DVP TestingNeil Roddis

Apr 15, 2010

SPDO

Why is test and verification so important for SKA dishes?

• Capital cost: design for low cost of a few thousand units – completely different to any previous purchase.

• Installation (cost and disruption): needs to be fast, involving few people with minimum tools and equipment.

• Maintenance (cost): we can’t afford frequent maintenance, e.g. greasing bearings.

• Power (cost): critical item for the SKA, much more so than on any previous project.

• Environment: bad.• EMC: much more demanding than usual because of

proximity of low frequency array.• IDR requirement: much more demanding than anything

before.2

SPDO• Risk reduction

– Verify as far as possible that dishes can be produced that when built up into the SKA system will meet all the science requirements.

• Inform design of the SKA antennas:– enable the greatest system sensitivity (Ae/Tsys and/or Survey

Speed) per unit system cost (total cost of ownership).– ensure that the contribution of antenna-related systematic

errors is within acceptable limits.– converge to a detailed design that is manufacturable in

production quantities and meets the other criteria on the previous slide

• Understand the costs: cost and performance are strongly related

DVP Testing

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SPDO

Approximate Verification Work Flow

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SPDO• Effective area vs frequency elevation angle• System noise temperature vs frequency and elevation

angle• Antenna radiation pattern vs frequency and elevation

angle• Sidelobe level stability vs frequency and elevation angle• Polarization discrimination• Pointing accuracy and stability

– Wind

– Solar radiation• (Imaging dynamic range)• EMC, including cross talk between closely adjacent

antennas

DVP Testing: What?

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SPDO• Noise: hot/cold load• Pointing: track strong sources• Surface accuracy:

– Satellite holography– Photogrammetry and/or laser tracker (over time)

• Polarization, pointing stability, sidelobe levels and stability:– Interferometry with reference antenna– Interferometry with reference array

DVP Testing: How?

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Potential Test Setup for SKA antenna

• Mosaic map pre-observed.• Calibrator:

o On-axis for the array.o Half-power point for SKA antenna.

Beam from SKA Antenna-Under-Test

Array Antenna Beam

Strong Calibrator

Field Source

Weak Field Source

Mosaicing Positions

SPDO• Acceptance tests

– Verify that it has been built to spec.– Photogrammetry, laser tracking etc.– Control system– Safety

• Stand-alone single dish tests– Start with a simple well-understood feed, progress to wide

band feeds and PAF– Deformation and pointing in wind and solar ilumination– Noise temperature– Stability tests– Use satellites and/or beacon(s)– Astronomical test limited by S/N

Antenna test sequence (1)

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Antenna test sequence (2)

• Single dish plus reference antenna or array– Enhanced S/N allows ‘deeper’ tests– Polarization– Stability: pointing and sidelobes

• Produce antenna system model– Pointing– Gain vs frequency and elevation– Noise vs frequency and elevation– Sidelobes vs frequency and elevation– Polarization vs frequency over wide field

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Antenna test resources

• Human: radio astronomy antenna integration and test expertise

• Site with infrastructure, preferably similar environment to candidate SKA sites

• Transmitter beacon: develop an antenna test range?• Satellite beacons? (small reference dish for holography)• Reference antenna? (as large as possible, covering wide

frequency range)• Reference array? (well-characterised, covering wide

frequency range)• Receiver sub system: very stable, covering the required

frequency range• Back end: including correlator

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