Supplementary coprime array with enhanced DOFs exploiting hole filling strategy based on the difference and sum coarray

Recently, coprime array has attracted much attention for DOA estimation since it can provide high degrees of freedom (DOFs) by exploiting the difference and sum coarray (difference-sum coarray). However, the achievable number of uniform DOFs of coprime array is limited by the holes in the difference-sum coarray. In this paper, we propose a new coprime configuration named supplementary coprime array (SCA) to tackle the problem through the following three steps. We first analyze the structure of the difference-sum coarray and provide the closed-form expression of the hole positions. Then, we remove some unimportant sensors from the conventional coprime array to reduce the coarray redundancy, which brings a few new holes in the difference-sum coarray. Finally, we construct a supplementary subarray to fill the holes using the removed unimportant sensors. As a result, the proposed SCA can significantly increase the number of DOFs without introducing new sensors, and reduce the mutual coupling effect at the same time. Numerical simulations are provided to verify the effectiveness of the proposed array configuration.