How to enhance the desired signal with low signal-to-noise ratio (SNR) is a difficult problem in the estimation process of the direction-of-arrival (DOA) of the target scattering wave signal. In this paper, the feasibility of spatial spectrum estimation in the Range-Doppler (RD) domain is analyzed in principle, and the SNR gain expression of weak scattering wave signal is derived when constructing multi-snapshots virtual array data. On this basis, the mutual eigenvector singular value decomposition (MESVD) method based on RD domain mode excitation is proposed, which can robustly and effectively estimate the direction of the coherent weak signals. Simulation experiments verify that the RD domain spectral estimation method has the ability to simultaneously obtain the direction of multiple weak target scattering waves, and the direction-finding accuracy can reach the Cramer–Rao bound (CRB) of conventional spectral estimation method. The results of Monte Carlo experiments show that the root-mean-square-error (RMSE) of azimuth estimation of RD domain spatial spectrum estimation method is 5.76° lower than that of a conventional multiple signal classification (MUSIC) method. In addition, the practicability of the proposed method is demonstrated by comparing the DOA estimation results of a set of real data with Automatic Dependent Surveillance-Broadcast (ADS-B) data.

In the directional antenna element-based uniform arc array (DA-UAA), the conventional spatial spectrum estimation algorithms such as multiple signal classification could not be utilized to find the direction-of-arrival (DOA) of an incident electromagnetic wave because of the incomplete information about the radiation pattern and polarization characteristics of each array element. In this article, a collection of DOA estimation algorithms for cases with incomplete DA-UAA manifold information is proposed. First, the received signal model of the DA-UAA is analyzed, and an active calibration method for array receivers, incorporating de-embedding equalization filtering to address the interchannel amplitude and phase inconsistencies, is proposed. Based on the traditional omni-directional amplitude-comparison DOA estimation method, the cosine-series expansion-based multiantenna amplitude-comparison DOA estimation method is adopted by the DA-UAA. Second, the low-order Legendre polynomial-based difference-sum amplitude-comparison DOA estimation algorithm and the Legendre-series-based root-seeking amplitude-comparison DOA estimation method are proposed to combine computational complexity and direction-finding accuracy. Third, an eigen subspace projection-based successive suppression amplitude-comparison DOA estimation strategy is designed to handle multiple incident waves with the same frequency. Finally, the effectiveness and accuracy of these proposed algorithms are verified through numerical simulations and field experiments, with the Cramér-Rao Lower Bound analyzed simultaneously.