BDT Radio – 2b – CMV 2009/10/09 Basic Detection Techniques 2b (2009/10/09): Focal Plane Arrays Case study: WSRT System overview Receiver and processing chain Scanning, weigths

BDT Radio – 2b – CMV 2009/10/09 Principle of Phased Array Feeds Aim is to provide adequate Field of View to enable large surveys with reflector telescopes Multiple feed horn systems have widely separated beams on the sky (depending on f/D) Multiple elements are combined into compound beams Radio Astronomy enters the CCD era!. compound beam FPA feed reflector

BDT Radio – 2b – CMV 2009/10/09 Driving requirements APERTIF 12 Westerbork dishes Frequency range1000 – 1750 MHz Survey speed improvement Including bandwidth20x Excluding bandwidth10x Sensitivity 0.7x MFFE (cooled,20Kelvin) (doubling of integration time)  = 75%, T sys = 55 K

BDT Radio – 2b – CMV 2009/10/09 Top level block diagram

BDT Radio – 2b – CMV 2009/10/09 Front-end Replaces the Multi Frequency Front-End Vivaldi Array LNA Low Noise Room temperature LNA Discrete components Only antenna + LNA in feedbox

BDT Radio – 2b – CMV 2009/10/09 T sys contributions (central beam)

BDT Radio – 2b – CMV 2009/10/09 Digital processing Functions: Sub-band filtering (0.78 MHz) Beamforming (37 beams, 384 subbands) Correlator (for calibration and weight determination) Implementation: Custom FPGA based (cost, power, size) Output data rate: 178 Gbps per dish 10GbE links to correlator UniBoard

BDT Radio – 2b – CMV 2009/10/09 RF calibration, objectives Stable compound beam patterns (<1% variation at half-power) System temperature measurement (± 0.5 K) Flux scale Relative phase between dishes

BDT Radio – 2b – CMV 2009/10/09 Survey speed improvement Single dish Ae/Tsys is 0.7 of MFFE Tsys 30K -> 55k; Aperture eff 55% -> 75% Bandwith is 2 times MFFE Dishes FoV improvement Bandwidth Noise line Noise cont SSpeed line SSpeed cont Current WSRT system MHz1111 APERTIF baseline MHz

BDT Radio – 2b – CMV 2009/10/09 APERTIF prototype 144 element Vivaldi array on 25m WSRT dish Tunable from 1000 to 1800 MHz 30 MHz instantaneous bandwidth 70 K T sys Data recording back-end Prototype

BDT Radio – 2b – CMV 2009/10/09 Field of view When sufficient compound beams are formed, a smooth sensitivity over the field of view can be obtained Field of view with MFFE

BDT Radio – 2b – CMV 2009/10/09 Measurement results Source Cassiopeia A 1420 MHz 56 elements per compound beam Sensitivity cuts Weights2D pattern

BDT Radio – 2b – CMV 2009/10/09 Single dish imaging Single dish, single pointing image!! M31 with APERTIF prototype 1 telescope, 1 pointing, 121 beams M31 with WSRT 14 telescopes, 163 pointings

BDT Radio – 2b – CMV 2009/10/09 M31 3x3 mosaic

BDT Radio – 2b – CMV 2009/10/09 FPA in an interferometer Measured fringes FPA beam – Horn 1420 MHz 144m baseline Source: 3C286 (14.8 Jy) Bandwidth: 20 MHz Horn FPA 0 m144 m288 m576 m X 

BDT Radio – 2b – CMV 2009/10/09 First interferometric FPA image