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March, 2009 SPDO meeting Design of Arrays minimizing Side Lobes Leonid Kogan National Radio Astronomy Observatory.

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Presentation on theme: "March, 2009 SPDO meeting Design of Arrays minimizing Side Lobes Leonid Kogan National Radio Astronomy Observatory."— Presentation transcript:

1 March, 2009 SPDO meeting Design of Arrays minimizing Side Lobes Leonid Kogan National Radio Astronomy Observatory

2 March, 2009 SPDO meeting OUTLINE Comparison of configuration figures-of-merit Which side lobes to optimize, positive or negative? Connection of the Point Spread Function to the Beam pattern. Brief description of the algorithm. AIPS tasks CONFI and UVCON Examples of projects where arrays were designed using this side lobe minimizing algorithm

3 March, 2009 SPDO meeting Configuration figures-of-merit. Minimal side lobes Gaussian shape of the main beam Minimal gaps in the UV coverage Others Optimizing figures of merit other than “Minimal side lobes” improves the side lobes level implicitly, but a direct minimal side lobes optimization may produce better results.

4 March, 2009 SPDO meeting Which side lobes to optimize: Positive or Negative?

5 March, 2009 SPDO meeting

6 March, 2009 SPDO meeting Q1. In which direction should each array antenna be moved to decrease the value of the array Beam Pattern (Point Spread function - PSF)? Q2. How far should each array antenna be moved to decrease the value of the array Beam Pattern (Point Spread Function - PSF) in that direction?

7 March, 2009 SPDO meeting Where to move antennas?

8 March, 2009 SPDO meeting How much should an array antenna move along the found direction? The derivative of the function by determines how far is the antennafrom the optimum Therefore the required shift of the given antenna Is proportional to the relevant derivative:

9 March, 2009 SPDO meeting The AIPS task CONFI CONFI can design an optimum configuration using an iterative method. During each iteration the direction of the biggest side lobe is computed. Then the algorithm of the described above is applied. Each antenna is moved by a small portion of the calculated value determined by a small (<<1) input parameter gain. Various parameters can be constrained, such as topography, minimum spacing, configuration bounds, several initial configurations.

10 March, 2009 SPDO meeting List of some arrays optimized minimizing side lobes. ALMA Atacama Large Millimeter Array. SKA Square Kilometer Array (Antenna station) EVLA. Most compact E-configuration DSN 100 of 12 meter dishes LWA: Long Wavelength Array. Antenna station of 256 dipoles each

11 March, 2009 SPDO meeting An ALMA Largest Configuration Optimized with Matching the Terrain at the Chajnantor Site(Chile)

12 March, 2009 SPDO meeting 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

13 March, 2009 SPDO meeting LWA antenna station with 256 dipoles. Minimum spacing 2m. The area of optimization is the whole semi-sphere. The side lobes are less than (22.5dB)

14 March, 2009 SPDO meeting Slice of the above beam pattern along DEC

15 March, 2009 SPDO meeting Slice of the above beam pattern along RA

16 March, 2009 SPDO meeting LWA antenna station with 256 dipoles. The beam pattern is phased toward zenith angle 60, azimuth 45.

17 March, 2009 SPDO meeting EVLA compact configuration. The size of the dots (red are existing pads) shows the antenna diameter 25 meter. The side lobes are optimized inside of the primary beam. Maximum side lobe ~5%.

18 March, 2009 SPDO meeting SKA antenna station example. The antenna diameter 12 meter. The side lobes are optimized inside of the primary beam. Maximum side lobe ~3%

19 March, 2009 SPDO meeting DSN array 120 of 12 meter dishes Side lobes ~25db


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