15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 1

Baseline Optical Design

DVA-1 Project

Lynn Baker

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 2

Baseline Optical DesignBaseline Optical Design

• Offset, shaped dual reflectors, Gregorian subreflector

• 15 meter aperture diameter

• 55 degree feed opening angle ( f/D = .47 )

• Primary size: 15 X 18.26 meters ( 12 X 14.62 meters )

• Secondary size: 3.97 meters ( 3.51 meters )

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 3

Key Advantages Of Offset ReflectorsKey Advantages Of Offset Reflectors

• Clear optical path, no blockage or scattering

• Subreflector can be large (no blockage)1. Allows use of low gain (wide beam), broadband horns2. Provides better low frequency performance

• Large “real estate” to mount receiver systems

• Cost only modestly larger than symmetric designs

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 4

Key Advantages Of Shaped DesignsKey Advantages Of Shaped Designs

• Capture of feed pattern to low level (-16 db.)1. Improved efficiency from high energy capture2. Low edge illumination, low spillover

• Energy is mapped on the primary in selectable manner1. Achieves high aperture efficiency2 Mapping provides low edge illumination, low spillover

• These features combined provide:1. Very low wide angle sidelobes2. Very low antenna noise temperature3. Selectable near in sidelobe levels and efficiency

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 5

Baseline 15 meter designBaseline 15 meter design

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 6

Baseline 15 meter designBaseline 15 meter design

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 7

Features Of Shaping SoftwareFeatures Of Shaping Software

• Perfect circular symmetry in the ray mapping

• Almost straight spokes, perfect in symmetry plane

• Very low cross polarization, zero in symmetry plane

• Selectable mapping from feed elevation to aperture radius

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 8

PO Analysis, Gaussian FeedPO Analysis, Gaussian Feed

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 9

PO Analysis, Gaussian FeedPO Analysis, Gaussian Feed

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 10

Features Of PO AnalysisFeatures Of PO Analysis

• Very low wide angle sidelobes, <~ -50 db.

• High efficiency, ~ 80%

• Very low cross polarization, -34 db. peak, zero boresight

• Excellent circular symmetry in main beam and first sidelobe

• Caveat: results for perfect feed and reflectors

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 11

Options & Design ChoicesOptions & Design Choices

• Shaping provides a continuum of optics choices.1. The feed to aperture mapping is selectable.2. Options for efficiency, first sidelobe and other parameters

• A given primary can be mated with multiple subreflectors1. Provides options for different feed angles.2. Performance degradation is very small

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 12

Linear Mapping, 12 MeterLinear Mapping, 12 Meter

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 13

Designing For A New Feed AngleDesigning For A New Feed Angle

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 14

Accomodating PAF’sAccomodating PAF’s

• PAF probably located at prime focus / caustic

• Secondary focus might be possible for limited FOV

• Focal region fields somewhat similar

• Integrated energy ~3% different

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 15

Caustic Region Fields, Shaped DesignCaustic Region Fields, Shaped Design

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 16

Focal Region Fields, Equivalent ParabolaFocal Region Fields, Equivalent Parabola

15-16 April 2010 Lynn Baker DVA-1 Meeting at NSFLynn Baker DVA-1 Meeting at NSF 17

SummarySummary

• Offset, shaped optics provide high performance1. High performance antennas => Fewer antennas in array

• Wide range of selectable design parameters

• Low wide angle sidelobes provide many advantages1. Low antenna noise temperature2. High RFI immunity3. Enhanced “dynamic range”

• PAF performance potentially good, requires study.