Coprime Transformed Nested Array with Enhanced DOFs and Reduced Mutual Coupling Based on the Difference and Sum Coarray

Recently, the concept of the difference and sum coarray has attracted increasing interest in the direction of the arrival estimation field because it can generate enhanced degrees of freedom. In this paper, we propose an improved transformed nested array design strategy by relaxing the constraints on the dense subarray of the transformed nested array. Then, three conditions are given for the array design to ensure the continuity of the difference and sum coarray. Based on the strategy, we develop a novel nested configuration named coprime transformed nested array (CTNA) whose dense subarray is a coprime structure, and the closed-form expressions for the sensor positions and the range of consecutive coarray are derived. CTNA can increase the number of degrees of freedom (DOFs) compared to the existing nested arrays, while the mutual coupling effect can be maintained at the same low level as the coprime arrays, which indicates that CTNA has the merits of both nested array and coprime array. Numerical simulations are performed to verify the superiority of the proposed array configuration in terms of the number of DOFs, mutual coupling and direction of arrival (DOA) estimation accuracy.