June, 2006 ASC presentation Design of Arrays with Minimum Side Lobes Leonid Kogan National Radio...
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Transcript of June, 2006 ASC presentation Design of Arrays with Minimum Side Lobes Leonid Kogan National Radio...
June, 2006 ASC presentation
Design of Arrays with Minimum Side Lobes
Leonid KoganNational Radio Astronomy
Observatory
June, 2006 ASC presentation
List of some arrays planned in soon future.
• ALMA Atacama Large Millimeter Array. 64 of 12 meter dishes Chile. Altitude >5000m• SKA Square Kilometer Array• EVLA Expanded VLA Most compact E-configuration NMA (New Mexico Array)• DSN 100 of 12 meter dishes• ATA Allen Telescope array of SETI 350 of 6.1 meter dishes• LWA Long Wavelength Array• ~40 antenna stations of 256 dipoles each
June, 2006 ASC presentation
Which side lobes to optimize:Positive or Negative?
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June, 2006 ASC presentation
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June, 2006 ASC presentation
• Q1. Where should each array antenna move to decrease the value of the array beam pattern (Point Spread function - PSF)?
• Q2. How much should each of the array antennas move along the found direction to decrease the value of the array beam pattern (Point Spread Function - PSF) at the given direction?
June, 2006 ASC presentation
Where to move antennas?
June, 2006 ASC presentation
How much should an array antenna move along the found direction?
),( exP n nx
nThe derivative of the function by
determines how far is the antenna from the optimum
Therefore the required shift of the given antennaIs proportional to the relevant derivative:
))(2sin(1
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June, 2006 ASC presentation
The AIPS task CONFICONFI can design an optimum configuration using multi iteration process.
The direction toward the biggest side lobe is found on each iteration. The algorithm described above is used at each iteration.
Each antenna is moved by a small portion of the calculated value determined by the input parameter gain which gain which should be small (<<1) .should be small (<<1) .
The topography constrain, minimum spacing, bound of the configuration, several initial configurations and many other features are available.
June, 2006 ASC presentation
An ALMA Largest Configuration Optimized with Matching the Terrain at the Chajnantor Site(Chile)
June, 2006 ASC presentation
Alma compact configuration optimized having topography file of the roads.
The side lobes optimized inside of a part of the primary beam.Maximum side lobe ~0.009
June, 2006 ASC presentation
EVLA compact configuration.The size of the dots (red are existing pads) shows the antennadiameter 25 meter. The side lobes are optimized inside of the
primary beam. Maximum side lobe ~5%.
June, 2006 ASC presentation
SKA antenna station.The antenna diameter 12 meter.
The side lobes are optimized inside of the primary beam.
Maximum side lobe ~3%
June, 2006 ASC presentation
DSN array120 of 12 meter dishes
Side lobes ~25db
June, 2006 ASC presentation
LWA antenna station with 256 dipoles.Minimum spacing 2m.
The area of optimization is the whole semi-sphere.The side lobes are less than 0.0056 (22.5dB)
June, 2006 ASC presentation
Slice of the above beam pattern along DEC
June, 2006 ASC presentation
Slice of the above beam pattern along RA
June, 2006 ASC presentation
LWA antenna station with 256 dipoles.The beam pattern is phased toward zenith angle 60, azimuth
45.