Flexible robust adaptive beamforming method with multiple separately widened nulls

With the development of the array signal processing techniques, more and more robust methods are proposed for non‐stationary interference cancellation at the beamforming stage. Among these methods, null widening methods or well‐known covariance matrix taper (CMT) methods are the research hotspots. However, the typical CMT‐class methods modified the whole covariance matrix with the same taper matrix, which means that all the nulls produced by the covariance matrix will be widened to the same width in cosine angular domain. This will make a waste of degrees of freedom (DOFs) in the scene that different interference sources have a different degree of non‐stationarity. In this Letter, also adopting CMT structure, a flexible widening method is discussed, which utilises the relationship between each eigenvector and the steering vector of each interference source. The proposed method can widen different nulls with different width, which can save the consumption of DOFs as many as possible according to the demand. Besides, as a subspace‐based method, it can preserve the minimal sample support property. The simulation results show the effectiveness of the proposed method.