In this paper, we investigate the issue of direction of arrival (DOA) estimation of non-circular (NC) signals, and propose a modified nested array with enhanced degrees of freedom (DOFs) and a vectorized NC propagator method (VNC-PM) algorithm which can utilize the difference-sum co-array to perform DOA estimation. Specifically, we modify the conventional nested array by switching the positions of the two subarrays aiming to obtain a difference-sum co-array with higher DOFs. In order to fully exploit the provided DOFs and obtain higher estimation accuracy, we utilize the NC characteristic to generate the equivalent received signal of the difference-sum co-array and exploit the quasi-stationary property of the signal to avoid the spatial smoothing technique which leads to the DOF degradation. The modified PM based on the rotational invariance is then employed to obtain DOA estimates, where NC phases can be eliminated. Simulations are provided to evaluate the superiority of the proposed configuration and DOA estimation algorithm.

DOA estimation; non-circular signals; nested array; difference-sum co-array