Abstract
In a low-angle tracking situation, estimating the elevation angle is challenging due to the entrance of the multipath signals in the antenna’s main lobe. In this article, we propose two methods based on the extended Kalman filter (EKF) and frequency diversity (FD) process to estimate the elevation angle of a low-angle isolated target. In the first case, a simple weighting of the per-frequency estimates is obtained (termed WFD). Differently, in the second case, a matrix-based elaboration of the per-frequency estimates is proposed (termed MFD). The proposed methods are completely independent of prior knowledge of geometrical information and the physical parameters. The simulation results show that both methods have excellent performance and guarantee accurate elevation angle estimation in different multipath environments and even in very-low SNR conditions. Hence, they are both suitable for low-peak-power radars.
Highlights
For nearly half a century, researchers have been studying the problem of localizing low-elevation targets
One relies on simple weighting of per-frequency elevation estimates (WFD), whereas the other provides a matrix-based elaboration of the aforementioned estimates (MFD)
The SNR is set to 10 dB, and five operational frequencies for the Weighting-Based Frequency Diversity (WFD)
Summary
For nearly half a century, researchers have been studying the problem of localizing low-elevation targets. Specular and diffuse components reflected from the surface are received by the array and create a (ghost) image target below the surface These multipath components lead to an interfering effect in the elevation angle estimation process. Maximum likelihood (ML) is another basic parametric estimation method that handles the signal correlation without aperture loss [17] This method cannot separate the reflected signals and direct signal from each other in the low-angle situation and has high computational complexity. The computational complexity of the proposed methods is relatively low, and yet they present significant performance in tracking low-angle targets even for a low number of antenna array elements.
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