Abstract
A minimum gradient algorithm for phased-array null formation
National Radio Astronomy Observatory, Socorro, New Mexico, USA
Formation of the null at the phased-array beam pattern pointed toward the source of a radio frequency interference (RFI) can
serve to mitigate the effects of that RFI. Several algorithms for creating a null at the phased-array beam pattern have been
designed. On the basis of an array side lobe minimization algorithm (Kogan, 2000), a new method for creating a null at the
phased-array beam pattern is described here. The algorithm is a straightforward one and can have an advantage in creating
wide-area nulls, especially for phased arrays with a small number of antennas. We have tested this algorithm for a possible
Square Kilometre Array antenna station configured as a phased array of 19 antennas and for the Very Large Array configuration
D (VLA-D), working as a phased array for very long baseline interferometry experiments. The null is created at the given area
around the given direction. The narrow null (∼0.1
) deeper than 100 dB level can be achieved at the cost of a 2% decrease in the signal-to-noise ratio in the main direction.
The creation of such a deep null can be impractical for many reasons, however, first and foremost because the phases and weights
would have to be specified with impractical precision. Rounding the phase and weights to 1° and 0.01, respectively raises
the null up to ∼50 dB.
Received 2 August 2004; accepted 1 March 2005; published 30 April 2005.
Citation: (2005), A minimum gradient algorithm for phased-array null formation, Radio Sci., 40, RS2S90, doi:10.1029/2004RS003140.
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