Resolving target and image in low altitude scenarios in synthetic impulse and aperture radars

Low-angle direction of arrival (DOA) estimation is a challenging issue in array processing systems. When the target’s elevation angle is extremely low, the direct-path signal (a.k.a. target) will combine with its corresponding reflection from the earth (a.k.a. ghost). Sensing systems usually have limited angle resolution capability, so the presence of two closely-spaced signals could lead to low DOA estimation accuracy. This paper aims to address this issue by utilizing a super-resolution method based on the emerging technology of multiple-input multiple-output (MIMO) radar, which offer more degrees of freedom than traditional phased array counterparts. The proposed method specifically focuses on the MIMO configuration of synthetic impulse and aperture radars (SIAR) and involves two key steps. First, the targets are resolved in range, Doppler frequency, and azimuth angle in the matched filtering process. Next, the elevation information of the filtered signal is obtained using compressed sensing (CS) approaches. Our simulation results indicate that the proposed method achieves a higher performance in distinguishing low-angle targets from their corresponding ghosts, compared with traditional methods in terms of root mean squared error (RMSE) criterion.