Analysis of dynamic electromagnetic scattering characteristics of compound coaxial helicopter
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摘要:
在复合式共轴直升机高速发展的趋势下，为了探索其电磁散射规律以更好地进行隐身设计和目标识别工作，系统开展了复合式共轴直升机动态电磁散射特性仿真分析研究。构建能够表征耦合反转双旋翼和尾推桨旋转复杂运动特征的动态时变电磁计算网格；采用高频方法计算共轴直升机的动态雷达散射截面（RCS），揭示了双旋翼和尾推桨对全机动态RCS的贡献与影响机理，为直升机重点威胁方位上动、静部件RCS减缩的主次地位划分奠定了基础；并总结了旋转部件微多普勒的变化规律和关联性，提出了识别与判断复合式共轴直升机机动意图的一种思路。分析表明：双旋翼和尾推桨的存在使全机RCS呈现动态周期性振荡特征，振荡幅度与非旋转部件的静态RCS大小相关；后掠桨尖会引起时间上滞后于桨叶内段的微多普勒闪烁带，滞后时间取决于桨叶转速和桨尖后掠角度；在任一雷达视线角下，双旋翼和尾推桨的最大微多普勒频移为一组确定数值，分析两者的微多普勒走势，可以准确识别直升机飞行姿态变化，进而推断其机动意图。
Abstract:Under the trend of rapid development of compound coaxial helicopter, simulation analysis of dynamic electromagnetic scattering characteristics of compound coaxial helicopter was carried out systematically to explore its electromagnetic scattering law for stealth design and target recognition. A method of dynamic time-varying electromagnetic computing mesh that can characterize the coupled rotational motions of coaxial-rotor and tail rotor was constructed. The dynamic radar cross section (RCS) of the coaxial helicopter was calculated by the high frequency methods, and the contribution and influence mechanism of the coaxial-rotor and the tail rotor to the dynamic RCS of the whole helicopter were revealed, which layed a foundation for the sequence division of the RCS reduction of the dynamic and static components in the key threat azimuth of the helicopter. The change law and correlation of micro-Doppler of rotating parts were summarized, and an idea of identifying and judging the maneuvering intention of compound coaxial helicopter was proposed. The analyses showed that, in the existence of coaxial-rotor and tail rotor, the RCS of the whole aircraft exhibited dynamic periodic oscillation characteristics, and the oscillation amplitude was related to the static RCS of non-rotating components. The backward-swept blade tip could cause a micro-Doppler scintillation band that lagged behind the inner section of the blade in time, and the lag time depended on the blade rotation speed and the sweep angle of the blade tip. At any radar incident angle, the maximum micro-Doppler frequency shift of the coaxial-rotor and the tail rotor was represented by a set of determined values. By analyzing the micro-Doppler trend of these two, the flight attitude change of the helicopter can be accurately identified, and then its maneuvering intention can be inferred.
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图 4 俯仰角为0°，方位角为0°的全机动态RCS特性
Figure 4. Dynamic RCS of whole helicopter at 0° azimuth angle, 0° pitch angle
图 5 俯仰角为0°，方位角为42°的全机动态RCS特性
Figure 5. Dynamic RCS of whole helicopter at 42° azimuth angle, 0° pitch angle
图 6 俯仰角为0°，方位角为90°的全机动态RCS特性
Figure 6. Dynamic RCS of whole helicopter at 90° azimuth angle, 0° pitch angle
图 7 俯仰角为0°，方位角为180°的全机动态RCS特性
Figure 7. Dynamic RCS of whole helicopter at 180° azimuth angle, 0° pitch angle
图 8 俯仰角为−30°，方位角为0°的全机动态RCS特性
Figure 8. Dynamic RCS of whole helicopter at different 0° azimuth angle, −30° pitch angle
图 9 俯仰角为30°，方位角为0°的全机动态RCS特性
Figure 9. Dynamic RCS of whole helicopter at different 0° azimuth angle, 30° pitch angle
图 11 雷达连续扫射下旋转部件最大微多普勒频移变化曲线
Figure 11. Maximum micro-Doppler frequency shift curve of rotating parts under radar continuous scanning
表 1 共轴直升机主要参数
Table 1. Main parameters of the coaxial helicopter
参数 数值 机身高度/m 不带旋翼 3.1 带旋翼 4.8 机身长度/m 不带旋翼 14.9 带旋翼 15.7 机身宽度/m 2.6 垂尾宽度/m 5.4 双旋翼半径/m 7.2 双旋翼转速/（rad/s） 25.97 尾推桨半径/m 1.39 尾推桨转速/（rad/s） 129.85 
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