BDT Radio – 2a – CMV 2009/10/06

Basic Detection Techniques

2a (2009/10/06): Array antennasTheory: interferometry & synthesis arrays

Introduction

Optical interferometry, coding of phase

Radio interferometry, aperture synthesis

Briefly: calibration

Theory: aperture arrays & phased array feedsBeamforming Basics

Sparse & 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/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 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