I. Introduction
The estimation problem of the direction of arrival (DOA) has been studied for decades in different applications encompassing radar, wireless communications, and array signal processing [1]. Traditionally, the DOA is estimated by the discrete Fourier transform (DFT)-based methods [2]–[4], where the antenna arrays provide spatial samplings. The DFT-based methods realize the DOA estimation via the DFT of received signals spatially sampled by the antenna array, with its inherent sampling resolution characterized by the Rayleigh criterion [5].