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The adaptive antenna array beamforming is used to suppress jammers by placing antenna directional pattern nulls in the directions of the jammer sources. The performance of the beamformer is known to degrade in rapidly moving jammer environments. This degradation occurs due to the jammer motion that can bring the jammers out of the sharp nulls of the adaptive directional pattern. The directional pattern nulls broadening is an effective means to settle this problem. To broaden the nulls, the first derivative of the pattern in the directions of the jammer sources is set equal to zero. Being applied to the beamformer with a linear array, this technique allows producing broaden  nulls in the directional pattern. However, in the case of a two-dimensional planar antenna array, the nulls will broaden only in one angular plane. In order to equally broaden the nulls in all angular directions and in this way to make them symmetrical, some additional constraints on the second partial derivatives of the directional pattern should be imposed. To set these constraints, it is necessary to include additional transformed steering vectors of jammers in the basis of the jammer subspace. These new transformed steering vectors are calculated in accordance with the expressions for the second partial derivatives of the directional pattern. In this paper, the expressions for the transformed steering vectors are derived and a novel beamforming algorithm based on them is proposed. In the adaptive beamforming algorithm based on such an approach unknown steering vectors of jammers are replaced by the eigenvectors of the sample covariance matrix corresponding to the largest eigenvalues. The effectiveness of the proposed method is verified by the computer simulation results. The computational complexity of this algorithm is estimated.

Forming broaden dips in the directional pattern of an adaptive spatial filter with planar antenna array.