Adaptive broadband frequency invariant beamforming using nulling-broadening and frequency constraints

The performance of conventional adaptive broadband beamforming algorithms is degraded because of rapidly moving interferences and look-direction errors. In this paper, a number of techniques are proposed to overcome this issue. By proposing an adaptive frequency invariant beamformer (FIB) that uses frequency constraints, we can obtain undistorted responses to broadband signal of interests (SOIs) and constant beamwidths over an entire frequency band without pre-steering delays. And the influence of look-direction errors can also be receded. Furthermore, a singular value decomposition of the frequency constraints is added to the proposed algorithm in view of releasing numerous degrees of freedom (DOFs), as this approach can simultaneously maintain the enhanced anti-interference performance and hold the undistorted response to SOIs. Finally, the nulling-broadening method involving the use of virtual interferences is adopted to construct a taper matrix and ensure robust performance versus rapidly moving interferences. This robust response to rapidly moving interferences and look-direction errors allows the proposed algorithm to achieve satisfactory broadband beamforming performance. Simulation results highlight the correctness and effectiveness of the proposed methods.