Multi-Rank Adaptive Beamforming

This paper presents a multi-rank generalization of the Capon beamformer to accommodate model mismatch in situations where the unknown signal of interest lies in a multidimensional subspace. By expanding the beamforming subspace robustness (or diversity) is achieved at the expense of resolution. The generalization involves solving a quadratically-constrained quadratic minimization problem, and designing a constraint matrix. Three strategies for designing this constraint matrix are discussed. Simulation examples are presented to demonstrate the performance of the multi-rank Capon beamformer