BDT Radio – 2a – CMV 2009/10/06 Basic Detection Techniques 2a (2009/10/06): Array antennas Theory: interferometry & synthesis arrays Introduction Optical interferometry, coding of phase Radio interferometry, aperture synthesis Briefly: calibration Theory: aperture arrays & phased array feeds Beamforming Basics Sparse & dense arrays

BDT Radio – 2a – CMV 2009/10/06

MIDI

BDT Radio – 2a – CMV 2009/10/06

1971

BDT Radio – 2a – CMV 2009/10/06 Correlatie functies

BDT Radio – 2a – CMV 2009/10/06 Spectra

BDT Radio – 2a – CMV 2009/10/06 Aperture synthesis (4 hours, 45 deg dec)

BDT Radio – 2a – CMV 2009/10/06 Less sample points

BDT Radio – 2a – CMV 2009/10/06 Splitting the dots

BDT Radio – 2a – CMV 2009/10/06 Dynamic Modelling

BDT Radio – 2a – CMV 2009/10/06 Ongecalibreerd beeld

BDT Radio – 2a – CMV 2009/10/06 Gecalibreerd beeld

BDT Radio – 2a – CMV 2009/10/06 Redundancy XX YY Amplitude on 2 identical baselines of about 400m at 60 MHz Fringes CasA stopped, CygA shows as oscillation

BDT Radio – 2a – CMV 2009/10/06 Dynamic Modelling Global Sky Model Environment Model Instrument Model Sensor Data “Predict” (simulated data) “Solve”

BDT Radio – 2a – CMV 2009/10/06

Connecting Europe …

BDT Radio – 2a – CMV 2009/10/06

Aperture arrays

BDT Radio – 2a – CMV 2009/10/06 System level Overview

BDT Radio – 2a – CMV 2009/10/06 Sparse & dense Definition: Dense array: element spacing < λ/2 Sparse array: element spacing > λ/2

BDT Radio – 2a – CMV 2009/10/06 Grating lobes

BDT Radio – 2a – CMV 2009/10/06 Element spacinig Criterion for maximum element spacing grating lobes at the horizon Example: an array scanning up to θ = 30° requires d < 0.53 λ to avoid grating lobes

BDT Radio – 2a – CMV 2009/10/06 Element configuration

BDT Radio – 2a – CMV 2009/10/06 Array patterns LOFAR Station beams

BDT Radio – 2a – CMV 2009/10/06 Effective area

BDT Radio – 2a – CMV 2009/10/06 Beamforming Ideally, time delays are required For practical reasons, phase shifters are used For a single frequency: same effect Offset frequencies result in beam squint (similar to scanning)

BDT Radio – 2a – CMV 2009/10/06 Effect of beamsquint

BDT Radio – 2a – CMV 2009/10/06 True time delay beamformer (photonic)

BDT Radio – 2a – CMV 2009/10/06 Polyphase Filter Digital Controls Buffer amplifiersSwitches for combining Output amplifier Pads for probing