1. Phased Array Feeds Wim van Cappellen
ASTRON is part of the Netherlands Organisation for Scientific Research (NWO)

2. APERTIF: Phased Array Feeds for the WSRT
Transform the WSRT into an efficient 21-cm survey facility
17x Survey speed increase
SKA Pathfinder
Currently, the WSRT uses horn feeds with cryo receivers
APERTIF will provide a realistic reference point for the SKA PAF

3. APERTIF Science Two main surveys Unique synergy with LOFAR: And
Large-area imaging survey (continuum & spectral line)
Large-area transient survey
Unique synergy with LOFAR:
Good match in continuum sensitivity
and resolution
And
(Wide-field) VLBI
Pulsar timing …
Medium deep surveys of fields that overlap with other surveys
Shallow survey of the rest of the northern sky
one can study the spatial structure of the HI
distribution and of the kinematics, something that with the ASKAP is only possible to a limited extent
Although there are low-frequency facilities available/planned for the southern hemisphere, none of these,
including SKA1-low, have a spatial resolution matching that of the southern hemisphere L-band SKA
pathfinders. Therefore the combination Apertif-LOFAR is and will remain unique among SKA1 and the SKA
pathfinders.

4. APERTIF specifications
Frequency range – 1750 MHz
Instantaneous bandwidth 300 MHz
Channel bandwidth 12 kHz
Polarization Dual linear
Reflectors 12 x 25m
Baselines 36 to 2412 m
System temperature 70 K
Aperture efficiency 75%
Simultaneous beams 37 dual pol
Field of view 8 deg2
“Survey speed increase” 17x
Because there are 37 beams, we can survey the sky 37x times faster than the current system. But since the sensitivity of APERTIF is less than the MFFE, the survey speed figure of merit is “only” 17x higher.

5. Top level block diagram, imaging

6. Transient + VLBI backend

7. Feed array Gain ~40 dB LNA Tmin = 0.24 dB Skyworks SKY67151
121 Vivaldi elements, dual polarization. 121 pixel radio CCD
Note the ragged edge of the array, which will show-up in slide 19 as well (sensitivity over the field of view)
Gain ~40 dB LNA Tmin = 0.24 dB Skyworks SKY67151

9. RFI immunity High-pass filter between the antenna and LNA
System temperature penalty ~15 K
Measured IP2 products now > 70 dB below system noise
(well below RA.769)
APERTIF band
GSM
DVB-T
APERTIF is in a very hostile RFI environment. We had to install a filter (at room temperature) between the antenna and LNA. It works very adequately, but adds 15 to 20 K to the system noise.

10. APERTIF vs MFFE single-dish sensitivity
Lower, but MUCH smoother (good for calibration)
APERTIF is less sensitive, but much smoother
Metingen voor 3 LO settings over elkaar heen geplot (rode lijn, zie je bijna niet)
The MFFE shows strong fluctuations due to the standing wave between the main reflector and the focus cabin. These are eliminated by the PAF because a large flat plate is now replaced with a Vivaldi array.
APERTIF system CDR, Dwingeloo, 8 – 10 October 2014

11. APERTIF, first 37 beam images

12. APERTIF, first 37 beam images

13. Future PAF work at ASTRON
APERTIF commissioning and operation
SKA PAF consortium
Support 4 – 8 GHz cryogenic PAF development (UMan, INAF, Chalmers, ASTRON)
Cryo-cooled L-band PAF for Parkes (CSIRO)
Significant industry interest in PAFs
(5G, satellite, point-to-point comms,
low-cost multi-function radar)