Basic Detection Techniques

1. 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

6. MIDI

8. 1971

9. Correlatiefuncties

10. Spectra

11. Aperture synthesis (4 hours, 45 deg dec)

12. Less sample points

13. Splitting the dots

14. Dynamic Modelling

15. Ongecalibreerdbeeld

16. Gecalibreerdbeeld

17. Redundancy Amplitude on 2 identical baselines of about 400m at 60 MHz Fringes CasA stopped, CygA shows as oscillation XX YY

18. Dynamic Modelling Global Sky Model Environment Model Instrument Model “Predict” (simulated data) “Solve” Sensor Data

20. Connecting Europe …

22. Aperture arrays

23. System level Overview

24. Sparse & dense • Definition: • Dense array: element spacing < λ/2 • Sparse array: element spacing > λ/2

25. Grating lobes

26. 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

27. Element configuration

28. Array patterns • LOFAR Station beams

29. Effective area

30. 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)

31. Effect of beamsquint

32. True time delay beamformer (photonic)

33. Digital Controls Output amplifier Buffer amplifiers Switches for combining Polyphase Filter Pads for probing