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In this paper, we consider the direction of arrival (DOA) estimation problem under the coexistence of noncircular and circular signals. By exploiting the difference between the circularity of noncircular and circular signals, a method is proposed, which estimates the DOAs of noncircular and circular signals separately. The maximum number of detectable directions by the proposed method is twice that by the MUSIC method. Furthermore, since the proposed method resolves noncircular and circular signals based on the circularity difference rather than the DOA difference, the proposed method performs well regardless of the DOA separation between noncircular and circular signals. Simulation results illustrate the effectiveness of the proposed method.

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Real-time radial velocity estimation is a key challenge for moving target imaging and location in current single-antenna synthetic aperture radar (SAR)-ground moving target indication systems. Since the conventional methods suffer from ambiguity, complexity realization, or heavy computation load for fast moving target motion estimation, this paper emphasizes the estimation efficiency by simple realization. An efficient Radon transform (RT) estimation is proposed to estimate the radial velocity of fast moving target by utilizing the geometry information, and much more geometry information is exploited to realize clutter cancellation, noise cancellation, and estimation error minimizing in the RT domain, which is not proposed by the others. With only two to four angles used to calculate rather than search for the radial velocity of moving targets, the proposed methods simplify the conventional range and angle (2-D) searching procedure into several time range (1-D) searching procedure efficiently. The theoretical and experimental analysis provides qualitative and quantitative evaluations into the effectiveness of the proposed methods. In the single-antenna SAR system, the proposed methods can estimate the radial velocity of fast moving target efficiently and accurately in high signal to clutter plus noise ratio scenarios.Index Terms-Efficient estimation, geometry information, radial velocity estimation, Radon transform (RT), synthetic aperture radar (SAR)-ground moving target indication (GMTI).