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Phased-Array Feed Measurements at Green Bank

Phased-Array Feed Measurements at Green Bank. Karl Warnick , Brian Jeffs Jonathan Landon, Mike Elmer Roger Norrod , Rick Fisher. R&D Challenges. Technical Mutual coupling Receiver/element noise Calibration Total bandwidth Cost Drivers Receiver system complexity Signal processing.

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Phased-Array Feed Measurements at Green Bank

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  1. Phased-Array Feed Measurements at Green Bank Karl Warnick, Brian Jeffs Jonathan Landon, Mike Elmer Roger Norrod, Rick Fisher

  2. R&D Challenges • Technical • Mutual coupling • Receiver/element noise • Calibration • Total bandwidth • Cost Drivers • Receiver system complexity • Signal processing

  3. 20-Meter Experiments • October 2007 • Tsys ~150K • July-August 2008 • LNA Ta = 30K, Tsys ~65K • Sky noise measurements • Direct Control of 20-m • ~1600 MHz, 0.5 MHz BW • 19 A/D samplers to disk • Software beam-forming

  4. Matching network G0 Mutual Coupling Effects • Changes element impedances • Beam-dependent • Couples amplifier noise • Changes element patterns • All frequency dependent

  5. Noise Budget MeasuredModel LNA Tmin33 K 33 K Noise coupling 20 K 23 K Spillover 5 K 5 K Sky 3 K 3 K Loss 4 K -- Tsys: 65 K 64 K Noise matching efficiency 60% Noise Matching Efficiency = 60% ---------- ----------

  6. Calibration • Optimize Ta/Tsys at each beam position in the FOV • Use strong radio source • R = cross-correlation matrix of all elements on and off source • w = beam-forming complex weights • λmax = highest eigenvalue corresponding to the dominant eigenvector of Roffw • Experience thus far is that calibration is stable for hours and possibly days in the experimental setup. • Calibration method does not distinguish between various noise and efficiency factors.

  7. Cygnus-X Region Mosaic Canadian Galactic Plane Survey Convolved to 20-m Beam

  8. RFI Cancellation with Array Processing

  9. Steps Toward a Cooled PFA

  10. Cool the Element Antennas? Polystyrene cover – low loss, low k, and strong enough, but outgassed heavily. Machined PTFE cover – low loss, moderate k, strong.

  11. Cool the Antenna Elements? So, PTFE vacuum cover is probably workable but concerns remain: Radiation loading, scattering, loss, robustness, interface with ground plane. Stress analysis Too thin cover after ~1mo under vacuum. PTFE creep.

  12. Noise Budget ~20cm

  13. Warm Antenna Elements?

  14. Test Facility Summer ‘08 New absorber in retractable roof, surveyed local obstacles and ground shield EM models for spillover estimation.

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