Narrowband line-array beamforming: practically achievable resolution limit of unbiased estimators

Based on an approximation to the Cramer-Rao lower bound, it is demonstrated that meaningful resolution with an unbiased narrowband estimator requires a source separation of at least about 1/10 of a Rayleigh beamwidth, even under ideal circumstances, with 1/4 beamwidth being a more practically achievable figure.<
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