L. Kogan , F. Owen , J. Ott , A. Cohen National Radio Astronomy Observatory Socorro, NM USA

Optimization of Compact Array Configurations to Minimize Side-Lobes for Two Cases:

The New E-configuration for the EVLA andThe LWA Phased-array Station

L. Kogan , F. Owen , J. Ott , A. CohenNational Radio Astronomy Observatory Socorro, NM USA

The Johns Hopkins University, Applied Physics Laboratory

217th AAS Meeting-Seattle,WA217th AAS Meeting-Seattle,WA

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January 13, 2011January 13, 2011


Configuration figures of meritConfiguration figures of merit……

• Minimum side lobesMinimum side lobes• Gaussian shape of the main beamGaussian shape of the main beam• Minimum gaps in the UV coverageMinimum gaps in the UV coverage• OthersOthers

Optimizing figures of merit other than “Minimum side lobes” improves the side lobes Optimizing figures of merit other than “Minimum side lobes” improves the side lobes implicitly, but the direct minimum side lobe optimization may produce better result. implicitly, but the direct minimum side lobe optimization may produce better result.

We optimize the array configuration minimizing the maximum positive side We optimize the array configuration minimizing the maximum positive side lobe inside of the primary beam!lobe inside of the primary beam!

Kogan 2000, IEEE Transaction on Antennas and Propagation, 48, 7, 1075Kogan 2000, IEEE Transaction on Antennas and Propagation, 48, 7, 1075

The algorithm is coded in AIPS as task CONFIThe algorithm is coded in AIPS as task CONFI

The achieved small side lobes for the considered arrays promise high image The achieved small side lobes for the considered arrays promise high image fidelity for maximum scientific results!!!fidelity for maximum scientific results!!!



Left: Mathematically created mask to prevent appearance of antennas (during optimization) on the prohibited places: Left: Mathematically created mask to prevent appearance of antennas (during optimization) on the prohibited places: proximity to tracks, proximity to fixed antennas……proximity to tracks, proximity to fixed antennas…… Center: The designed configuration.11 existed antenna pads: red; 16 new antenna pads: blue.Center: The designed configuration.11 existed antenna pads: red; 16 new antenna pads: blue. Diameters of the circles are in scale with 25m.Diameters of the circles are in scale with 25m. Right: The tracks and connections are included.Right: The tracks and connections are included.


1.1. The designed VLA-E configuration has maximum side lobe ~12% for snapshot observation. VLA-D for The designed VLA-E configuration has maximum side lobe ~12% for snapshot observation. VLA-D for comparison has ~60%.comparison has ~60%.

2.2. The brightness temperature sensitivity is expected ~10 times better than VLA-DThe brightness temperature sensitivity is expected ~10 times better than VLA-D3.3. The cost of the array is minimized using the 11 existing antenna pads and the existing track at the north–The cost of the array is minimized using the 11 existing antenna pads and the existing track at the north–

east sector at the central part of VLA. Only one extra track (at the north-west sector) is added.east sector at the central part of VLA. Only one extra track (at the north-west sector) is added.4.4. Obviously the same 27 antennas are used Obviously the same 27 antennas are used

The two dimensional beam is at the left. The two orthogonal cross sections are at the rightThe two dimensional beam is at the left. The two orthogonal cross sections are at the right

The VLA-E configurationThe VLA-E configuration


LWA station configurationLWA station configuration

The primary beam of the LWA station element (dipole) is very wide (comparable with The primary beam of the LWA station element (dipole) is very wide (comparable with the whole hemisphere). So the optimization of the LWA station configuration should be the whole hemisphere). So the optimization of the LWA station configuration should be provided inside of the whole hemisphere. provided inside of the whole hemisphere. We carried out the optimization inside of the whole hemisphere for the shortest We carried out the optimization inside of the whole hemisphere for the shortest wavelength of the LWA’s operating frequencies and for zenith direction.wavelength of the LWA’s operating frequencies and for zenith direction.The circle of optimization for other (longer) wavelengths may be only larger. The circle of optimization for other (longer) wavelengths may be only larger.

Therefore if side lobes are optimized inside of the whole hemisphere for the Therefore if side lobes are optimized inside of the whole hemisphere for the shortest wavelength of the LWA’s operating frequencies they will be optimized for shortest wavelength of the LWA’s operating frequencies they will be optimized for any (longer) wavelength!any (longer) wavelength! Phasing the array to another (not zenith) direction, the whole beam pattern will be linearPhasing the array to another (not zenith) direction, the whole beam pattern will be linearshifted, if the sine of zenith angle is used for the coordinates instead of the shifted, if the sine of zenith angle is used for the coordinates instead of the zenith angle itself (see the following slide).zenith angle itself (see the following slide).

Therefore if we want to optimize the side lobe inside of the whole hemisphere for Therefore if we want to optimize the side lobe inside of the whole hemisphere for any phasing direction we need to optimize at zenith using the radius of optimization any phasing direction we need to optimize at zenith using the radius of optimization ! That is exactly what is done optimizing LWA station!!! ! That is exactly what is done optimizing LWA station!!!

)sin(z

2)sin( z



Beam pattern at 80MHz. Minimum spacing 2m. Beam pattern at 80MHz. Minimum spacing 2m. The optimization is done for The optimization is done for The maximum side lobe is 0.6% within the The maximum side lobe is 0.6% within the optimizing region.optimizing region. The left beam pattern is phased towards the The left beam pattern is phased towards the zenith. The right beam pattern is phased zenith. The right beam pattern is phased towards . The low right part towards . The low right part of the hemisphere is not covered by the of the hemisphere is not covered by the optimizing region. optimizing region. The optimization for is required!The optimization for is required!

450,600 azz

1)sin( z


The final LWA configuration design. The final LWA configuration design. Left: The configuration itself . The minimum spacing is as big as 5m Left: The configuration itself . The minimum spacing is as big as 5m to compromise with the mutual coupling between the dipoles. to compromise with the mutual coupling between the dipoles. The optimization is done for The optimization is done for Center: The two dimension beam pattern.Center: The two dimension beam pattern.Right: The two orthogonal cross sections of the beam pattern.Right: The two orthogonal cross sections of the beam pattern.

The side lobes of the designed LWA station configuration are never The side lobes of the designed LWA station configuration are never grater than 1.6% grater than 1.6% at any point in the sky regardless of at any point in the sky regardless of

phased direction or operating wavelength. phased direction or operating wavelength. The side lobes can be achieved much lower, if the minimum spacing The side lobes can be achieved much lower, if the minimum spacing

is chosen less. is chosen less. 2)sin( z

2)sin( z

January 13, 2011January 13, 2011 217th AAS Meeting-Seattle,WA217th AAS Meeting-Seattle,WA


ConclusionsConclusions

1.1.The side lobes of the designed LWA station configuration are never The side lobes of the designed LWA station configuration are never grater than 1.6% grater than 1.6% at any point in the sky regardless of phased at any point in the sky regardless of phased

direction or operating wavelengthdirection or operating wavelength. . 2.2.The minimum spacing is as big as 5m to compromise with the mutual The minimum spacing is as big as 5m to compromise with the mutual coupling between the dipoles. coupling between the dipoles. 3.3.The side lobes can be achieved much lower, if the minimum spacing is The side lobes can be achieved much lower, if the minimum spacing is chosen less. chosen less.





1.1.The designed VLA-E configuration has maximum side lobe ~12% for snapshot observation. VLA-D for comparison has ~60%.The designed VLA-E configuration has maximum side lobe ~12% for snapshot observation. VLA-D for comparison has ~60%.2.2.The brightness temperature sensitivity is expected ~10 times better than VLA-DThe brightness temperature sensitivity is expected ~10 times better than VLA-D3.3.The cost of the array is minimized using the 11 existing antenna pads and the existing track at the north–east sector at the central part of VLA. Only one extra track (at The cost of the array is minimized using the 11 existing antenna pads and the existing track at the north–east sector at the central part of VLA. Only one extra track (at the north-west sector) is added.the north-west sector) is added.4.4.Obviously the same 27 antennas are used Obviously the same 27 antennas are used




The beam pattern of the optimized E-configuration. The two dimensional The beam pattern of the optimized E-configuration. The two dimensional beam is at the left. The two orthogonal cross sections are at the rightbeam is at the left. The two orthogonal cross sections are at the right . .



UV coverage for different declinationsUV coverage for different declinations



The beam pattern of the optimized E-configuration. The two dimensional The beam pattern of the optimized E-configuration. The two dimensional beam is at the left. The two orthogonal cross sections are at the rightbeam is at the left. The two orthogonal cross sections are at the right . .



Sensitivity loss due to shadowing for different declinations and hour angles.Sensitivity loss due to shadowing for different declinations and hour angles.




1.1.The designed VLA-E configuration has maximum side lobe ~12% for snapshot observation. VLA-D for comparison has ~60%.The designed VLA-E configuration has maximum side lobe ~12% for snapshot observation. VLA-D for comparison has ~60%.2.2.The brightness temperature sensitivity is expected ~10 times better than VLA-DThe brightness temperature sensitivity is expected ~10 times better than VLA-D3.3.The cost of the array is minimized using the 11 existing antenna pads and the existing track at the north–east sector at the central part The cost of the array is minimized using the 11 existing antenna pads and the existing track at the north–east sector at the central part of VLA. Only one extra track (at the north-west sector) is added.of VLA. Only one extra track (at the north-west sector) is added.4.4.Obviously the same 27 antennas are used Obviously the same 27 antennas are used



L W AL W A



Beam pattern at 80MHz. Minimum spacing 2m. The optimization is done for Beam pattern at 80MHz. Minimum spacing 2m. The optimization is done for

The maximum side lobe is 0.6% within the optimizing region.The maximum side lobe is 0.6% within the optimizing region. The left beam pattern is phased towards the zenith. The right beam pattern isThe left beam pattern is phased towards the zenith. The right beam pattern is phased towards . The low right part of the hemisphere is not phased towards . The low right part of the hemisphere is not covered by the optimization area. covered by the optimization area. The optimization for can help!The optimization for can help!

1)sin( z

450,600 azz2)sin( z



Left: The designed 110mx100m LWA station configuration.Left: The designed 110mx100m LWA station configuration. The minimum spacing is increased to 5m to compromise with the The minimum spacing is increased to 5m to compromise with the mutual coupling between the dipoles. mutual coupling between the dipoles. The maximum side lobe is 1.6% within the optimizing regionThe maximum side lobe is 1.6% within the optimizing regionCenter: The two dimensional beam pattern. Center: The two dimensional beam pattern. Right: The two orthogonal cross sections of the two dimensional beam Right: The two orthogonal cross sections of the two dimensional beam pattern. pattern.

2)sin( z




1.1.The side lobes of the designed LWA station configuration are never The side lobes of the designed LWA station configuration are never grater than 1.6% grater than 1.6% at any point in the sky regardless of phased at any point in the sky regardless of phased

direction or operating wavelengthdirection or operating wavelength. . 2.2.The minimum spacing is as big as 5m to compromise with the mutual The minimum spacing is as big as 5m to compromise with the mutual coupling between the dipoles. coupling between the dipoles. 3.3.The side lobes can be achieved much lower, if the minimum spacing is The side lobes can be achieved much lower, if the minimum spacing is chosen less. chosen less.



AbstractAbstract

An optimization algorithm designed by Leonid Kogan (An optimization algorithm designed by Leonid Kogan (L. Kogan “Optimizing a Large L. Kogan “Optimizing a Large Array Configuration to Minimize Side Lobes”,Array Configuration to Minimize Side Lobes”, IEEE Transactions on Antennas and IEEE Transactions on Antennas and Propagation, vol 48, No 7, July 2000, p 1075) to minimize side lobes in the point Propagation, vol 48, No 7, July 2000, p 1075) to minimize side lobes in the point spread function has been applied in the design of two new radio-interferometric arrays: spread function has been applied in the design of two new radio-interferometric arrays: (1) the most compact (E) configuration of EVLA and (2) the phased-array station for (1) the most compact (E) configuration of EVLA and (2) the phased-array station for the Long Wavelength Array (LWA). Scientific programs for the EVLA’s E-configuration the Long Wavelength Array (LWA). Scientific programs for the EVLA’s E-configuration includes galactic and local HII, molecular gas, cosmic web, radio continuum, radio includes galactic and local HII, molecular gas, cosmic web, radio continuum, radio lobes, SZ effect, cosmology and pulsar searches. The LWA will operate at frequencies lobes, SZ effect, cosmology and pulsar searches. The LWA will operate at frequencies 10-88 MHz and will study a wide range of scientific programs including clusters of 10-88 MHz and will study a wide range of scientific programs including clusters of galaxies, high-redshift radio galaxies, pulsars, SNR’s, extra solar planets, solar and galaxies, high-redshift radio galaxies, pulsars, SNR’s, extra solar planets, solar and ionospheric physics. Both arrays need to be compact and to have the smallest side ionospheric physics. Both arrays need to be compact and to have the smallest side lobes possible. The EVLA’s E-configuration was designed minimizing the cost by lobes possible. The EVLA’s E-configuration was designed minimizing the cost by requiring only one new track and using the 11 existed antenna pads. The achieved requiring only one new track and using the 11 existed antenna pads. The achieved side lobe level for snapshot observation is ~12% within the antenna primary beam for side lobe level for snapshot observation is ~12% within the antenna primary beam for any operating VLA wavelength. any operating VLA wavelength. For comparison the VLA-D configuration has For comparison the VLA-D configuration has sidelobes ~60%.sidelobes ~60%. For the LWA station configuration the side lobes For the LWA station configuration the side lobes are never grater are never grater than 1.6% than 1.6% at any point in the sky regardless of phased direction or operating at any point in the sky regardless of phased direction or operating wavelength. wavelength. Such a small side lobes for both arrays promise very high image fidelity Such a small side lobes for both arrays promise very high image fidelity for maximum scientific results.for maximum scientific results.



Why do we need the most compact E-configuration?Why do we need the most compact E-configuration?To get better Surface Brightness Sensitivity.To get better Surface Brightness Sensitivity.

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Configuration figures of merit.Configuration figures of merit.

• Minimum side lobesMinimum side lobes• Gaussian shape of the main beamGaussian shape of the main beam• Minimum gaps in the UV coverageMinimum gaps in the UV coverage• OthersOthers

Optimizing figures of merit other than “Minimum side lobes” improves the Optimizing figures of merit other than “Minimum side lobes” improves the side lobes implicitly, but the direct minimum side lobe optimization may side lobes implicitly, but the direct minimum side lobe optimization may produce better result. produce better result.

We optimize the array configuration minimizing the maximum We optimize the array configuration minimizing the maximum positive side lobe inside of the primary beam!positive side lobe inside of the primary beam!

Kogan 2000, IEEE Transaction on Antennas and Propagation, 48, 7, Kogan 2000, IEEE Transaction on Antennas and Propagation, 48, 7, 10751075



The final configuration. The minimum spacing is increased to 5m to The final configuration. The minimum spacing is increased to 5m to compromise with the mutual coupling between the dipoles. The compromise with the mutual coupling between the dipoles. The optimization is done for optimization is done for 2)sin( z



Mathematically created mask to prevent appearance of antennas Mathematically created mask to prevent appearance of antennas (during optimization) on the prohibited places: proximity to tracks, (during optimization) on the prohibited places: proximity to tracks, proximity to fixed antennas……proximity to fixed antennas……



One dimensional beam (along RA) of the optimized E-configurationOne dimensional beam (along RA) of the optimized E-configuration



One dimensional beam (along DEC) of the optimized E-configurationOne dimensional beam (along DEC) of the optimized E-configuration



217th AAS Meeting-Seattle,WA217th AAS Meeting-Seattle,WAJanuary 13, 2011January 13, 2011


Beam pattern at 80MHz phased towards Beam pattern at 80MHz phased towards Minimum spacing 2m. Minimum spacing 2m.

450,600 azz



L. Kogan , F. Owen , J. Ott , A. Cohen National Radio Astronomy Observatory Socorro, NM USA

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