Baseline Optical Design DVA-1 Project Lynn Baker

Baseline Optical Design DVA-1 Project Lynn Baker Lynn Baker DVA-1 Meeting at NSF

Baseline 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 ) Lynn Baker DVA-1 Meeting at NSF

Key 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 Lynn Baker DVA-1 Meeting at NSF

Key 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 Lynn Baker DVA-1 Meeting at NSF

Baseline 15 meter design Lynn Baker DVA-1 Meeting at NSF

Features 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 Lynn Baker DVA-1 Meeting at NSF

PO Analysis, Gaussian Feed Lynn Baker DVA-1 Meeting at NSF

Features 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 Lynn Baker DVA-1 Meeting at NSF

Options & 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 Lynn Baker DVA-1 Meeting at NSF

Linear Mapping, 12 Meter Lynn Baker DVA-1 Meeting at NSF

Designing For A New Feed Angle Lynn Baker DVA-1 Meeting at NSF

Accomodating 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 Lynn Baker DVA-1 Meeting at NSF

Caustic Region Fields, Shaped Design Lynn Baker DVA-1 Meeting at NSF

Focal Region Fields, Equivalent Parabola Lynn Baker DVA-1 Meeting at NSF

Summary • 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. Lynn Baker DVA-1 Meeting at NSF

Baseline Optical Design DVA-1 Project Lynn Baker