An Efficient DoA Estimation Approach for 2-D Planar Array Antennas via Axial Decomposition of Antenna Current Green's Function

Array manifold, constructed from the received signals by incoming waves in antenna arrays, serves as a fundamental framework for characterizing electromagnetic behavior in direction finding systems. For densely arrayed 2-D planar antenna systems, strong inter-element mutual coupling distorts the array manifold, which directly degrading direction finding performance. While electromagnetic numerical techniques can be used to analyze mutual coupling effects in receiving antenna systems, large computational costs are required for 2-D array structures. This paper presents a fast reciprocal analysis method, based on a directional decomposition approach, for mutual coupling characterization of 2-D receiving antenna systems. The proposed method incorporates antenna current Green's function theory to analyze the reciprocal property between transmit and receive modes of 2-D array antennas. Through directional decomposition, 2-D array problem is transformed into two separate 1-D array analyses, reducing computational complexity from O(M-B(2)((NxNy3)-N-3)) to O(M-B(2)(N-x(3)+N-y(3))) . Building upon previous work that effectively characterized transmit-mode behavior, this study validates the directional decomposition approach in receiving modes based on reciprocity. The approach accurately predicts both receive-mode antenna current Green's function and array manifolds while preserving mutual coupling and truncation effects. Validation is performed through direction finding scenarios. Validation through comparison with full-wave analysis demonstrates high correlation in array manifold components across all observation angles ( theta:-63 degrees to 63 degrees, phi:-126 degrees to 126 degrees). In direction of arrival estimation applications with various multiple-source scenarios, the method achieves angular resolution comparable to conventional full-wave analysis while reducing computation time to 0.18% of the original requirement.