT

AD

DDC

AD

DDC

AD

DDC

AD

DDC

LO

Sync.

r1 +j i1 r2+ji2 r3 +j i3 r4 +j i4

AdaptiveBeamformer

AdaptiveBeamformer

SVD (RFI DOA) d1(θ1), d2(θ2)…..

AdaptiveBeamformer

Multibeaming

W=R-1 d0(θ0)

d0H (θ0) R-1 d0(θ1) d0(θ0)

Radiosource(tracking)

yn=X(n) W*(n)

Imaging:

Best-1 (and the following Best-2 & 3) will play an important role in the simulation of the “real-life” of the next generation very largeradiotelescopes

1- ItIt willwill investigate investigate manymany aspectsaspects of theof the ArchitectureArchitecture of of largelarge arrayarray::- Achromatic Adaptive Beamforming: large demonstrator introduces high delays. Low cost precise digital delay banks are required to properly form

a certain amount of wide band adaptive beams. - Facing the design and the handling of large array infrastructures.- Design of XF and/or FX correlators.- Wide band optical fibre (analog)- RFI handling in a large array.- Reliabilty and Risk analysis evaluation exercise for large radiotelescope.

2- VerifyVerify thethe conceptsconcepts relatedrelated withwith the the mechanicalmechanical constructionconstruction of aof alargelarge array witharray with cylindercylinder reflectorsreflectors

3- AnAn almostalmost complete complete instantaneousinstantaneous uu--v v coveragecoverage SKA SKA largelargedemonstratordemonstrator..

4- A A largelarge demonstratordemonstrator (8.000 m(8.000 m22) ) ableable toto quicklyquickly generate generate sciencescience