Adaptive broadband beamforming: an integral nulling approach

A combination of an integral and null constraints is used to produce broad nulls. The broad null is realized by using a broad null constraint to cover an angular region or a frequency band instead of a set of narrow null constraints or derivative null constraints. A specified region in the spatial or frequency domains is null-constrained by combining the integral of the gain function with respect to the region with the null constraint, while maintaining unit gain in the desired direction and frequency. It is assumed that the spatial region or frequency band of the jammer is known. It is shown that the nulling capability is improved by using integral null constraints in the spatial as well as the frequency domains. One integral null constraint was implemented in the Frost beamformer (O.L. Frost, III, Proc. IEEE, vol.60, no.8, p.926-35, Aug. 1972) with directional constraints for the spatial and frequency domains; simulation results are reported