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SKA(DS) System Design Aspects: building a system

SKA(DS) System Design Aspects: building a system. Laurens Bakker. System model. Distributed beamforming. N/16 *. N/16. N. N. N. Central beamforming. N. N. N. N. N. N. N. *Assumes 2 indep. Beams, 2 pol, FOV 250sq.degree at 1GHz (both beams). System model.

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SKA(DS) System Design Aspects: building a system

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  1. SKA(DS) System Design Aspects:building a system Laurens Bakker

  2. System model Distributed beamforming N/16 * N/16 N N N Central beamforming N N N N N N N *Assumes 2 indep. Beams, 2 pol, FOV 250sq.degree at 1GHz (both beams)

  3. System model Distributed beamforming N/16 * N/16 N N N Central beamforming N N N N N N N Central beamforming closely resembles FPA architecture

  4. Central 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)

  5. Central 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)

  6. APERTIF 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 (l/2 @ 1.5 GHz) 30 MHz bandwidth (backend) Data recording backend (6.7 s) APERTIF prototype

  7. Some 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)

  8. Some 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

  9. System 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

  10. System 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?)

  11. System 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

  12. Sky noise and survey speed • Sky noise rather dominant below 500 MHz Tinst=40K Efficiency=75% A/T=10000

  13. Sky 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=40K Efficiency=75% A/T=10000

  14. Some SKA system optimization 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

  15. Some SKA system optimization 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

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