BDT Radio – 2a – CMV 2009/10/06
Basic Detection Techniques
2a (2009/10/06): Array antennasTheory: interferometry & synthesis arrays
IntroductionOptical interferometry, coding of phaseRadio interferometry, aperture synthesisBriefly: calibration
Theory: aperture arrays & phased array feedsBeamforming BasicsSparse & dense arrays
BDT Radio – 2a – CMV 2009/10/06
BDT Radio – 2a – CMV 2009/10/06
BDT Radio – 2a – CMV 2009/10/06
BDT Radio – 2a – CMV 2009/10/06
BDT Radio – 2a – CMV 2009/10/06
MIDI
BDT Radio – 2a – CMV 2009/10/06
BDT Radio – 2a – CMV 2009/10/06
1971
BDT Radio – 2a – CMV 2009/10/06
Correlatiefuncties
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
Ongecalibreerdbeeld
BDT Radio – 2a – CMV 2009/10/06
Gecalibreerdbeeld
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
BDT Radio – 2a – CMV 2009/10/06
Connecting Europe …
BDT Radio – 2a – CMV 2009/10/06
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/2Sparse 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 requiredFor practical reasons, phase shifters are used
For a single frequency: same effectOffset 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 amplifiers Switches for combining
Output amplifier
Pads for probing
