An augmented coprime array systematically employs two sparse subarrays to produce a large-scale difference co-array with attractive merits, such as enhanced degrees of freedom (DOFs) and enlarged array aperture, whereas the interleaved subarrays are susceptible to mutual coupling. In this paper, we propose an unfolded augmented coprime array (UACA) obtained by careful crafting of small sparse subarrays to fill the holes in the difference co-array generated by unfolding operation. Specifically,

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... ACA can significantly reduce the number of sensor pairs with small spacing and hence inherently weaken the mutual coupling effect. Meanwhile, an increase of the DOFs and improved direction of arrival (DOA) estimation accuracy can be achieved in the presence of mutual coupling. As an application of UACA, we propose a decoupled interference-plus-noise covariance matrix (INCM) reconstruction method for robust adaptive beamforming (RAB) with UACA. Therein, mutual coupling coefficients are estimated based on the remodeled contaminated steering vector and the noise subspace. The estimated mutual coupling matrix is utilized to reconstruct the decoupled covariance matrix which in turn is used to obtain refined DOA estimates, interferer power estimates, and the desired INCM. Extensive simulation results are provided to verify the effectiveness of UACA and the decoupled INCM reconstruction method for RAB. INDEX TERMS Coprime array, mutual coupling, DOA estimation, robust adaptive beamforming. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see http://creativecommons.org/licenses/by/4.0/ VOLUME 8, 2020