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DOA Estimation for Echo Signals and Experimental Results in the AM Radio-Based Passive Radar

The direction of arrival (DOA) of the target’s echo signal is extremely important for passive detection and tracking. However, it is a challenge to estimate the echo signal’s DOA due to the low signal-to-noise ratio of the echo signal and the serious masking effect. In this paper, a novel method is developed to estimate the DOA of the echo signal through enhancing the desired echo signal and attenuating the interference in range-Doppler domain before performing the DOA estimation. Firstly, the cross-ambiguity functions of the direct path signal and the received array signal are calculated. Then, they are combined to form a single-snapshot virtual array signal. Under certain conditions, the desired echo signal can be enhanced, and the interference can be attenuated simultaneously. After extending the single-snapshot virtual array signal to multi-snapshots, the conventional MUSIC approach can be performed, and the clutter interference can be suppressed significantly through subspace orthogonal meanwhile. Finally, the DOAs of echo signals as well as their corresponding Doppler shifts can be measured on a 2-D direction-Doppler map. The virtual array signal’s construction principle and the gain of echo signal are analyzed theoretically, and some experimental results are presented to verify the effectiveness of the proposed method.