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Since the rotorcraft can easily be recognized by using the micro-Doppler (m-D) signature of rotor blades, the m-D effect induced by micro-motion dynamics plays an important role in target recognition and classification. However, the existing researches on the rotor blades pay little attention to the mechanism of the time-domain and time-frequency-domain flash phenomena. To comprehensively explain the flash phenomena from physics, the modeling of the rotor blades and the mechanism of the flash phenomena are studied in this paper. Firstly, for the rotor blades, the target cannot be represented as a rigid, homogeneous line nor several points. Taking the scattering coefficients and the interval of adjacent scattering points (the scattering point distribution on the blade) into consideration, the scattering point model of the rotor blade echo is established, and the influence of the scattering point distribution on the radar echo is analyzed as well. The detailed mathematic analysis and comparison results show that the conventional integral model of the rotor blade is only a special case of the scattering point model. Furthermore, In the case where the scattering point model is approximately equivalent to the conventional integral model, the critical interval of adjacent scattering points is deduced by mathematic analysis. Secondly, on the basis of the proposed model above, the physical mechanism of the time-domain and time-frequency-domain flash phenomena is studied from the viewpoint of the electromagnetic (EM) scattering. On the one hand, considering the EM scattering and scattering point distribution, the mechanism of the time-domain flashes is analyzed. Ideally, when the rotor blade is at the vertical position relative to the radar line of sight, i.e., at the flash time, the blade has the strongest echo. At this moment, the radar echo consists of echoes of all scattering points, thus inducing the time-domain flashes. At the non-flash time, the scattering points at the tip of blade and hub of rotor have stronger scattering intensities, so the echo is much weaker than that at the flash time. On the other hand, the time-frequency analysis and the cross range resolution are simultaneously used to analyze the mechanism of the time-frequency-domain flashes in the m-D signature. The m-D signature of the rotor blades consists of three parts: the time-frequency-domain flashes, the sinusoidal Doppler curves, and the zero-frequency band. At the flashes time, the Doppler frequency of adjacent scattering points cannot be distinguished, thus the m-D signature has the frequency band caused by all scattering points, i.e., the time-frequency-domain flashes appear. At the non-flash time, the sinusoidal Doppler curves and the zero-frequency band are caused by the scattering points at the tip of blade induced by the scattering points at the hub of rotor respectively. Finally, the simulation results about the scattering point model with the different intervals of adjacent scattering points show that the effectiveness of the proposed model and the correctness of theoretical analysis.
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Keywords:
- flashes /
- electromagnetic scattering /
- micro-Doppler /
- scattering points model
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[2] Chen V C, Tahmoush D, Miceli W J 2014 Radar Micro-Doppler Signature Processing and Applications (London: The Institution of Engineering and Technology) pp187-227
[3] Gao H W, Xie L G, Wen S L, Kuang Y 2010 IEEE Trans. Aero. Elec. Sys. 46 1969
[4] Lei P, Sun J P, Wang J, Hong W 2012 IEEE Trans. Geos. Remo. Sens. 50 3776
[5] Chen V C, Li F Y, Ho S S, Wechsler H 2006 IEEE Trans. Aero. Elec. Sys. 42 2
[6] Chen V C 2008 IET Sig. Proc. 2 291
[7] Wang T, Tong C M, Li X M, Li C Z 2015 Acta Phys. Sin. 64 210301 (in Chinese) [王童, 童创明, 李西敏, 李昌泽 2015 物理学报 64 210301]
[8] Chen P, Hao S Q, Zhao N X, Zhou J G 2013 Infrared and Laser Engineering 42 3259 (in Chinese) [陈鹏, 郝士琦, 赵楠翔, 周建国 2013 红外与激光工程 42 3259]
[9] Ye S B, Xiong J J 2006 Acta Aeronaut. Astronaut. Sin. 27 816 (in Chinese) [叶少波, 熊峻江 2006 航空学报 27 816]
[10] Jiang X W, Zhao Q J, Meng C 2014 Acta Aeronaut. Astronaut. Sin. 35 3123 (in Chinese) [蒋相闻, 招启军, 孟晨 2014 航空学报 35 3123]
[11] Huo K, Liu Y X, Hu J M, Jiang W D, Li X 2011 IEEE Trans. Geos. Remo. Sens. 49 1464
[12] Li J, Pi Y M, Yang X B 2010 J. Infra. Milli. Terahz. Waves 31 319
[13] Li P, Wang D C, Chen J L 2013 Sig. Image Video Proc. 7 1239
[14] Ji W J, Tong C M 2012 Acta Phys. Sin. 61 160301 (in Chinese) [姬伟杰, 童创明 2012 物理学报 61 160301]
[15] Zhang L X, Li N J, Hu C F, Li P 2009 Radar Target Scattering Characteristic Test and Diagnostic Imaging (Beijing: China Aviation Press) pp2-4 (in Chinese) [张麟兮, 李南京, 胡楚锋, 李萍 2009 雷达目标散射特性测试与成像诊断(北京: 中国航空出版社) 第 2-4 页]
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[1] Chen V C 2011 The Micro-Doppler Effect in Radar (Boston: Artech House) pp105-127
[2] Chen V C, Tahmoush D, Miceli W J 2014 Radar Micro-Doppler Signature Processing and Applications (London: The Institution of Engineering and Technology) pp187-227
[3] Gao H W, Xie L G, Wen S L, Kuang Y 2010 IEEE Trans. Aero. Elec. Sys. 46 1969
[4] Lei P, Sun J P, Wang J, Hong W 2012 IEEE Trans. Geos. Remo. Sens. 50 3776
[5] Chen V C, Li F Y, Ho S S, Wechsler H 2006 IEEE Trans. Aero. Elec. Sys. 42 2
[6] Chen V C 2008 IET Sig. Proc. 2 291
[7] Wang T, Tong C M, Li X M, Li C Z 2015 Acta Phys. Sin. 64 210301 (in Chinese) [王童, 童创明, 李西敏, 李昌泽 2015 物理学报 64 210301]
[8] Chen P, Hao S Q, Zhao N X, Zhou J G 2013 Infrared and Laser Engineering 42 3259 (in Chinese) [陈鹏, 郝士琦, 赵楠翔, 周建国 2013 红外与激光工程 42 3259]
[9] Ye S B, Xiong J J 2006 Acta Aeronaut. Astronaut. Sin. 27 816 (in Chinese) [叶少波, 熊峻江 2006 航空学报 27 816]
[10] Jiang X W, Zhao Q J, Meng C 2014 Acta Aeronaut. Astronaut. Sin. 35 3123 (in Chinese) [蒋相闻, 招启军, 孟晨 2014 航空学报 35 3123]
[11] Huo K, Liu Y X, Hu J M, Jiang W D, Li X 2011 IEEE Trans. Geos. Remo. Sens. 49 1464
[12] Li J, Pi Y M, Yang X B 2010 J. Infra. Milli. Terahz. Waves 31 319
[13] Li P, Wang D C, Chen J L 2013 Sig. Image Video Proc. 7 1239
[14] Ji W J, Tong C M 2012 Acta Phys. Sin. 61 160301 (in Chinese) [姬伟杰, 童创明 2012 物理学报 61 160301]
[15] Zhang L X, Li N J, Hu C F, Li P 2009 Radar Target Scattering Characteristic Test and Diagnostic Imaging (Beijing: China Aviation Press) pp2-4 (in Chinese) [张麟兮, 李南京, 胡楚锋, 李萍 2009 雷达目标散射特性测试与成像诊断(北京: 中国航空出版社) 第 2-4 页]
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