1. name1 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 SKA(DS) System Design Aspects: building a system Laurens Bakker

2. name2 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 System model Distributed beamforming Central beamforming NNN N/16 * N/16 NNNNNNN *Assumes 2 indep. Beams, 2 pol, FOV 250sq.degree at 1GHz (both beams)

3. name3 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 System model Distributed beamforming Central beamforming NNN N/16 * N/16 NNNNNNN Central beamforming closely resembles FPA architecture

4. name4 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 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. name5 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 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. name6 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 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 ( /2 @ 1.5 GHz) 30 MHz bandwidth (backend) Data recording backend (6.7 s) APERTIF prototype

7. name7 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 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. name8 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 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. name9 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 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. name10 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 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. name11 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 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. name12 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Sky noise and survey speed Sky noise rather dominant below 500 MHz Tinst=40K Efficiency=75% A/T=10000

13. name13 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 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. name14 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 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. name15 SKA(DS) System Design Aspects 4 th SKADS Workshop, Lisbon, 2-3 October 2008 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