Improved Coprime Arrays With Reduced Mutual Coupling Based on the Concept of Difference and Sum Coarray

As is well known, the prototype coprime arrays consist of two collinear subarrays, whose physical sensor number is coprime to each other. Moreover, their larger inter-element separations and physical array apertures make them have less mutual coupling than uniform linear arrays. Even so, there is still mutual coupling existing in them, which has an adverse effect on the direction of arrival estimation. To reduce the effects of mutual coupling, several improved coprime configurations based on the concept of difference and sum coarray are proposed in this paper, which can be obtained through three operations. The first one is to shift the prototype coprime array to obtain the translational coprime arrays, which can help to reduce the redundancy between the difference coarray and sum coarray. Second, flip one of the subarrays in the translational coprime arrays with zero points as the symmetric center to get the flipped coprime arrays, which can expand the physical array aperture and inter-element separations further. Finally, move one of the symmetrically placed sensors in the flipped coprime arrays to zero points. Then, the proposed arrays are derived. They have almost the same consecutive degrees of freedom (DOFs) as the prototype coprime array but dramatically reduced mutual coupling due to their larger physical array apertures and inter-element separations, where the virtual arrays are constructed by their respective difference and sum coarray. In the end, the numerical simulation results confirm the superiority of proposed arrays.