SKA Dishes, CSIRO 11-14 February 2013 SKA Dish Verification Antenna #1 Gary Hovey Astronomy...

SKA Dishes, CSIRO11-14 February 2013

SKA Dish Verification Antenna #1

Gary Hovey

Astronomy Technology Program – Penticton

12 February 2013


DVA1

Introduction

• Background/Motivation• Optics and Performance• Timeline• Remaining work

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DVA1

What SKA Needs

• Low cost per unit area of aperture. – low cost materials, low mass design, low fabrication labour

( favours symmetric )

• Very low operational cost for a 30 year life• Frequency range of 0.3 to 10+ GHz with suite of feeds

– ( favours offset )

• Excellent Ae / Tsys with low far out sidelobes– accurate surfaces, controlled spillover, low diffraction

( favours offset )

• Exceptional stability and dynamic range.– very rigid surfaces and very good pointing, over wind, gravity and

thermal (favours composites)

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DVA1

History

• Started investigating composite reflectors in 2005• Built Mk 1 in 2007• Built Mk 2 in 2008• Started collaborating with US-TDP in 2010 on building DVA1

• Concept Design Review done, February 2011• Preliminary Design Review done, October 2011• Detailed Design Review done, July 2012• Construction underway• Testing 2013/2014

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Dish Technology

From Richard Schilizzi


• Single piece reflectors often have low labour cost relative to alternate designs• A frame & spar system gives good edge & center support with an open center.• Wind & gravity moment loads are reduce with Az & El near the shell center.• The support system allows a compact turret head to be nested close to shell.• A compact turret head can contain almost all the precision machining needs.• A relatively simple pipe pedestal can support the turret head. ( wind &

thermal )

ATA Implementation

Matt Fleming, 2010-04-16 6 of 27


Optical Designs Considered

Matt Fleming, 2010-04-16 7 of 27


Dish Verification Antenna

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DVA1 Reflector

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Mount Components

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Design Goals

• Key aspects of the DVA-1 antenna– Extremely stable optical performance (dynamic range)– Rim-supported center-retained composite reflectors– Light-weight modular mount (off-site assembly)– “Mild” shaped offset-Gregorian feed-high optics (max A/T)– Large focal region capacity/flexibility– Platform for additional testing of feeds/electronics

• Focus has been on maximizing Performance/Cost while addressing manufacturability/maintainability

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Why a Composite Reflector? (and Not Metal Like the ATA)• Superior performance and cost competitive with metal

– Low thermal expansion materials.– Evolving material and manufacturing technologies– Large membrane surfaces possible.– Can tailor material to meet cost or performance requirement

• Highly accurate and stable surface– Over gravity, wind, and temperature.

• A stable and predictable radiation pattern.– Essential for high dynamic range imaging.

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EM Advantages of Offsets Reflectors

• Clear optical path, no blockage or scattering• Can support large sub-reflectors or feeds at the prime focus.• Combined with shaped optics, leads to very low spillover (~ -

50db wide angle)• Very low spillover yields very low antenna noise temperature

(<6 K ground)• Very low spillover results in high rejection of RFI and strong

sources• Shaped optics yield high efficiencies, total result is a high Aeff /

Tsys

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Practical Advantages of Offsets Reflectors

• Ample space and load capability to mount multiple feeds• Feeds, receivers and interchange mechanism out of optical

path• Access to payload area with out impacting either reflector• PAF can be mounted at either secondary or primary focal area• For structural cost reasons, DVA-1 is “feed arm high”• Easy, effective maintenance access with a standard scissors lift

truck

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DVA-1 Beam Pattern, Perfect Feed

Lynn Baker, US TDP, Cornell

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DVA-1 Low Frequency Performance.35 To 2.8 GHz.

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DVA-1 Efficiency, 3 Corrugated Horns

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15m Shaped Offset Gregorian DVA1Antenna Temperature vs. Elevation1.4 GHz

It uses the antenna pattern of the 55° elevation case, and it assumes that the antenna pattern remains the same for all elevation angles, as the gravitational deformation response at 1.4 GHz is undistinguishable from the undeformed surface case.

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15m Shaped Offset Gregorian DVA1Full Wide Far Field Pattern 1.4 GHzGravity Deformation @ Elev: 55°

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Gravity Distortion Worst Case @ Elev: 15°German Cortes, US-TDP, Cornell

Aperture Phase Distribution [λ]Aperture Power Distribution

-0.007 λ

-0.031 λ +0.0062 λ

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15m Shaped Offset Gregorian DVA1Beam Far Field Pattern + Gravity @ Elev: 15°

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DVA1

Gravity Errors at 18 GHz

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DVA1

Gravity, Wind, and Thermal Design Performance (1g, 25 kph, 25D C

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DVA1

Summary of Optics Design/Analysis

• The structure is essentially perfect at 1.4 GHz.• Antenna noise temperature is very low, 6K at zenith• Aperture Efficiency 80%• Aeff/Tsys is greater than 6 m^2 / K

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Dish Verification Antenna

• Gregorian Optics - optimised for maximum area and minimum noise (Aeff/Tsys)

• Cost effective but robust mount design

• Optimized feed support that is stiff, light, and low cost.• Simple and stiff backup structure.• Rim supported composite surface (accurate, stable, low labour)• Secondary focus provides large space for receivers• Primary focus can be used by a Phased Array Feed• Targeted to meet SKA specifications.

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DVA1

What’s next?

Summarize Results from DVA1• Performance and Costs.

Optimise and refine design for SKA1• Review requirements and finalize them.• Review and refine optics design.• Review mechanical design and tailor it for cost and

performance.• Optimize design for mass production.• Re-analyze cost for SKA2.• Build and demonstrate DVA2 a production prototype for SKA1.

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Questions? Comments?Help Welcome

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SKA Dishes, CSIRO 11-14 February 2013 SKA Dish Verification Antenna #1 Gary Hovey Astronomy...

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