Effect of element errors on half-power beamwidth of the Capon adaptive beamformer

The Capon beamformer can perform accurate bearing estimation by taking advantage of the fact that for high input signal-to-noise ratios, the "adaptive beamwidth" is much narrower than the classical Rayleigh limit. This paper studies the effect of random antenna element errors on this adaptive beamwidth. The imperfections considered are amplitude and phase errors which are constant during the period of adaptation. With a single input point-source signal, it is shown that the Capon beamformer half-power beamwidth is degraded by array aberrations, but it is still several times better than that of conventional nonadaptive delay-and-sum beamformers, provided the input signal-to-noise ratio is 0 dB or higher. A simple scalar formula is derived to predict the Capon half-power beamwidth in the presence of element errors for uniformly spaced line arrays, and computer simulation data are presented to verify its accuracy to within 4 percent.