Extended sum and difference coarray design via motion strategies: Enhanced DOA estimation for non-circular signals with CADiS arrays

Recently, the use of moving arrays for direction of arrival (DOA) estimation has garnered significant attention. Nevertheless, research on the application of moving arrays for DOA estimation of non-circular (NC) signals remains scarce. Coprime array with displaced subarray (CADiS) has gained considerable attention due to its large aperture and low mutual coupling characteristics. In this paper, we first investigate the expression for the sum coarray (SCA) generated by array motion. Based on the hole distribution in the CADiS configuration, we then propose a hole-free motion strategy. This method effectively fills all holes in the difference coarray (DCA) and SCA, resulting in a hole-free sum and difference coarray (SDCA). Furthermore, we propose a simplified array motion strategy to achieve hole-free SDCA with only single-step motion, and provide the closed-form expression for the maximum achievable uniform degrees of freedom (uDOFs). Finally, we demonstrate the superiority of the proposed methods in comparison to other arrays in terms of uDOFs, DOA estimation performance of NC signals, angular resolution, and the number of identifiable sources.