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Basic Detection Techniques

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

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Basic Detection Techniques

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  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

  2. MIDI

  3. 1971

  4. Correlatiefuncties

  5. Spectra

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

  7. Less sample points

  8. Splitting the dots

  9. Dynamic Modelling

  10. Ongecalibreerdbeeld

  11. Gecalibreerdbeeld

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

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

  14. Connecting Europe …

  15. Aperture arrays

  16. System level Overview

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

  18. Grating lobes

  19. 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

  20. Element configuration

  21. Array patterns • LOFAR Station beams

  22. Effective area

  23. 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)

  24. Effect of beamsquint

  25. True time delay beamformer (photonic)

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

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