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. Mutual Coupling Effects Changes element impedances – Beam-dependent Couples amplifier noise Changes element patterns All frequency dependent Matching network 00

5. Noise Budget Measured Model LNA T min 33 K 33 K Noise coupling20 K 23 K Spillover 5 K 5 K Sky 3 K 3 K Loss 4 K -- T sys :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 – λ max = highest eigenvalue corresponding to the dominant eigenvector of R off w 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 May 20099

10. Cool the Element Antennas? May 200910 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? May 200911 So, PTFE vacuum cover is probably workable but concerns remain: Radiation loading, scattering, loss, robustness, interface with ground plane. Too thin cover after ~1mo under vacuum. PTFE creep. Stress analysis

12. Noise Budget ~20cm ItemNoiseComment MW Background3 K Atm1 LNA4Balanced @ 15K Spillover/Scatter3-6Antenna dependent Subtotal11-14 KWe’re stuck with this! Array Noise3-6 ?Mutual coupling effects Input Losses3-6 ?Ohmic to LNA input Total17-26 K May 200912

13. Warm Antenna Elements? May 200913 ItemLossTempNoise Dipole Post0.02 dB300 K1.4 K Hermetic Bead0.073004.9 !! SS Coax0.091503.1 SMA Conn0.02150.1 Subtotal9.5 K

14. Test Facility May 200914 New absorber in retractable roof, surveyed local obstacles and ground shield EM models for spillover estimation. Summer ‘08