Fragmented coprime arrays with optimal inter subarray spacing for DOA estimation: Increased DOF and reduced mutual coupling

Sparse arrays possess attractive features compared to uniform linear arrays (ULAs) with increased degrees of freedom (DOFs), reduced mutual coupling, and enlarged array aperture, which improves the estimation performance of arrays. Recently, coprime arrays have attracted increasing attention due to reduced mutual coupling, whereas the holes in the difference coarray degrade the uniform coarray. In this paper, we propose a new array configuration called the fragmented coprime array with optimal inter-subarray spacing (FCAOIS). FCAOIS configuration maximizes the intra-subarray spacing of a fragmented coprime array (FCA) and incorporates two interlayer subarrays into the FCA, where the holes in the difference coarray of FCA are the results of the two missing interlayer subarrays. An extended array geometry from FCAOIS is also presented to lengthen the uniform difference coarray. It is noteworthy that the proposed coprime arrays outperform nested arrays in mitigating mutual coupling and especially in the scale of uniform difference coarray. Simulation results validate the superiorities of the proposed FCAOISs over other sparse arrays.