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


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


Which side lobes to optimize:Positive or Negative?

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• 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?


Where to move antennas?


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:

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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.


An ALMA Largest Configuration Optimized with Matching the Terrain at the Chajnantor Site(Chile)


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


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%.


SKA antenna station.The antenna diameter 12 meter.

The side lobes are optimized inside of the primary beam.

Maximum side lobe ~3%


DSN array120 of 12 meter dishes

Side lobes ~25db


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)


Slice of the above beam pattern along DEC


Slice of the above beam pattern along RA


LWA antenna station with 256 dipoles.The beam pattern is phased toward zenith angle 60, azimuth

45.

june, 2006 asc presentation design of arrays with minimum side lobes leonid kogan national radio...

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