march, 2009 spdo meeting design of arrays minimizing side lobes leonid kogan national radio...
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March, 2009 SPDO meeting
Design of Arrays minimizing Side Lobes
Leonid Kogan
National Radio Astronomy Observatory
March, 2009 SPDO meeting
Configuration figures-of-merit.
• Minimal side lobes• Gaussian shape of the main beam• Minimal gaps in the UV coverage• OthersOptimizing 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.
March, 2009 SPDO meeting
Which side lobes to optimize:Positive or Negative?
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Function SpreadPoint is PSF
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March, 2009 SPDO meeting
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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?
March, 2009 SPDO meeting
Where to move antennas?
March, 2009 SPDO meeting
How much should an array antenna move along the found direction?
),( exBP 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
exxx n
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March, 2009 SPDO meeting
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.
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
March, 2009 SPDO meeting
An ALMA Largest Configuration Optimized with Matching the Terrain at the Chajnantor Site(Chile)
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
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 0.0056 (22.5dB)
March, 2009 SPDO meeting
Slice of the above beam pattern along DEC
March, 2009 SPDO meeting
Slice of the above beam pattern along RA
March, 2009 SPDO meeting
LWA antenna station with 256 dipoles.The beam pattern is phased toward zenith angle 60, azimuth
45.
March, 2009 SPDO meeting
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%.
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%
March, 2009 SPDO meeting
DSN array120 of 12 meter dishes
Side lobes ~25db