用改进MMN的MLFMA分析外形隐身的多频减缩特性(英文)

为精确高效计算多极子模式数(MMN),提出了3个控制因子,详细研究了控制因子对多层快速多极子算法(MLFMA)的积分采样点数和计算精度的影响;基于控制因子,提出一种改进措施,可在保证精度的前提下,显著提高计算效率、有效降低内存。对3种飞行器,采用改进的MLFMA,分析了多频散射特性,发现飞行器外形在不同频率区域均可影响雷达散射截面(RCS)。研究了外形隐身布局和考虑隐身的常规布局的RCS多频减缩规律,结果表明,外形隐身在谐振区和高频区具有较大的RCS减缩效果,在瑞利区仍具有较弱影响;与吸波相比,外形隐身可产生较广的多频RCS减缩。以上结果可用于飞行器在多频段或全频段的隐身设计。     

飞行器RCS近场测试技术研究进展与工程应用

雷达散射截面(RCS)测试是隐身技术和目标特性研究的基础。无论是研究物体的电磁散射特性还是研制具有突防能力的隐身武器系统,RCS测试都具有非常重要的意义。通过RCS测试可以验证电磁散射计算的理论和方法,更重要的是,对部分飞行器目标进行电磁散射理论计算非常困难,而通过测试可以直观地获得目标的电磁散射特性数据,从而避开复杂的电磁仿真计算。与外场、紧缩场RCS测试方法相比,近年来得到广泛应用与发展的RCS近场测试方法在飞行器目标的散射特性测试方面具有效率高、成本低的优势。介绍了飞行器RCS测试评估方法,综述了国内外RCS近场测试技术研究的最新进展与工程应用实例,分析展望了飞行器RCS近场测试技术面临的机遇与挑战。     

铌掺杂ITO镀膜玻璃电磁散射特性试验

座舱玻璃镀膜是实现飞行器隐身技术的重要途径之一。利用雷达散射截面(RCS)均值增益研究铌掺杂ITO镀膜玻璃隐身性能;针对不同方块电阻的铌掺杂ITO镀膜玻璃,进行系列化RCS暗室测试,分析不同入射频率、极化方式的电磁散射特性。结果表明:方块电阻增大时电磁散射减弱,合适的方块电阻(小于40Ω/m~2)有利于实现座舱外形隐身,散射特性与金属接近,频率较高时,镜面散射波峰较窄。     

机载巡航导弹外形隐身改进的电磁散射影响

隐身技术是提高巡航导弹突防能力的重要技术手段，为分析外形隐身对巡航导弹电磁散射特性影响，建立了隐身、常规巡航导弹电磁模型，基于物理光学法和RCS减缩值，研究了外形隐身RCS曲线分布影响、频率响应特性、俯仰角响应特性。结果表明，外形隐身可大幅降低前后向散射特性，改变RCS散射波峰位置，使前后向曲线向内收敛；频率增加，前向均值和减缩值分别在-32 dBsm、25 dB左右振荡变化，其他角域RCS均值降低而减缩值增加；俯仰角变化较小时不影响散射特性，各角域RCS均值和减缩值呈振荡趋势，前向减缩值约为35 dB左右，后向俯仰角0度时最大。     

考虑旋翼调制影响的直升机RCS特性分析及评估

考虑旋翼调制的影响,建立了适合于直升机全机雷达散射截面(RCS)特性计算的“面元-边缘法”.兼顾计算效率和精度,在外形变化剧烈地区域,网格进行加密处理,并保证电磁网格密度和尺度满足雷达波波长大小的比例关系.以桨盘倾倒方式计入桨叶的挥舞和变距运动,采用准静态法模拟旋翼对全机RCS特性的影响.分析了某直升机RCS极化、姿态、频率响应特性,并根据直升机RCS和雷达探测距离关系,提出了4级预警机制和角域范围.研究表明:旋翼转动时全机RCS动态响应具有连续性和对称性,振荡区散射水平强,RCS幅值为-5~12dB ·m2;奇数片桨叶比偶数片桨叶的RCS减缩2~5dB ·m2,且有利于控制直升机RCS包络线和散射峰值的时域响应,增强雷达隐身性能.      

基于矩量法的机身截面电磁散射特性分析

机身截面隐身设计是飞行器外形隐身设计的一个重要的方面。设计＂凹曲面＂、＂凸曲面＂和＂平板曲面＂三种典型的隐身飞机机身截面轮廓,采用矩量法（MoM）计算三种轮廓的雷达散射截面（RCS）,并对表面电流密度分布进行研究。分析RCS随方位角的变化特性,比较各截面的隐身性能。分析结果表明：凹曲面和凸曲面机身可以有效降低侧向RCS,其中凸曲面的隐身效能更佳;平板曲面机身除正下方一个很窄的波峰外,侧向和下方RCS都很小,在对抗仰视雷达时具有很好的隐身性能。     

高超声速滑翔飞行器锐边化气动隐身一体化设计

隐身性能是影响高超声速武器作战效能的关键指标之一，为提高高超声速滑翔飞行器的生存及突防能力，以HTV-2飞行器为初始外形，引入锐边化设计思想，提出一种兼具良好隐身性能的气动外形。首先采用CFD数值模拟和高频近似算法，对初始外形气动特性及隐身特性进行评估。接着通过截取重要截面轮廓线，在轮廓线上均匀选取控制点。最终将离散点重构成三维外形，设计了一种锐边化飞行器外形。在此基础上计算评估了锐边化外形的升阻特性及雷达散射截面（RCS）。与原外形对比可知锐边化外形气动性能变化较小，气动力系数变化量不超过7%；同时在主要威胁区域（即俯仰角±30°、偏航角±60°角域）内飞行器的RCS均值显著降低，平均降幅超20%。此外为消除边缘绕射的影响，通过倒圆角的方式对锐边化外形的棱边进行了圆润化处理，实现了主要威胁区域内RCS均值的进一步减缩，平均降幅超过60%。此外进一步研究了在不同位置倒圆角及圆角半径对飞行器隐身特性的影响。结果表明在尾部截面倒圆角能较大程度改善飞行器的隐身特性，圆角半径与飞行器特征长度之比为1.35%时较佳。     

两种通用直升机雷达散射特性计算与分析

建立了两种通用直升机几何外形模型,采用物理光学法和等效电磁流法进行雷达散射特性计算分析.结果表明,两种通用直升机雷达散射水平较高,头向/尾向及侧向RCS分别达到数十和数百平方米;大曲率半径曲面机身比倾斜平面式机身散射强;可收放式起落架可以改善雷达隐身性能.本文结果对开展通用直升机雷达隐身设计研究具有重要的参考价值.     

座舱及进气道对某飞翼布局电磁散射影响

座舱和进气道对飞行器隐身性能有重要作用。为分析座舱及进气道的散射影响特性,建立了四种包含不同部件的电磁模型,结合物理光学法和雷达截面积(RCS)均值相对增值概念,研究了RCS曲线分布影响、俯仰角响应特性、频率响应特性。结果表明:考虑隐身设计的座舱和进气道不改变散射分布特性,RCS曲线分布特性相似;俯仰角增加,座舱影响较小,进气道、混合座舱和进气道前向、后向、周向角域相对增值震荡性递增,频率增加,座舱对电磁散射影响不大,进气道、混合座舱和进气道的前向、后向角域的相对增值震荡减小。座舱对电磁散射影响较小,前向相对增值位于-2.4～1 dB之间,进气道对电磁散射影响较大,前向相对增值为2～12 dB。     

基于CAD二次开发的飞行器隐身性能计算方法

在飞行器同雷达对抗时的不同威胁情况下,分析了在雷达仰视照射下飞行器的隐身性能。通过绘制雷达仰角图,得到了目标飞行器在某典型雷达照射下的暴露与隐身区域,从而量化了目标飞行器的隐身性能。通过CATIA二次开发技术实现了CAD模型的便捷修改,为优化外形隐身特性提供支持。最后通过一个具体算例验证种方法的效果,并说明方法具有实用意义。     

典型布局飞机电磁散射特性数值计算研究

电磁隐身对飞行器战场生存力具有重要影响,作战任务不同,对应的飞行器布局形式也不同,而飞行器布局形式会影响其电磁散射特性。建立四种典型布局形式和电磁模型,基于物理光学法,数值模拟不同布局飞行器的RCS曲线,并分析RCS分布特点;对常规和特殊布局模型,研究其电磁散射的频率响应特性。结果表明:飞机布局决定RCS分布形式,在前向角域内,布局A-1、A-2、B、C、D的电磁隐身性能呈震荡提高趋势,RCS均值从7.770 0dBsm震荡降低至-30.067 3dBsm,布局B的RCS均值为-10.434 7dBsm;而不同布局的后向和周向角域电磁隐身性能依次提高,后向RCS均值由常规布局的22.702 5dBsm缩减为-25.093 8dBsm,周向由7.039 1dBsm缩减为-15.137 3dBsm;在高频区域,频率增加对RCS曲线分布特点影响较小,但曲线震荡性更加明显,RCS算术均值降低。     

Electromagnetic Effects of Aircraft Wake-Active Feuillet Interaction

A mechanism by which an aircraft wake can interact strongly with the electromagnetic radiation present in an active elevated anomalous refractivity region (active feuillet) is analyzed. The aircraft wake structure, assumed to consist of twin contrarotating vortices plus entrained irrotational gas, trailing behind the wings of typical large aircraft is shown to be capable of descending a distance of approximately 3 wing span distances and attaining a length of the order of 10 km, prior to instability-induced disruption. The parcel of air such a descending coherent wake structure can convey into an active feuillet is demonstrated to alter significantly the local refractive index of the duct and induce substantial radiation spillage. The general characteristics of the electromagnetic radiation produced by this interaction process (i.e., scattering by diaphanous objects) is described.     

High-precision RCS measurement of aircraft’s weak scattering source

The radar cross section(RCS) of weak scattering source on the surface of an aircraft is usually less than 40 d Bsm.How to accurately measure the RCS characteristics of weak scattering source is a technical challenge for the aircraft's RCS measurement.This paper proposes separating and extracting the two-dimensional(2D) reflectivity distribution of the weak scattering source with the microwave imaging algorithm and spectral transform so as to enhance its measurement precision.Firstly,we performed the 2D microwave imaging of the target and then used the 2D gating function to separate and extract the reflectivity distribution of the weak scattering source.Secondly,we carried out the spectral transform of the reflectivity distribution and eventually obtained the RCS of the weak scattering source through calibration.The prototype experimental results and their analysis show that the measurement method is effective.The experiments on an aircraft's low-scattering conformal antenna verify that the measurement method can eliminate the clutter on the surface of aircraft.The precision of measuring a 40 d Bsm target is 3–5 d B better than the existing RCS measurement methods.The measurement method can more accurately obtain the weak scattering source's RCS characteristics.     

缝隙目标电磁散射特性试验

 通过对目标结构进行合理设计,可以在一定角域内显著减小雷达散射截面(RCS)。对飞行器表面常见锯齿缝隙的散射特性进行了研究。在微波暗室内对锯齿缝隙分别沿俯仰角变化、方位角变化的减缩效果进行测试。俯仰角变化时,锯齿缝隙有较好的减缩作用,以114°锯齿缝隙在试验中减缩效果最好。方位角变化时,对114°锯齿缝隙进行了多频段测试,并与相应直缝隙进行了对比研究,结果表明,通过选取合适的方位角角域,锯齿缝隙的减缩作用会随入射波频率的升高和仰角的增大而显著增强。结论可为高性能隐身飞行器外形隐身设计提供参考。     

Multi-frequency RCS Reduction Characteristics of Shape Stealth with MLFMA with Improved MMN

Three new control factors are presented for calculating the multipole mode number (MMN) efficiently and precisely. The effects of these control factors on the number of integral samples and the precision of multilevel fast multipole algorithm (MLFMA) are investigated. A new approach based on control factors which is proven to be able to improve the computational efficiency and reduce the needed memory significantly as well as ensuring the proper precision. For three aircraft models, the improved MLFMA is employed to analyze their multi-frequency scattering characteristics. It is found that aircraft shape can influence radar cross section (RCS) in different frequency zones. Both the multi-frequency RCS reduction characteristics of shape stealth aircraft and the conventional aircraft with stealth design taken into account are investigated, and the results show that shape stealth exhibits significant RCS reduction in the resonance and high-frequency zones, and with a weaker influence in the Rayleigh zone. Compared with radar absorbing material (RAM), shape stealth yields a wider multi-frequency RCS reduction. The above-mentioned results can be applied to stealth design for multiple frequencies or even for all frequencies.     

Study of RCS characteristics of tilt-rotor aircraft based on dynamic calculation approach

To study the Radar Cross-Section(RCS) characteristics of the tilt-rotor aircraft, a dynamic calculation approach that takes into account rotor rotation and nacelle tilt is presented.Physical optics and physical theory of diffraction are used to deal with the instantaneous electromagnetic scattering of the target. The RCS of the aircraft in the helicopter mode, fixed-wing mode and transition mode is analyzed. The results show that in the fixed-wing mode, the blade has a weaker deflection effect o...     

Influence of aircraft surface distribution on electromagnetic scattering characteristics

In this paper, two typical stealth aircraft concepts (wing fuselage blended and flying-wing) were designed. Then three gradually changed surface distribution models with the same plan-form for each concept were created. Based on the multilevel fast multipole algorithm (MLFMA), the vertical polarization transmitting/vertical polarization receiving (VV) and horizontal polariza-tion transmitting/horizontal polarization receiving (HH) radar cross section (RCS) characteristics were simulated with five frequencies between 0.1 and 1.0 GHz. The influences and mechanisms of aircraft surface distribution on electromagnetic scattering characteristics were investigated. The results show that for the wing fuselage blended concept, the VV RCS of this frequency range is higher than the HH RCS in most cases, while it is just the opposite for the flying-wing concept. As for the two aircraft concepts, the RCS levels of HH and VV both decrease with the frequency increasing, but the HH RCS has a faster downward trend. The surface distribution has little influ-ence on HH RCS characteristics. On the contrary, it has a significant impact on VV RCS charac-teristics, and the amplitude of the VV RCS increases with the surface thickness.     

基于数字虚拟飞行的民用飞机纵向地面操稳特性评估

针对民用飞机设计方案纵向地面操稳特性的评估需求,面向适航标准的要求,提出了一种基于数字虚拟飞行的评估方法。基于适航条例要求提出了纵向地面操稳特性的量化判定准则,建立了飞机的地面运动模型和驾驶员操纵模型,以实现起降等特定地面运行任务的数字虚拟飞行,最终依据数字虚拟飞行结果和判定准则对飞机设计方案的地面操稳特性做出评估。应用此方法研究了某大型运输类飞机的纵向地面操稳特性。数字虚拟飞行结果表明:前翻倾向的严重情况发生在起降过程的高速滑行段,主轮刹车引起的机身前翻倾向是显著的,起落架纵向定位参数设计以及飞行进近参数选择均会对飞机的纵向地面操稳特性产生影响。     

Tunnel/predictor display with two-axis control coordination and simplification

A longitudinal-lateral control coordination and simplification concept is considered for a tunnel/predictor display, which presents the command flight path and a specified future aircraft position in a 3-dimensional format to the pilot, for improving flight path control. A basic element of the proposed concept is the generation of common longitudinal-lateral transfer characteristics of the predictor-aircraft system for the crossover frequency region. Control coordination is supported by a dynamics similarity between the longitudinal and the lateral response characteristics of the predictor position in closed-loop pilot control actions. The control coordination and simplification concept is considered to support the pilot in manual flight path control, directed at an enhancement of his control performance and at a reduction of his workload. Results from pilot-in-the-loop simulation experiments support the theoretical findings and show the effectiveness of the proposed predictor concept with control coordination.