Abstract
Direction-of-arrival (DOA) estimation in multipath environment is an important issue for passive bistatic radar (PBR) using frequency agile phased array VHF radar as illuminator of opportunity. Under such scenario, the main focus of this paper is to cope with the closely spaced uncorrelated and coherent signals in low signal-to-noise ratio and limited snapshots. Making full use of the characteristics of moduli of eigenvalues, the DOAs of the uncorrelated signals are firstly estimated. Afterwards, their contributions are eliminated by means of spatial difference technique. Finally, in order to improve resolution and accuracy DOA estimation of remaining coherent signals while avoiding the cross-terms effect, a new beamforming solution based iterative adaptive approach (IAA) is proposed to deal with a reconstructed covariance matrix. The proposed method combines the advantages of both spatial difference method and the IAA algorithm while avoiding their shortcomings. Simulation results validate its effectiveness; meanwhile, the good performances of the proposed method in terms of resolution probability, detection probability, and estimation accuracy are demonstrated by comparison with the existing methods.
Highlights
Passive bistatic radar (PBR) exploiting illuminators of opportunity as uncooperative transmitters has become an emerging technology because it allows target detection and localization with advantages such as low cost, covert detection, and low vulnerability to electronic jamming [1, 2]
It is worth pointing out that the two uncorrelated signals are set as θ = −30∘ and = 0∘, which come from the same direction with the two groups of coherent signals; in the first group of coherent signals, the two signals are closely spaced in the mainlobe
For our method, when dealing with uncorrelated and coherent signals, we combine the advantages of spatial difference method and iterative adaptive approach (IAA) algorithm and propose a novel IAA-based beamforming solution with respect to the improved covariance matrix, which can effectively improve the performance of resolution and accuracy in DOA estimation
Summary
Passive bistatic radar (PBR) exploiting illuminators of opportunity as uncooperative transmitters has become an emerging technology because it allows target detection and localization with advantages such as low cost, covert detection, and low vulnerability to electronic jamming [1, 2]. The problem, is that the decorrelation via spatial smoothing technique is acquired at the cost of the reduction in array aperture, which would further increase the width of mainlobe and make the resolution worse These methods cannot resolve the uncorrelated and coherent signals that are in the same direction. Since [20,21,22,23] eliminate the contributions of uncorrelated signals by constructing a difference matrix, which encounter the problem of crossterms effect and may yield wrong DOA estimates when the number of snapshots is small, the method introduced in [24, 25] makes full use of the property of the moduli of eigenvalues to resolve the uncorrelated signals from the coherent signals. To eliminate the cross-terms effect while improving the resolution and accuracy of DOA estimation of the remaining coherent signals, a new IAA-based beamforming solution is conducted on a reconstructed covariance matrix. Simulation results validate the better performance of the proposed method by comparison with the existing algorithms
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