Bandwidth selective filter for the pre-excision of narrowband interference in broadband beamformers

A novel frequency domain excision filter for use in front of broadband adaptive beamformer systems is presented. The proposed frequency domain excision filter uses image processing techniques to determine the excision threshold such that only narrowband interference is removed from the received signal. By pre-excising the received signal of narrowband interference the adaptive beamformer only has to remove partialband or broadband interferers. This frees up degrees of freedom (DoF) in the adaptive beamformer in mixed interference environments allowing for a greater interference suppression capability. The proposed pre-excision system is simulated using a constrained space-time adaptive processor as well as a constrained sub-optimal space-frequency adaptive processor. It is shown that when pre-excision is used in front of a beamformer the total number of interference sources that can be simultaneously rejected is increased as long as the beamformer´s DoF are exceeded by narrowband interference.