Sparse Extension Array Geometry for DOA Estimation With Nested MIMO Radar

The two-level nested array geometry, which systematically nests two uniform linear subarrays, is proved to offer O(N2) degrees of freedom (DOFs) with only N sensors. In this paper, a novel sparse extension array geometry for nested multiple-input multiple-output radar is proposed to provide O(N4) DOFs with N sensors. In the proposed geometry, both the transmitter and receiver are equipped with the two-level nested arrays, where we particularly extend the inter-element spacing of the transmitter with a sparse extension factor, leading to a great increase of DOF. Furthermore, we derive the closed-form expressions for the sensor locations and the available DOFs. Spatial smoothing-based MUSIC algorithm is employed to validate the effectiveness and superiority of the proposed sparse extension array for direction of arrival estimation.