Phase-Optimised Linearly-Constrained Minimum-Variance Beamformers

Abstract A procedure for the determination of the optimal group-delay of a Linearly-Constrained Minimum-Variance (LCMV) beamformer is described. The beamformer’s complex response in the look direction and at the carrier frequency is specified using derivatives. A broad null may also be placed at the Nyquist frequency to attenuate high-frequency noise. Given a spatiotemporal noise–covariance matrix, that describes the interference environment, the proposed constraints allow the noise power to be expressed as a polynomial in the beamformer’s group delay. The optimal delay that minimizes the power is then set as the phase centre of the array and used to evaluate the beamformer’s coefficients. The delay is used as an extra degree of freedom to refine the response of a low-order LCMV beamformer.