Abstract
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, UACA 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.
Highlights
The small spacing between the adjacent antenna elements in traditional dense arrays is typically limited to half wavelength or less to avoid spatial aliasing, which leads to significant mutual coupling and restricted array aperture
unfolded augmented coprime array (UACA) can significantly decrease the number of sensor pairs with small spacing, i.e. d, 2d, · · ·, and inherently weaken the mutual coupling effect in the case d = λ/2
We first unfold the interleaved subarrays in augmented coprime array (ACA) to enlarge the array aperture and decrease the number of sensor pairs with small spacing, which are the main cause of the mutual coupling
Summary
The small spacing between the adjacent antenna elements in traditional dense arrays is typically limited to half wavelength or less to avoid spatial aliasing, which leads to significant mutual coupling and restricted array aperture. In [36], the mutual coupling coefficients were estimated by a subspace-based method, VOLUME 8, 2020 allowing the calculation of a refined (compensated) beamforming weight vector. We firstly 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 the unfolding operation. We first unfold the interleaved subarrays in ACA to enlarge the array aperture and decrease the number of sensor pairs with small spacing, which are the main cause of the mutual coupling. IT ∈ RT ×T denotes the identity matrix with ones at the principal diagonal
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