System noise reduction through null steering in large wideband sparse arrays

Null steering is an important beam-forming technique for phased antenna arrays in general particularly in applications involving high interference. In radio astronomy, where the signal of interest may be much weaker than interference (particularly from manmade sources) a severe limitation may occur on the system noise temperature, dynamic range and processing budget at interfering frequencies. One way of minimizing this impact is via null steering. For large wideband sparse array system such as the SKA-AALO, traditional null steering techniques are inappropriate due to the sparse geometry. Some methods have been reported using numerical techniques, but due to the large number of antenna elements involved and the random element distribution these require long computations and search methods to obtain pattern control. In this paper, a deterministic and computationally simple null steering technique is introduced which can be directly applied to null multiple interference sources. The weights for several nulls can be directly computed from the array radiation pattern data regardless of element distribution making it particularly useful for sparse arrays operating over a large bandwidth.