name 1SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

SKA(DS) System Design Aspects:SKA(DS) System Design Aspects:building a systembuilding a system

Laurens Bakker

name 2SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

System modelSystem model

Distributed beamforming

Antenna LNARF tile

connectRF signaltransport

receiverDigital

connect2nd stage

processingData

transportAnalog

beamformer

Central beamforming

Antenna LNARF tile

connectRF signaltransport

receiverDigital

connect2nd stage

processingData

transportDigital

connect1st stage

processing

N N N N/16 * N/16

N N N N N N N

*Assumes 2 indep. Beams, 2 pol, FOV 250sq.degree at 1GHz (both beams)

name 3SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

System modelSystem model

Distributed beamforming

Antenna LNARF tile

connectRF signaltransport

receiverDigital

connect2nd stage

processingData

transportAnalog

beamformer

Central beamforming

Antenna LNARF tile

connectRF signaltransport

receiverDigital

connect2nd stage

processingData

transportDigital

connect1st stage

processing

N N N N/16 * N/16

N N N N N N N

Central beamforming closely resembles FPA architecture

name 4SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

Central beamformingCentral beamforming

• rather different RF architecture for distributed and central

• We can’t use the same front-end (cost) in both cases– Central resembles FPA to a certain extend

– Some numbers of FPA at ASTRON (APERTIF)

name 5SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

Central beamformingCentral beamforming

• rather different RF architecture for distributed and central

• We can’t use the same front-end (cost) in both cases– Central resembles FPA to a certain extend

– Some numbers of FPA at ASTRON (APERTIF)

name 6SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

APERTIF prototypeAPERTIF prototype 8 x 7 x 2 elements Vivaldi array

Dual polarisation

112 antenna elements

112 amplifiers

60 cables

60 receivers

Frequency range 1.0 – 1.7 GHz

Element separation: 10 cm (/2 @ 1.5 GHz)

30 MHz bandwidth (backend)

Data recording backend (6.7 s)

APERTIF prototype

name 7SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

Some APERTIF numbersSome APERTIF numbers

• It took about 2 days to assemble the antenna

• It took about 2 days to connect all amplifiers and power

• It took about 2 hours to connect the cables on both sides

• The front-end is ‘expensive’

• Voltage regulators ‘needed’ for performance (noise)

name 8SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

Some APERTIF numbersSome APERTIF numbers• It took about 2 days to assemble the antenna

• It took about 2 days to connect all amplifiers and power

• It took about 2 hours to connect the cables on both sides

• The front-end is ‘expensive’

• For AA:– Ease of deployment important

– Manufacturability important

• In general: getting a system operational takes a lot of time

name 9SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

System temperatureSystem temperature

• LNA noise temperature vs. Tsys

• Current APERTIF LNA is ~50K (with 15dB gain, 50 ohm)

• Current installed APERTIF front-end is ~65K (40dB gain, 50 ohm)

• Current measured Tsys ~115K

name 10SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

System temperatureSystem temperature

• LNA noise temperature vs. Tsys

• Current APERTIF LNA is ~50K (with 15dB gain, 50 ohm)

• Current installed APERTIF front-end is ~65K (40dB gain, 50 ohm)

• Current measured Tsys ~115K

• So Tsys about 65 K higher than LNA– 15K second stage front-end

– Feed loss and loss connectors ~20K (‘expensive’ RF material used)• Low cost high performance connectors needed (or no connectors at all)

– Noise coupling/mismatch about 10K (LNA has low Rn value)

– Sky noise 3K

– (spillover about 15K, not relevant for AA?)

name 11SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

System temperatureSystem temperature

• LNA noise temperature vs. Tsys

• Current APERTIF LNA is ~50K (with 15dB gain, 50 ohm)

• Current installed APERTIF front-end is ~67K (40dB gain, 50 ohm)

• Current measured Tsys ~115K

• So Tsys about 65 K higher than LNA– 15K second stage front-end

– Feed loss and loss connectors ~20K (‘expensive’ RF material used)

– Noise coupling/mismatch about 10K (LNA has low Rn value)

– Sky noise 3K

– (spillover about 15K, not relevant for AA)

• Quite some challenges ahead achieving Tsys numbers of (or even below) 50K as specified at low cost

name 12SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

Sky noise and survey speedSky noise and survey speed

• Sky noise rather dominant below 500 MHz

Tinst=40KEfficiency=75%A/T=10000

name 13SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

Sky noise and survey speedSky noise and survey speed

• Survey speed increases when scaled with 1/2

• A rather constant survey speed from 300-1GHz can be achieved with aperture array

Tinst=40KEfficiency=75%A/T=10000

name 14SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

Some SKA system Some SKA system optimizationoptimization points points

• Should optimize SKA system (and cost) as a whole– What should be the switchover frequency of AA ->dishes

– How many different antenna technologies are required to cover the whole band?

– 100-500MHz requires probably 2 different antenna types

– 500-800Mhz can easily be met with one antenna type• 300MHz-800MHz (or even 1000MHz) is also achievable

name 15SKA(DS) System Design Aspects4th SKADS Workshop, Lisbon, 2-3 October 2008

Some SKA system Some SKA system optimizationoptimization points points

• Should optimize SKA system (and cost) as a whole– What should be the switchover frequency of AA ->dishes

– How many different antenna technologies are required to cover the whole band?

– 100-500MHz requires probably 2 different antenna types

– 500-800Mhz can easily be met with one antenna type• 300MHz-800MHz (or even 1000MHz) is also achievable

• We should try to minimize the required number of different antenna types

• Running cost (esp. power consumption) should be taken in account early on in the design process