澳洲军事专家库珀：歼20原型机隐身性能初步评估

本文是由澳大利亚军事专家卡罗·库珀和迈克尔·佩洛西联合撰写的一篇关于歼20隐身性能的初步评估的军事技术论文。主要介绍了歼20的外形特点和隐形飞机的一些基本知识，包括隐身材料，并提出了估算RCS的方法。进行具体的实验过程和图表分析，以及对歼20隐身性能的数值结果，并做以总结。附录部分没有进行翻译，其中的一些专业术语、理论、概念等均在译文中夹杂介绍。A Preliminary Assessment of Specular Radar Cross Section Performance in the Chengdu J-20 Prototype
成都歼20原型机隐身性能初步评估

Air Power Australia Analysis 2011-03
4th July 2011

A Monograph by 
Dr Michael J Pelosi, MBA, MPA,
Dr Carlo Kopp, SMAIAA, SMIEEE, PEng

Text, computer graphics © 2011 Michael Pelosi, © 2011 Carlo Kopp

澳大利亚空中力量分析 2011-3

2011年7月4日论文由 

迈克尔·J·佩洛西 博士/MBA/MPA

卡罗·库珀 博士/MSAIAA/SMIEEE/PEng

文字，电脑绘图©2011 迈克尔·佩洛西，© 2011 卡罗·库珀

First public flight of the Chengdu J-20 prototype, 11th January, 2011 . The shaping design of the J-20 presents no fundamental obstacles to its development into a genuine Very Low Observable design (Chinese Internet).2011年1月11日，成都歼20原型机首次公开试飞。歼20的造型设计表明，不会对其改进型的超低可探测性（简称VLO，也就是隐身技术Stealth Technology）。设计造成实质影响。
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Abstract

摘要

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This study has explored the specular Radar Cross Section of the Chengdu J-20 prototype aircraft shaping design. Simulations using a Physical Optics simulation algorithm were performed for frequencies of 150 MHz, 600 MHz, 1.2 GHz, 3.0 GHz, 6.0 GHz, 8.0 GHz, 12.0 GHz, 16.0 GHz and 28 GHz without an absorbent coating, and for frequencies of 1.2 GHz, 3.0 GHz, 6.0 GHz, 8.0 GHz, 12.0 GHz, 16.0 GHz with an absorbent coating, covering all angular aspects of the airframe. In addition, the performance of a range of Chinese developed radar absorbers was modelled, based on a reasonable survey of unclassified Chinese research publications in the area. None of the surveyed materials were found to be suitable for use as impedance matched specular radar absorbers. Modelling has determined, that if the production J-20 retains the axisymmetric nozzles and smoothly area ruled sides, the aircraft could at best deliver robust Very Low Observable performance in the nose aspect angular sector. Conversely, if the production J-20 introduces a rectangular faceted nozzle design, and refinements to fuselage side shaping, the design would present very good potential for  robust Very Low Observable performance in the S-band and above, for the nose and tail aspect angular sectors, with good performance in the beam aspect angular sector. This study has therefore established through Physical Optics simulation across nine radio-frequency bands, that no fundamental obstacles exist in the shaping design of the J-20 prototype precluding its development into a genuine Very Low Observable design.
本课题探讨了成都歼20原型机隐身性能的造型设计，运用物理光学仿真算法在没有隐形涂层情况下分别进行了频率为150兆赫兹、600兆赫兹、1.2千兆赫兹、3.0千兆赫兹、6.0千兆赫兹、8.0千兆赫兹、12.0千兆赫兹、16.0千兆赫兹和28千兆赫兹的模拟，以及在敷设了隐身涂层的情况下，进行了频率为1.2千兆赫兹、3.0千兆赫兹、6.0千兆赫兹、8.0千兆赫兹、12.0千兆赫兹和16.0千兆赫兹的模拟，覆盖了整个机身的角度位面。此外，中国研制的雷达吸波材料的一系列性能已经建模，基于一份非机密的中国该领域研究发行的调查报告。调查表明，材料不适合作为匹配镜面雷达吸收剂的阻抗。在模型已经确定的情况下，如果歼20的生产保留轴对称喷口和符合面积律的平滑截面，飞机最多只能为机头部分提供强劲的超低可探测性能。反之，如果歼20的生产引进矩面喷口设计，改进侧面机身造型，强劲的超低可探测性能将会在S波段及以上范围展现出巨大的潜力，机头部分和机尾以及侧向也会有良好的性能。本课题是通过物理光学模拟穿越九个无线电波段，在歼20原型机的外形设计不存在根本缺陷的情况下，确保改进型达到真正的超低可探测设计。

注释：Radar Cross Section（RCS），雷达散射截面是目标的一种折算面积，用来度量在雷达波照射下所产生的回波强度大小。RCS越小，说明反射越小，越不容易被发现，从而达到“隐身”的效果。RCS减缩有两种途径：一种是外形隐身，通过改变机身造型，把雷达波反射到雷达无法接收的方向上；一种是材料隐身，通过对机身敷设吸波涂层，把雷达波的能量损耗掉。通常外形隐身占到整个RCS减缩的90%左右，也就是说，衡量一架飞机隐身性能的优劣，主要看造型设计是否合理。同时，造型设计关乎到飞机的气动布局，所以如何兼顾隐身和气动的性能，成为了隐身设计的一大课题。
阻抗匹配：当飞行器受到雷达波的照射时，飞行器本身将产生一个散射场，如果雷达吸波材料的阻抗负载合适，则可以使阻抗产生的电磁场与飞行器产生的散射场的场强矢量振幅相当，相位相反，从而相互干涉，使两个场的合成场强减弱，降低飞机的RCS。
·Introduction
·J-20 Prototype Very Low Observable Airframe Shaping Design Features 　　Chinese Absorbent Materials Technology
·Radar Cross Section Simulation Method / Simulator Design and Capabilities 　　Aircraft Model Features and Limitations　　What the Simulation Does Not Demonstrate　　What the Simulation Does Demonstrate
·Specular Radar Cross Section Simulation Results 　　Analysis of Shape Related Specular Radar Cross Section　　Analysis of Specular RCS with a Representative RAM Coating
·Conclusions
·Endnotes, References and Bibliography:
·Annex A Scales, Bands, Geometries, and Representative Threats
·Annex B Basic Concepts in Absorbent Coatings Technology
·Annex C Axisymmetric Nozzle RCS Performance
·Annex D Viewing RCS Plots
·Annex E Glossary of Terms·介绍
·歼20原型机超低可探测机身外形设计特点
     中国的吸波材料技术
·RCS的模拟方法/模拟设计和功能
     飞机模型的特点和局限性
     什么是非论证模拟
     什么是论证模拟
·镜面RCS的模拟结果
     外形RCS的相关分析
     涂抹典型雷达吸波材料的隐身性能分析
·结论
·附注、参考文献和参考书目：
·附录一 减缩、波段、几何和典型威胁
·附录二 吸收材料技术的基本概念
·附录三 轴对称喷口的隐身性能
·附录四 查看RCS图解
·附录五 术语
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                                                                    Introduction 介绍-------------------------------------------------------------------------------There has been extensive media speculation about the Radar Cross Section [RCS] of the J-20 stealth fighter, since the PLA-AF first exposed the prototype to the public in late December, 2010. Sadly much of this speculation has no valid scientific basis, yet appears to be regarded seriously enough to have influenced public statements by numerous senior officials in Western defence departments.自从2010年12月份中国空军首次公开透露了原型机以来，很多媒体都在猜测歼20隐形战斗机的RCS。这种猜测虽然没有科学依据，却似乎被认为是一份足以影响到许多西方国防部门高级官员的公开声明。
Performing a full assessment of the RCS of any Low Observable [LO / -10 to -30 dBSM, Refer Table A.1] or Very Low Observable [VLO / -30 to -40 dBSM, Refer Table A.1] aircraft is not a trivial task, as due consideration needs to be given to all major and minor RCS contributors in the design.进行任何低可探测（LO / -10到-30 dBSM，参见 表格A.1） 或者超低可探测（VLO / -30到-40 dBSM，参见 表格A.1）飞机的全面评估不是一项简单的任务，需要考虑到设计之中所有主要和次要的RCS贡献。
注释：RCS用σ（Sigma）表示，常用单位为㎡（平方米）或dBSM（分贝平方米），公式为σ=4π *（目标处单位立体角内的散射功率/目标处单位面积上的入射功率），两个单位之间的转换关系是：1000㎡=30dbsm，100㎡=20dbsm，10㎡=10dbsm，1㎡=0dbsm，0.1㎡=-10dbsm，0.01㎡=-20dbsm，也就是说，如果RCS的值是0分贝，那么目标的有效照射面积便是1平方米。（显然，目标的真实面积肯定比1平方米大的多）RCS的“贡献”越大，其值越高。
Moreover, such an assessment, if it is to be useful, must consider the RCS from a range of different angular aspects, this encompassing azimuthal sectors and also elevation or depression angles characteristic of the surface and airborne threat systems the LO/VLO design is intended to defeat [Refer Figures A.3 and A.4].另外，要使评估有效，必须考虑一系列不同角度位面的隐身效果，包括旨在挫败LO/VLO设计的地面和空中威胁系统在各个方位面以及俯仰角的典型特征。（参见 图表A.3和A.4）（威胁系统指能够搜索、捕获、攻击飞机的雷达、导弹等军事设施）
The assessment of RCS must also be performed at the operating wavelengths typical of the surface and airborne threat systems the LO/VLO design is intended to defeat [Refer Table A.2].对RCS的评估也必须建立在旨在挫败LO/VLO设计的地面和空中威胁系统的工作波长典型特征之下。（参见 表格A.2）

注释：RCS的大小取决于：目标的物理特性（电特性）、目标的几何特性、目标被雷达波照射的方位、入射波的波长、入射场极化方式和接受天线的极化方式。这里先谈谈几何形状对RCS的影响。1、角反射器：雷达波会在两三个平面相交构成的尖锐折角上折射放大，产生很强的回波信号，尤其是正交直角。2、凹腔效应：雷达波在凹腔内经过多次反射、叠加放大之后返回雷达。3、平行原则：对飞机上的边缘进行平行设计，从而将照射的雷达波集中反射到雷达接收不到的方向。（下文中提到的回波的主瓣和副瓣，就是指把电磁波集中反射的几个方向）4、隐藏强散射源：比如弹仓内挂武器或者S型进气道设计，防止雷达波直接照射发动机叶片。5、用一个部件遮挡住另一个强散射部件，比如背负式进气道（进气道在机身上方）或者用垂尾来遮挡尾喷口。6、结构细节处理：包括对铆钉、台阶等处理，防止次级散射；以及把舱门盖口的边缘和缝隙设计成锯齿形状，这样一来可以加剧散射，降低回波方向的强度。
Definitions of these and other terms employed in this document are summarised in Annex E. Reference data for RCS scales, radio-frequency bands, engagement geometries,  and representative threat systems are summarised in Annex A.这些定义和文章中引用的其它术语见附录E。参考资料来源于RCS减缩、无线电波段、接触几何和典型威胁系统见附录A。
If the RCS assessment does not consider angular and wavelength dependencies properly, it will be almost meaningless, in terms of providing a means of determining or estimating the survivability of the LO/VLO design. The common practice of providing a single RCS value for a single aspect at a single frequency yields little information about the actual effectiveness of the design. Such a single point figure permits at best a detection range estimate for a known radar operating at the specified wavelength and aspect.
如果RCS评估不考虑角度和波长的适当关联，只是按照某种方法来确定或估算LO/VLO设计的生存能力，这是毫无意义的。通常在单一频率下的单个面给定一个单一的RCS值，几乎不能印证真实的设计效果。这种单个点阵图所表示的最大范围只是一个已知雷达在规定波长和位面的探测距离。
The PLA's J-20 prototype is an important development in terms of grand strategy, as well as technological strategy, and basic technology. It shows that PLA thinking at the strategic level is focussed on defeating opposing IADS [Integrated Air Defence System] and fighter forces. In the domain of technological strategy, it shows a robust grasp of the limitations of Western technology deployed in

Asia. In terms of basic technology, it shows that China's academic research and industrial base has mastered advanced LO/VLO shaping techniques.解放军的歼20原型机是国家战略、科技战略和基础技术方面的重大进步。这表明了解放军在战略层面的考量已经对准了挫败IADS（综合防空系统）和空军力量。在科技战略领域，表明了PLA强有力地抓住了西方科技在亚洲部署的局限性。在基础技术方面，表明了中国的学术研究和工业基地已经掌握了先进的LO/VLO成形技术。
The intent of this study is to perform a preliminary assessment of the RCS of the J-20 prototype, to establish the potential of the aircraft to be fully developed as an LO/VLO combat asset.本课题的目的是对歼20原型机的RCS进行初步评估，以确定飞机是否具有成为最先进的低可探测/超低可探测战斗王牌的潜能。
The assessment cannot be more than preliminary for a number of good reasons:
   1. The final airframe shaping remains unknown, and changes may arise through the development cycle, to improve
       aerodynamic performance, operational characteristics, and LO/VLO performance; 
   2. The state of Chinese Radar Absorbent Materials (RAM), Radar Absorbent Structures (RAS) and radar absorbent
       coatings technology is not well understood in the West; 
   3. The state of Chinese technologies for sensor aperture (radar, EO, passive RF) structural mode RCS reduction is not well 
       understood in the West; 
   4. The state of Chinese technologies for RCS flare spot reduction, in areas such as  navigation/communications antennas, 
       seals, panel joins, drain apertures, cooling vents, and fasteners is not well understood in the West.
评估只能是最低级别的几个理由：
1、最终机身造型仍然未知，研发环节可能出现变数，进一步提高空气动力性能、操作特点和LO/VLO性能；
2、西方并不十分清楚中国的雷达吸波材料（RAM），雷达吸波结构（RAS）和雷达吸波涂层技术。
3、西方并不十分清楚中国的传感器（雷达、光电、被动射频）孔径的结构模式和RCS减缩技术。
4、西方并不十分清楚中国的RCS光斑减缩技术，还有导航/通信天线、封条、面板连接、排水孔、散热孔和紧固件等。

注释：雷达吸波材料（RAM）是照射到飞机上的电磁能量被吸收并转化为热能，使反射出去的电波能量越少越好。雷达吸波材料分为涂敷型吸波材料与结构型吸波材料两种。雷达吸波结构（RAS）是一种结合飞机外形的曲面和部位，由RAM、透波材料及其它材料构成独特的吸波-承载复合结构。也就是说，一部分复合材料既可以起到吸波的作用，又可以充当承载和减重的作用。
Achievement of credible LO or VLO performance is the result of a design having intended RCS characteristics in all of these 
categories.The relative importance of the respective categories should be discussed.
在所有类别中，使其具有RCS特性的设计，是为了达到可靠的LO/VLO性能。我们要讨论的是相对重要的分类。
Sound airframe shaping is a necessary prerequisite for good LO or VLO performance. If shaping is poor, no amount of credible materials application and detail flare spot reduction will overcome the RCS contributions produced by the airframe shape, and genuine VLO performance will be unattainable.合理的机身造型是良好的LO/VLO性能的先决条件。如果造型很差，即便使用再可靠的材料和细微光斑减缩，也无法比拟机身外形对于减少RCS的贡献。
If airframe shaping is sound, then careful and well considered application of Radar Absorbent Materials (RAM), Radar Absorbent Structures (RAS), radar absorbent coatings, aperture RCS reductions, and minor flare spot reductions techniques will yield a VLO design.如果机身造型合理，只要谨慎地使用雷达吸波材料（RAM）、雷达吸波结构、雷达吸波涂层、孔径RCS减缩和较为次要的光斑减缩技术，就会凸显超低可探测设计。
As a result, modelling of the shape related RCS contributions of any VLO design is of very high value, as it determines not only whether the aircraft can achieve credible VLO category performance, but also where the designers will be investing effort in RAS, RAM and coating application to achieve this effect.因此，与外形建模有关的任何VLO设计对于RCS贡献都具有非常高的价值，因为这不仅决定了飞机是否能达到可靠的隐身性能，同时也会使设计师致力于研究RAS、RAM和涂层的应用所产生的效果。
This paper will focus mostly on shape related RCS contributions, due to the uncertainties inherent in estimating the performance of unknown technologies for RAS, RAM, coatings, aperture RCS reductions, and minor flare spot reduction. Where applicable, reasonable assumptions will be made as to the performance of absorbent material related RCS reduction measures. Some tentative modelling of published Chinese RAM coatings will be performed.本文将重点关注与外形相关的RCS贡献，对RAS、RAM、涂料、孔径RCS减缩和次要的光斑减缩等未知技术性能进行估算时，其固有的不确定因素是无法避免的。在适当情形下，合理的假设可以推算出RCS减缩措施相关的吸波材料的性能。同时，对一些中国已公开的RAM涂料的实验性模拟也会展开。
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J-20 Prototype Very Low Observable Airframe Shaping Design Features

歼20原型机超低可探测机身造型设计特点

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The J-20 prototype designs displays a number of VLO design features, generally based on design rules developed for and employed in the construction of United States VLO combat aircraft. These display a good theoretical and practical understanding of the VLO design rules developed by US researchers in industry and US government research laboratories, between 1975 and 2000.歼20原型机的设计显示了一些VLO的设计特点，在常规设计规则的基础上进行开发，同时借鉴了美国VLO战斗机的制造工艺。这些表明了对VLO设计规则有着良好的理论和实践中的理解，VLO设计规则是在1975年至2000年，由美国行业研究和美国政府研究实验室开发而成的。
Overall, the stealth shaping of the J-20 prototype design is without doubt considerably better than that seen in the Russian T-50 PAK-FA prototypes and, even more so, than that seen in the intended production configuration of the United States' F-35 Joint Strike Fighter.总的来说，歼20原型机的隐身造型设计无疑大大优于俄罗斯的T-50五代机，甚至是美国计划投产的F35联合攻击战斗机。
The J-20 design appears to be mostly constructed around the stealth shaping design rules employed in the US Air Force F-22A 
Raptor:歼20的设计似乎大多都是围绕美国空军的F22的隐形造型设计规则：
1.The chined J-20 nose section and canopy are close in appearance to the F-22, yielding similar specular RCS performance in a 
mature design. 1、歼20的机头部分和座舱罩和F22的外观接近，设计十分成熟，所以二者的隐身性能十分接近。
注释：飞机各个部位的主要散射源和散射机理。头向——座舱、雷达舱和进气道的凹腔效应；正侧向——机身与垂尾的镜面反射、机翼与机身以及平尾与垂尾的角反射；后向——喷口的凹腔效应；斜侧向——机翼和平尾前后缘的边缘绕射；其它——外挂物散射、缝隙绕射、尖点绕射、表面波绕射等。
歼20机头部分的RCS减缩。其中，座舱罩采取了金属镀膜处理技术（光电设计），既遮挡住了雷达波，同时又不会影响可见光的照射，为飞行员提供了良好的视野。而进气道的入口斜切并设计成S型进气道，不会使雷达波直接照射到发动机叶片而产生强烈的散射源；同时内壁敷设吸波材料，雷达波在进气道来回反弹吸波，损耗功率。
2.The J-20 trapezoidal edge aligned engine inlets are closest to the F-22, though they appear to be larger and employ an F-35 
style DSI (Diverterless Supersonic Inlet) design, obviously intended to improve on F-22 inlet leading edge signature. 2、歼20梯形进气口的对齐方式与F22十分接近，但他们似乎更多地采用了F35的DSI（无附面层隔道超音速进气道 ）设计风格，显然他们打算改进F22的进气口边缘的信号特征。
3.The J-20 wing fuselage join, critical for beam and all aspect stealth, is in shaping and angle very similar to the F-22, and 
clearly superior to both the T-50 PAK-FA prototypes and the F-35 Joint Strike Fighter. 3、歼20的翼身融合在造型和角度上都与F22十分类似，对侧向和全向的隐身起到了重要作用，明显优于T50五代机和F35联合攻击战斗机。
注释：翼身融合，机翼和机身结合处的外形，无论取纵向截面或横向截面，其轮廓线都是连续曲线。消除了垂直侧面机身与机翼的角反射器效应。
4.The J-20 flat lower fuselage is optimal for all aspect wideband stealth, and emulates the F-22 design closely. It can produce a 
significant ground bounce return in some geometries, especially at lower altitudes, or angles approaching the normal.
4、歼20平滑的机身底部很好地模仿了F22的设计，是全频隐身的最佳选择。在一些地方，尤其是低空和靠近法线的角度，可以产生明显的地面反弹。
5.Planform alignment of the J-20 shows exact angular alignment between canard and delta leading edges, and exact crossed (starboard to port, port to starboard) angular edge alignment between canard and delta trailing edges. Leading edge sweep is ~43°, clearly intended for efficient supersonic flight. 5、歼20的平面对齐方式显示，鸭翼和三角翼的前缘对齐，鸭翼和三角翼对侧（右舷对左舷，左舷对右舷）后缘对齐。前缘后掠角约43度，显然倾向于超音速飞行。

注释：鸭式布局，是一种非常适于超音速空战的气动布局，座舱两侧有两个较小的三角翼（鸭翼），后边是一个较大的三角翼（主翼）。鸭式布局的优点是通过较小的鸭翼达到与水平尾翼同样的操纵效能，增强了低空的机动性。缺点是鸭翼一旦转动，角度就会变化，从而影响隐身效果。歼20的鸭翼采用隐身涂料和吸波/透波复合材料，估计对RCS的影响不会很大。
6.The J-20 nose and main undercarriage, and cheek weapon bay doors employ C-band through Ku-band optimised edge serration technology, based on F-117A and F-22 design rules. 6、歼20的机头、主起落架和两侧武器舱门采取了C波段到Ku波段的边缘锯齿优化技术，设计规则来自F117和F22。
7.The aft fuselage, tailbooms, fins/strakes and axi-symmetric nozzles are not compatible with high stealth performance, but may only be stop-gap measures to expedite flight testing of a prototype. Performance is notably poorer in the H polarisation.
7、后机身、尾段、安定翼/边条和轴对称喷口的设计不利于隐身，但也可能是为了加快原型机飞行试验的权宜之计。特别是在电磁波的H方向的隐身性能较差。
8.The airframe configuration and aft fuselage shape would be compatible with an F-22A style 2D TVC nozzle design, or a non-TVC rectangular nozzle designed for controlled infrared emission patterns and radio-frequency stealth. Infrared signature will be influenced by other considerations, especially engine bypass ratio. 
8、如果使用二维推力矢量喷口设计或非推力矢量抑制红外和无线电隐身的喷口设计，机身结构和后机身外形将会与F22风格一致。红外特征还取决于其它因素，尤其是发动机涵道比。
注释：涵道比（bypass ratio），即涡轮发动机外涵道与内涵道空气流量的比值。内涵道的空气流入燃烧室与燃料混合，燃烧做功，外涵道的空气不进入燃烧室，而是与内涵道流出的燃气相混合后排出。外涵道的空气只通过风扇，流速较慢，且是低温，内涵道排出的是高温燃气，两种气体混合后降低了流速与温度，能够降低噪声，增加推力。
9.The choice of all moving slab stabilators and canards will impact RCS at deflection angles away from the neutral position. If large control deflections are produced in flight regimes other than close combat manoeuvring, the specular RCS of the all moving slab controls would need to be considered.
9、全动平尾和前翼在偏转角远离中间时会对RCS造成影响。与近距离作战不同，一般飞行状态下的大幅度偏转对RCS造成的影响必须考虑在内。
A qualitative assessment of the J-20 prototype clearly shows that the design has the potential for VLO capability, certainly in the very important forward hemisphere.歼20原型机的质量评定清晰地表明设计拥有潜在的VLO性能，特别是在非常重要的前方半球。
Available imagery from similar or identical aspects permits direct comparisons between the J-20 and the United States F-22A and F-35 designs.下面用图片从相似或相同的角度对歼20和美国的F22、F35加以直观的比较。

Elevated head on view of J-20 prototype showing the trapezoidal edge aligned inlet geometry, combining features of the F-22A Raptor and F-35 JSF inlet. Both aircraft share shallow wing/fuselage join angles and a flat lower fuselage .20的前端高点视图，进气口呈梯形对称分布，综合了F22和F35的技术特点。机翼与机身和平滑机腹的连接一气呵成。
Head on view of F-22A Raptor showing the trapezoidal edge aligned inlet geometry (US Air Force).F22的前端视图，进气口呈梯形对称分布。
The shaping features of the inlet area and unique lower fuselage are prominent on this image of F-35A SDD prototype AA-1 (Image via Air Force Link)F35的进气口造型特点和独一无二的机腹在这张图上表现地十分突出。
This J-20 view shows the chine geometry, and generous use of X-band serrations on the undercarriage doors (Chinese Internet)这张图显示了歼20的机脊形状，和大量应用在起落架仓门上的X波段锯齿。
Ventral view of F-22A Raptor with undercarriage extended (US Air Force).F22底盘延展的腹鳍视图。
F-35 JSF SDD airframe in flight showing chine angles and upper fuselage curvature (U.S. Air Force photo).飞行中的F35机脊角度和机身上部的曲率。
Ventral view of J-20 prototype showing the flat lower fuselage, flat facet fuselage sides, and shallow join angle between the wings, canards and fuselage sides. The aft ventral strakes are undesirable from an RCS perspective (Chinese Internet).歼20的腹鳍视图，平滑的机腹和机身两侧，机翼、鸭翼和机身两侧的连接一气呵成。尾部的腹鳍板对RCS性能有所影响。

Ventral view of F-22A Raptor showing the flat lower fuselage, flat facet fuselage sides, and shallow join angle between the wings, horizontal tails and fuselage sides (U.S. Air Force photo).F22的腹鳍视图，平滑的机腹和机身两侧，机翼、水平尾翼和机身两侧的连接一气呵成。（美国空军图片）
Ventral view of F-35A SDD aircraft showing the deeply sculpted lower fuselage, doubly curved fuselage sides, and  steep angle multiple step join between the wings and fuselage sides (U.S. Air Force photo).F35的腹鳍视图，深褶的机腹，双重弯曲的机身两侧，机翼和机身两侧以多阶梯状的生硬折角连接。
Aft view of J-20 prototype showing the serrated axi-symmetric nozzles, modelled on the F-35 JSF design, the strakes and all moving tails, and deflected canards (Chinese Internet).歼20的尾部视图，锯齿状的轴对称喷口仿效了F35的设计，边条、全动尾翼和偏转鸭翼。

Aft view of F-22A Raptor displaying the rectangular TVC nozzles （Jeroen Oude Wolbers）
F22尾部视图的矩形矢量推力喷口。
Forward ventral view of J-20 prototype showing the flat lower fuselage, flat facet fuselage sides, and shallow join angle between the wings, canards and fuselage sides. Note the detail of the inlet geometry (Chinese Internet).歼20的前端腹鳍视图，平滑的机腹和机身两侧，机翼、鸭翼和机身两侧的下部以一定角度连接。请注意进气口的形状。
Near head on view of J-20 prototype showing the trapezoidal edge aligned inlet geometry , wing/fuselage join, and flat lower fuselage (Chinese Internet).歼20的前端近距离视图，进气口呈梯形对称分布，翼身融合，机腹平滑。

Rear quarter view of J-20 prototype showing the axi-symmetric nozzles and strakes (Chinese Internet).歼20的斜后视图，轴对称的喷口和边条。
-------------------------------------------------------------------------------Chinese Absorbent Materials Technology

中国的吸波材料技术
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The state of Chinese research in low observables absorbent materials technology is not well understood in Western nations, as there have been no substantial  official disclosures to date. The absence of disclosures, physical samples, or even viable imagery presents numerous challenges in determining what materials are intended for use in the J-20 design, or even what options are available to the Chengdu designers.中国在低可探测吸波材料技术上的研究，西方国家仍然一知半解，迄今为止仍然没有翔实的官方披露。由于缺少披露、材料样本和图片，这对判断歼20使用何种材料以及成都的设计者可能的选择都带来了极大的困难。
While official disclosures on production technologies are absent, these is a surprising number of recent unclassified basic research publications available, produced by Chinese researchers, dealing with the materials science of absorbers, especially Carbon Nano-Tube (CNT) absorbers, including absorbers loaded with conductive or magnetic materials. The number of papers and abstracts identified in this and related areas was of the order of thirty, mostly authored over the last several years, and published in English language journals and conferences. No attempt was made to survey Mandarin language publications.虽然官方没有披露生产技术，但最近发表的非机密的基础研究数量惊人，中国科学家在研究吸波材料技术，特别是碳纳米管（CNT）吸波材料，包括电磁吸波材料。相关领域论文和文摘的数量多达三成，多半在近些年被收录，并在英语期刊和学术会议上发表，从而不必去查阅汉语出版物。

注释：雷达吸波材料通常由两种或两种以上物质组成，按功能不同分为基体和填充剂。其中，填充剂决定了材料的吸波功能，基体则主要负载填充剂，并使材料具备一定的机械性能。填充剂会影响基体的机械性能，基体也会影响填充剂固有的电磁特性。
基体的电磁常数越小，对填充剂性能影响越少，所以通常用作基体的物质是有机高聚物和无机粘结剂。文中提到的基体主要是碳纳米管和环氧树脂。碳纳米管是一维纳米材料，具有高强度、高韧性、耐高温（已知材料中熔点最高的，3600℃以上）和良好的导电性。环氧树脂是分子结构中含有环氧基团的高分子化合物。由于分子结构中含有活泼的环氧基团，使它们可与多种类型的固化剂发生交联反应而形成不溶、不熔的具有三向网状结构的高聚物。
而填充剂主要分为两类，磁损性填充剂和电损性填充剂。常用的磁损性填充剂主要有铁氧体和金属粉末，其中，铁氧体是一种具有铁磁性的金属氧化物（比如四氧化三铁，俗称磁铁），具有高电阻、高介电性能和在高频时有着较高的磁导率等特点。常用的电损性填充料主要有炭黑和石墨。一旦雷达波进入吸波材料内，由于材料的导电率而引起能量损耗。
通常，电损性材料高频吸收效果好，磁损性材料低频吸收效果好。在实际应用中，把两者结合起来， 可以制得一种在较宽频率范围内吸收效果好的复合吸波材料。
Chinese research in RCS reduction is not confined to materials alone. A recent paper by Zhenghong and Mingliong details a derived Method of Moments algorithm for RCS computations. Work by Jiang et al details the use of genetic algorithms for the optimal design of complex multilayer absorber structures. Earlier research in conventional RCS modelling for design was produced by Cao et al.中国在RCS减缩方面的研究并不仅仅局限于材料。最近一份由郑宏和明龙（音译）发表的论文详细叙述了如何用矩量法来计算RCS。江等人利用遗传算法来进行多层复合吸波结构的优化设计工作。在此之前，曹等人就开始了传统的RCS建模设计的研究。
注释：矩量法（Moments Algorithm）是求解电磁场边界值问题的一种数值方法。主要是将积分方程化为差分方程，或将积分方程中积分化为有限求和，从而建立代数方程组 。遗传算法（Genetic Algorithm）是一种通过模拟自然进化过程搜索最优解的方法，由于遗传算法不依赖于梯度信息或其它辅助知识，只需要影响搜索方向的目标函数和相应的适应度函数，所以对于解决复杂的组合优化问题有着明显的效果。
Most of the materials research papers and abstracts surveyed were experimental, involving the fabrication and subsequent performance parameter testing of the fabricated material. The deeper theoretical analysis of loss mechanisms, and theoretical study of material behaviour in production applications, are uncommon in openly published work from China. This in many respects emulates the pattern observed in many Soviet unclassified basic research publications during the Cold War period.大多数材料研究论文和文摘，涉及制造和随后材料半成品性能参数的测试，都是试验性质的。中国公开发表了损耗机制的深层理论分析和应用产品材料特性的理论研究，这是十分罕见的，在很大层面上借鉴了冷战时期苏联非涉密基础研究的出版模式。
Annex B outlines the basic theoretical and practical concepts underpinning the design of absorbent materials.附录B列出了基础理论和吸波材料设计的实践思想。
Of specific interest in the context of Chinese stealth design is the respectable volume of  high quality academic research performed on CNT, ferrite loaded epoxy, or other materials for use as the absorbent or lossy component in epoxy or other polymer matrix absorbent or lossy coatings, laminates, panels or radar absorbent structures.倍受关注的中国隐形设计是建立在数量惊人的高质量学术研究之上的，包括碳纳米管、填充铁氧体的环氧树脂和其它吸波材料；环氧树脂损耗成分；其它高分子基质吸收剂；损耗涂层、层板、面板；雷达吸波结构。
注释：吸波材料按其成型工艺和承载能力，可分为涂敷型吸波材料和结构型吸波材料。一、涂敷型吸波材料又称吸波涂料，主要有铁氧体和金属超细粉末两种类型。铁氧体的优点是吸波性能好，便宜易得，缺点是比重太大；金属超细粉末的优点是重量轻，缺点是难以制造，价格昂贵。二、结构型吸波材料至少包括三层，其中最外层是透波层，如玻璃钢或芳纶纤维为基体的复合材料；中间层为电磁损耗层，由具有良好吸波特性的蜂窝结构或泡沫组成；最底层是反射层，必须具有反射雷达波的特性，一般采用强度刚度性能好的碳纤维复合材料制成。由于涂敷型吸波材料不参与结构承力，要付出额外的重量代价，而且还存在易脱落、侵蚀、工作不稳定的缺点，结构型吸波材料不存在上述问题，除此之外还有一定的透波性和吸波性，以及电磁特性的可设计性。
In CNT/epoxy materials a powder filler comprising CNT is loaded into an epoxy matrix, in a manner similar to traditional inclusion methods for powdered materials intended to alter the dielectric and magnetic properties of the resin. Epoxy resins in the microwave bands exhibit εr ~ 3.0 - 4.6 and δ ~ 0.01, making them a viable matrix for many applications, due to the toughness and durability of the material, and its relative ease of application.CNT/环氧树脂材料的填充粉末是由加载在环氧基上的CNT所组成，在某种意义上，这和利用粉状材料来改变树脂的电磁特性的传统内嵌工艺十分类似。在微波波段，环氧树脂的 εr（相对介电常数）大约是3.0到4.6，δ （介质损耗角）大约是0.01，这些可用基质能否应用于实际，取决于材料的韧性和强度，还有易用性。
注释：吸波材料的基本特性。一、匹配特性，电磁波入射到材料表面时，它能最大限度地进入材料的内部，而不是简单地被材料表面反射掉。二、损耗特性，进入材料内部的电磁波能迅速地几乎全部地衰减掉。调整吸波材料的介电常数和磁导率，可使材料的电磁特性既满足匹配特性，又满足衰减特性。
按吸波材料的吸收电磁波的方式，可分为谐振型吸波材料和吸收型吸波材料。一、谐振型吸波材料，从原理上讲，是靠回波之间的相互干涉作用来减弱回波强度。比如，在金属平板表面上涂上一层这种材料，除了一部分入射波直接反射外，其余部分透过涂层从平板反射，再穿过涂层形成另一部分回波。如果这两部分回波的振幅大致相等，相位相反，则发生相互干涉而被减弱。（也就是相消干涉）二、吸收型吸波材料，从原理上讲，是将入射波的电磁能量经在吸波材料中所产生的各种弱电和磁滞的损耗，转化为热量散失掉，从而减弱回波强度。第一种吸波材料与文中提到的相对介电常数εr和介质损耗角δ 有关。
Chinese research in CNT/epoxy absorbers seems to be mostly focussed on lossy dielectrics, rather than magnetically loaded materials intended as impedance matched coatings. Such materials are more useful as components in multilayered absorbent coatings or structures, rather than for applications such as control of specular skin reflections in aircraft, where exactly controlled impedance matching of the single layer coating strongly influences the performance of the coating.中国对CNT/环氧树脂吸波材料的研究似乎集中在损耗性电介质上，而不是把磁性材料作为匹配涂层的阻抗。这些材料应用在多层吸波涂料或结构上可以起到更显著的作用，而不是应用在诸如飞机表面镜面反射控制上，精确地控制单层涂层的阻抗匹配，可以影响涂层的性能。
There is no evidence in the open literature of a coordinated or focussed effort to develop thin lightweight impedance matched absorbent coatings for specular backscatter control in aircraft applications.在已公开的文献中，没有证据表明中国正在协调或集中研究既轻且薄的阻抗，使之可以应用在飞机镜面反射的吸波涂层上。
No effort was made to assess the performance of the surveyed materials as surface travelling wave absorbers. While numerical modelling of surface travelling wave absorption performance was feasible, without experimental data, calibration of any such simulation model was not possible.评估表明，把被研究材料作为表面行波吸收剂是不可行的。即便没有试验数据，表面行波吸收性能的数值也是可以模拟的，但是不能校准这些模拟数值。
As a result, most of the English language published Chinese materials research would yield products possibly suitable for other applications, but mostly not suitable for high performance coatings useful in aircraft microwave band specular RCS reduction.总而言之，大部分英文出版的中国材料研究出来的产品适用于其它应用，而不能用于飞机在微波波段的镜面RCS减缩的高性能涂料上。-------------------------------------------------------------------------------
Radar Cross Section Simulation Method / Simulator Design and CapabilitiesRCS的模拟方法/模拟设计和功能
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The Physical Optics (PO) method is used to predict the RCS of complex targets, in this instance the  Chengdu J-20 prototype. The three dimensional model for any such target comprises a collection of triangular facets, with shared edges.物理光学（PO）方法被用来预测复杂目标，也就是成都歼20原型机的RCS。这种目标的三维模型都是由很多共享棱边的三角切面组成的。

注释：物理光学（PO）法是采用stratton-chu（斯特拉顿-朱兰成）散射场的积分公式对复杂目标进行RCS的近似进算，但必须先满足三个条件。第一、高频条件，这样一来就保证了入射波波长远小于目标尺寸，那么就可以把入射波近似看作光线，认为目标上射线照不到的地方，其表面各点的场强为零。（也就是说在某一方向被遮挡住的机身其它部分的RCS贡献不参与计算）第二、远场近似，如果测量点到目标的距离要远大于目标尺寸，那么入射波可以看成是平面波。第三、切平面近似，假设目标表面上的任一点及其附近表面曲率半径比波长大得多，可以推导出一般目标散射场的物理光学法的计算公式。（下文会提到这三个条件，但语焉不详，看不懂没关系，复杂的公式就不罗列了，知道结论就行了）
The scattered field from each and every visible facet, for a given angle pair {θ, Φ} in elevation and azimuth, is computed using the far field radiation integrals.  It is assumed that the wavefront is planar and no parallax errors arise. The contributions from each of the facets are then summed to produce a total RCS for the angle pair {θ, Φ} in question. This method is a high frequency approximation that provides the best results for electrically large targets, and performs well in the specular direction假定波阵面是二维的，并且没有出现视差，对于一个给定的角度{θ, Φ} ，每个可见面的散射场都可以计算出它的远场辐射积分。每个面的贡献加起来就是{θ, Φ} 角度的总RCS。这种方法是高频的近似值，大型电子目标的最佳结果，并很好地演示了反射的方向。

注释：俯角是以铅垂线为基准，观察者的视线与铅垂线之间的夹角，用θ表示，范围是0°到180°。（当观察者在水平面以下的时候，也就是仰视，仍可以用大于90°的俯角来表示）方位角是二维平面中，从某点的指北方向线起，顺时针方向到目标方向线之间的水平夹角，用Φ表示，范围是0°到360°。俯角和方位角合起来构成一对视界角{θ, Φ}，决定了独一无二的三维视角。这个视角就是雷达波照射飞机的方向，上文提到过，入射波的方向也会影响RCS，下面的模拟会从不同的方向来测量飞机的RCS。
The simulation uses geometric self-shadowing of facet calculations, such that RCS contributions hidden by shadowing airframe features are removed. This mechanism does not implement diffraction effects at larger wavelengths.模拟器用来进行几何面的自投影计算，以致被屏蔽机身特性的RCS贡献被隐藏。这种机制不能实现更大波长的绕射效应。
The PO RCS simulation program implementation has manageable run–times because it requires minimum computer resources. It is implemented in C++ language to provide shorter computation times than earlier Physical Optics simulators, such as the NPS POFacets code, which is implemented in the interpreted Matlab language.出于对计算机资源占用最小化的考虑，物理光学RCS模拟程序的运行必须有可控的运行时间。C++语言比之前的物理光学模拟器运行更短的估算时间，例如 NPS POFacets（基于物理光学近似的面元法程序）代码，就是在Matlab语言下运行的。
At this time the simulator does not implement surface travelling wave modelling and associated edge or gap backscatter modelling, or edge diffraction scattering effect modelling. As the backscatter from these, in real aircraft, depends upon leading and trailing edge absorbent treatments, it is a reasonable assumption that in a production design these RCS contributions would be strongly suppressed as a result of effective treatments, and thus the magnitude of these RCS contributions would be smaller than specular returns, from angles other than the peak mainlobes.这次模拟器没有对表面行波、相邻边界和缝隙的反向散射，或者边缘绕射散射效应进行建模。由于这些反向散射取决于前后缘的吸收剂处理，因此在生产这些RCS贡献中采取合理的假设，将会强有力地抑制有效处理的结果，这些RCS的贡献将会比来自各个角度的量级要少的多，除了频域主瓣峰值的镜面回波。

注释：谈谈几种基本散射源。1、镜面反射，当电磁波照射到飞机的光滑表面时，反射光是平行的。镜面反射的回波的大部分能量集中在很窄的方向上，是一种很强的散射源，比如座舱罩、机翼和垂尾。2、边缘绕射，当电磁波入射到目标的边缘棱线时，镜面反射不复存在，散射波主要来自于目标边缘对入射波的绕射。边缘绕射是一种较强的散射源，比如平板或楔的边缘。3、爬行波绕射，电磁波照射到物体上，有一些入射线正好与物体表面相切，把物体分为照明区和阴影区。切于表面的入射线将沿阴影区表面一边“爬行”，一边向外辐射电磁波。比如电磁波侧向照射飞机，便会产生爬行波绕射现象。4、行波绕射，当电磁波沿细长物体头端方向附近入射时，在细长物体的表面不连续处（其数学模型二次不可导点）、不同介质交界处（如金属棒与塑料棒的连接处）以及细长体的端头处将产生绕射现象。（整个机身可以看做一个“细长体”，如果飞机的细长比越大，行波回波也就越大）5、尖顶绕射，当入射波入射到尖顶上，也会产生绕射现象。尖顶绕射是一种弱散射源，比如锥体的锥顶和飞机机头顶端。

The PO RCS simulator generates a raw data output as RCS magnitude values for a specified operating frequency, polarisation, and aspect angle pair {θ, Φ}, in ASCII text format.在指定了工作频率、极化方向和视界角 {θ, Φ}的情况下，物理光学RCS模拟器生成RCS幅度值作为原始数据以ASCII文本格式输出。
The integrity of the PO RCS simulation program was validated by modelling a range of basic shapes and materials coated panels, and comparing against published experimental third party results. The simulator generally displayed very low errors compared to published measurements, typically of the order of the error produced by digitising printed hard copy plots of experimental measurement results.物理光学RCS模拟程序要经过一系列的基本形状和涂层材料面板的建模，并且与第三方已发表的实验结果进行比对，才能验证其完整性。与已发布的测量值相比，模拟器拥有非常低的误差，特别是数字化印刷实验测量结果划分的硬拷贝时产生的误差。
Postprocessing tools were developed and employed to generate two different representations of the RCS data.后处理工具的开发和应用形成了两种不同的RCS数据表示法。
The first representation devised was labelled as the PolyChromatic Spherical Representation (PCSR), in which a translucent sphere is rendered around a two-dimensional rendering of the aircraft, where the surface of the sphere is divided into tiles by aspect angle pair {θ, Φ}. The colour of each tile represents the RCS from the angular direction determined by the path between the tile and the centroid of the aircraft. The colour encoding of RCS employs the same ordered colour sequence as is employed by US Government  and other agencies for weather radar rainfall density representation, as this is a well understood and intuitive encoding scheme.第一种表示法是用多色球面表示法来标记，让一个透明球体围绕飞机，然后把飞机的二维透视图投影到球面上，同时球面被视界角 {θ, Φ}划分成若干区块。每个区块的颜色都代表了由区块和飞机重心之间的路径所决定的角方向上的RCS。RCS的颜色编码采取的色序排序，与美国政府和其它气象雷达降雨强度发布部门使用的一样。

Example PolyChromatic Spherical Representation (PCSR) of J-20 specular RCS at 150 MHz. The dBSM value is represented by the colour scale at the bottom of the plot [Click to enlarge].150MHz下，歼20的镜面RCS多色球面表示法示例图。图片底部的色标就是dBSM值。
The second representation devised was labelled as the PolyChromatic Planar Representation (PCPR), in which a rectangular area is divided into tiles by aspect angle pair {θ, Φ}. The colour of each tile represents the RCS from the angular direction determined by the path between the tile and the centroid of the aircraft. The colour encoding of RCS employs the same ordered colour sequence as is employed in the PCSR scheme. All PCPR charts are further enhanced by the addition of rulers which separate the most critical azimuthal sectors, and elevation/depression angles第二种表示法是用多色平面表示法来标记，矩形平面被视界角 {θ, Φ}划分成若干区块。每个区块的颜色都代表了被区块和飞机重心之间的路径所决定的角方向上的RCS。RCS的颜色编码采取了与多色球面表示法相同的色序排序。所有PCPR图表都可以被添加的直尺所加强，区分最重要的方位面、仰角和俯角。

 
Example PolyChromatic Planar Representation (PCSR) of J-20 specular RCS at 150 MHz. The dBSM value is represented by the colour scale at the bottom of the plot. The rulers outline angular sectors of specific importance, from a survivability perspective.150MHz下，歼20的镜面RCS多色平面表示法示例图。图片底部的色标就是dBSM值。从存活能力来讲，直尺勾勒出的是比较重要的角度位面。

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Aircraft Model Features and Limitations飞机模型的特点和局限性

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The model used was an extant public domain 3,343 facet representation constructed from publicly available high and medium resolution photographic imagery of the J-20 prototype, observed in December, 2010, and January, 2011. 现阶段公共领域使用的模型，是根据2010年12月和2011年一月份对歼20原型机的观察，从公开拍摄到的中高分辨率的摄影照片进行构造的，一共有3343个面。
Two variants of the model were tested and one then employed. One model used axisymmetric exhaust nozzles fully open, and the other used axisymmetric exhaust nozzles fully closed. This was necessary to capture the specular returns from the nozzle exterior in the aft hemisphere of the aircraft, which vary strongly with nozzle position. As the nozzles open, the principal lobes of the specular returns rotate forward, and in the fully open position contribute mostly to the beam aspect RCS, where not shielded by the aft fuselage structure. Nozzle RCS from the forward and aft aspects varies weakly with nozzle position. Therefore all simulations presented are for a closed nozzle, which is the most frequent case in operational use of such aircraft, and thus of most interest. The nozzle rim includes serrations as observed on the prototype. The intent behind the use of serrations could be rim RCS reduction in the upper bands, but could also be to promote vortex generation and plume mixing to increase plume dissipation and thus reduce blackbody radiation from the plume in the near infrared bands.两种变体模型已经测试过了，并选择的其中的一种。一个模型的轴对称喷气口完全打开，其它模型的轴对称喷气口关闭。这对于捕捉喷口位置变化强烈的镜面回波十分必要。当喷口打开时，镜面回波的主瓣向前旋转，在完全打开的位置（不能被机尾结构阻挡）贡献了大部分侧向RCS。在喷口位置，前向和后向的RCS变化幅度很小。因此在所有仿真中，喷口都是封闭的，这是这种飞机最常见的，也是最感兴趣的模拟方法。原型机的喷口边缘有锯齿。锯齿的作用是在较高波段进行边缘RCS减缩，但也能促使涡流的形成和烟流的混合，从而增加烟流耗散，减少红外波段的黑体辐射。

注释：所谓黑体是物理学家为研究热辐射而定义的一种理想模型，在任何条件下，黑体对入射的电磁波完全吸收，而不会反射或投射。但根据热力学定律，凡事有温度的物体都会自行辐射电磁波，黑体也不例外，这就是文中提到的黑体辐射。这里的黑体应该是指机尾排气口喷出的气焰，虽说吸收了很多电磁波，由于自身温度的缘故也向外辐射电磁波，但这不属于雷达波隐身的范畴，而是红外隐身方面。所以文章说仿真模拟时要关闭尾喷口，就是为了避免红外辐射的干扰。
The primary nose mounted radar antenna radome is assumed to be a bandpass design, emulating United States fighter designs, and was assumed to be fully opaque at all frequencies of interest. The model assumes an insignificant structural mode RCS contribution from the radar antenna face and radar bay bulkhead, consistent with a properly designed bandpass radome in its stopband region. Given the absence of any useful data on the internal configuration of the radome and antenna bay, a more elaborate model would be speculative, unavoidably. Imagery of the prototypes does not show any evidence of the radome join to the fuselage, possibly reflecting the absence of a radome on airframes built to validate aerodynamics, shaping and flight systems. In a production design the radome seam / join to the fuselage can produce significant RCS contributions if poorly implemented.仿效美国战机的设计，机头的雷达天线罩假定为带通滤波设计，并对所有相关频率完全不透明。这个模型假定对结构模式的RCS贡献很少，包括雷达天线面和雷达舱壁，这与设计合理的带通滤波雷达罩在抑制频带方面保持一致。由于缺少天线罩和雷达舱内部配置的有关资料，不得已推测出来的模型可能会更精确。根据原型机的图片，没有证据显示天线罩嵌入机身，或许为了验证当机身上没有天线罩时，飞机的空气动力学、造型和飞行系统。如果做工不细，在生产设计中，天线罩焊接/嵌入机身可能产生重大的RCS贡献。

注释：带通滤波，只能通过特定频率的电磁波，对其余的波段则完全屏蔽，是为了使雷达天线罩可以发射和接受自身的雷达波，而屏蔽敌方的雷达波。
The engine inlet tunnels were modelled as Perfect Electrical Absorbers (PEA; Refer Annex E). Given the absence of any useful data on the internal configuration of the inlets and tunnels, a more elaborate model would again be entirely speculative. This is consistent with an ideal S-bend inlet tunnel clad with ideal RAM on its interior walls, and the use of an ideal engine face blocker. This is an optimistic assumption given historically observed difficulties in inlet tunnel signature reduction, as in many designs the inlet tunnel cavity RCS is a dominant wideband contributor in the forward aspect.发动机进气道的风洞被设计成完全电磁吸收。（PEA；参见附录E）由于缺少进气道和风洞内部配置的有关资料，推测出来的模型可能会更精确。这个模型拥有一个理想的S型进气道，理想的雷达吸波材料敷设在风洞外壁，并被用于发动机表面的预锻模。在许多设计中，进气道风洞凹腔在前向宽频带贡献了大量的RCS。而进气道风洞的信号减缩难以观察，所以这是一个乐观的假设。

注释：PEA，附录的解释为材料在自由空间的特性阻抗，对相关波长无限损耗（吸收）。
The exhaust tailpipe RCS contributions were also modelled as Perfect Electrical Absorbers (PEA). Given the absence of any useful data on the internal configuration of the tailpipes, a more elaborate model would be as before entirely speculative. The PEA model is consistent with an ideal  tailpipe internally clad with ideal heat resistant RAM, and the use of an ideal turbine face  and afterburner fuel spraybar blocker. This is an inherently optimistic assumption, as can be shown by employing an approximate model for an untreated tailpipe cavity, accounting for the reduction in projected nozzle area. This is detailed in Annex C.排气管的RCS贡献也被设计成了完全电磁吸收。由于缺少排气管内部构造的有关资料，推测出来的模型可能会更精确。这个模型是一个理想的排气管，理想的耐热雷达吸波材料敷设在排气管内部，并被用于理想的涡轮表面和再燃装置的燃料喷嘴架的预锻模。这是一个乐观的假定，因为采用未经处理的排气腔近似模型，喷口投影的面积将会减少。详见附录C。
The cockpit canopy transparency was modelled as a Perfect Electrical Conductor (PEC; Refer Annex E), to emulate the effect of a gold or other highly conductive plating layer in the polycarbonate laminate structure.透明的座舱盖被设计成全完导电体（PEC；参见附录E），来模拟黄金或其他高导电性的聚碳酸酯层状结构镀层。

注释：PEC，附录的解释为对所有相关波长而言，材料的特性阻抗为零，材料是一种理想化的导电金属。
The closed axisymmetric exhaust nozzle employs a stacked serrated trailing edge in the manner of the F-35 nozzle, reflecting photographic imagery of the prototype. As the structural shape of the gaps between nozzle petals is not known at this time, we modelled the open nozzle as simple cylinder.闭合的轴对称喷气口采用了F35喷口的堆叠式锯齿后缘，这是原型机的摄影图像。喷口菊蕊之间缝隙的结构形状还不清楚，我们把打开的喷口设计成了简单的圆柱体。
The photographic imagery of the J-20 prototypes was not of sufficient quality to incorporate any useful detail of panel join boundaries, door boundaries, and other surface features which produce RCS contributions due to surface travelling waves coupled to the aircraft skin. Even were such detail available, there is no guarantee production aircraft would retain the prototype configuration, reducing the value of any such results.歼20的摄影图像质量不高，没有充分地体现面板嵌入边界、门的边界和其它表面特征，它们产生表面行波与机身耦合的RCS贡献。即便有详细的资料，也不能保证成型机为了减少这些贡献而保持原型机的结构。
The position of the canards,  delta wing leading and trailing edge surfaces, and fully moving tail surfaces was set to neutral, reflecting an optimal cruise configuration at nominal supercruise altitudes and airspeeds. Large deflections by these control surfaces in flight would produce large but transient increases in specular backscatter.鸭翼的位置、三角翼前后缘的边缘曲面和全动尾翼表面被设定为中立，这是名义上的超音速高度的空速的最佳巡航构型。在飞行状态下，操纵面的大幅度偏斜将会产生巨大且短暂的反向散射增量。
The geometrical fidelity of the model was assessed by comparison with high resolution imagery released in January, 2011, specifically by comparing the shape of the model from the same aspect as the photograph. Particular attention was paid to the fidelity of angles, especially in the chines, engine inlet exterior, planform and wing/fuselage joins, as these determine the {θ, Φ} directions of the mainlobes and sidelobes in the specular returns.通过与2011年1月份泄露的高分辨率图像对比，特别是从相同的角度来比较模型和图像的外形来评估模型的几何精度。应当特别关注角度的精度，尤其是机脊、发动机进气口外部，俯视图和翼身融合，这些决定了镜面回波在 {θ, Φ} 方向的主瓣和副瓣。

注释：由于雷达波照射机身方向不同，RCS取值不同。本次模拟通过若干角度对歼20的RCS进行分析，球面投影图代表不同的视界角{θ, Φ}，上篇详细讲述过视界角，这里不再赘述。虽然每个球面图中飞机的位置不同，但在平面图中都是正视前向的，也就是说正中间的淡蓝色部分是机头方向，两边的蓝色是机尾，周围黄色和红色是两侧。不同的颜色代表不同的RCS值，并随着蓝、绿、黄、红而逐渐增大。

To establish the robustness of the 3D model for physical optics modelling, we explored the statistical distribution of edge lengths [x-axis] in the facet population [y-axis]. A substantial fraction of the facets are sufficiently large to yield good accuracy through most of the frequency bands being modelled for.要建立稳健的物理光学模型，我们就必须先弄清楚X轴上Y值的分布情况。绝大多数的Y值通过频段建模足以提供良好的精准度。

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What the Simulation Does Not Demonstrate
什么是非论证模拟

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1.The simulator at this time does not model backscatter from edge diffraction effects, although the resulting error will be mitigated by the reality that in a mature production design these RCS contributions are reduced by edge treatments;
1、模拟器不对边缘衍射效应的反向散射进行建模，尽管模拟结果的误差会比实际中低很多，但成熟的生产设计会通过边缘处理来减缩这些RCS贡献。
2.The simulator at this time does not model backscatter from surface travelling wave effects. In the forward and aft hemispheres these can be dominant scattering sources where specular contributions are low. The magnitude of these RCS contributions is reduced by edge treatments, lossy surface coatings, gap treatments, and panel serrations;

2、模拟器不对表面行波的反向散射进行建模。对于前后半球这些明显的散射源来说，镜面RCS贡献比较低。这些RCS贡献的量级可以通过边缘处理、损耗表面涂层、缝隙处理和面板锯齿来减缩。
3.The simulator at this time does not model backscatter from the AESA bay in the passband of a bandpass radome, due to the absence of any data on the intended design of same, the resulting error will be mitigated by the reality that in a mature production design much effort will be expended in suppressing passband RCS contributions;3、由于缺少同样的设计资料，模拟器不对有源相控阵雷达的带通滤波雷达罩的通频带反向散射进行建模。尽管模拟结果的误差会比实际中低很多，但成熟的生产设计会把注意力集中在抑制通频带RCS的贡献上。
4.The simulator at this time does not model backscatter from the engine inlet tunnels or engine exhaust tailpipes, due to the absence of any data on the intended design of same. In the forward and aft hemispheres these can be dominant scattering sources where specular contributions are low. The magnitude of these RCS contributions is reduced by suppressing these RCS contributions with absorbers, and in the case of inlet tunnels, by introducing a serpentine geometry to increase the number of bounces.4、由于缺少同样的设计资料，模拟器不对发动机进气口风洞或发动机排气管的反向散射进行建模。对于前后半球这些明显的散射源来说，镜面RCS贡献比较低。这些RCS贡献的量级可以通过吸波材料来减缩，进气道风洞则可以采用S型设计增加反弹次数。
5.The simulator at this time does not model structural mode RCS contributions from antenna and EO apertures, panel joins, panel and door gaps, fasteners and other minor contributors; although the resulting error will be mitigated by the reality that in a mature production design these RCS contributions are reduced by RCS reduction treatments.5、模拟器不对天线和光电孔径、面板连接、面板和门的缝隙、紧固件和其他元件的结构模式的RCS贡献进行建模；尽管模拟结果的误差会比实际中低很多，但成熟的生产设计会通过RCS减缩处理来降低这些RCS贡献。
6.The PO computational algorithm performs most accurately at broadside or near normal angles of incidence, with decreasing accuracy at increasingly shallow angles of incidence, reflecting the limitions of PO modelling. The simulator does not implement the Mitzner/Ufimtsev corrections for edge currents. While a number of test runs with basic shapes showed good agreement between the PO simulation and backscatter peaks in third party test sample measurements, even at incidence angles below 10°, characteristically PO will underestimate backscatter in nulls. This limitation must be considered when assessing results for the nose and tail aspects, where most specular RCS contributions arise at very shallow angles39.6、物理光学逻辑算法在舷侧和靠近入射角中间的位置计算较为精确，入射角度变小，精确度随之减少，这便是物理光学模型的局限。模拟器不会采用米茨纳/乌菲姆采夫的边缘电流修正法。在经过一系列的基本外形测试之后，物理光学仿真和反向散射的峰值与第三方实验数值高度一致，如果入射角低于10度，物理光学的反向散射趋近于零。对于机头和机尾而言，大部分的镜面RCS贡献出现在非常低的角度，所以其评估结果具有局限性。
7.The PO computational algorithm performs best where the product of wave number and dimension ka ≥ 5, where k ≈ 2πf [Table 5.1 in (1)], yielding errors much less than 1 dB. Knott cites good agreement for cylinders as small as 1.5 wavelengths in diameter1.7、物理光学逻辑算法在波数k≈2πf 、波数尺寸ka ≥ 5时计算结果最佳，产生的误差小于1分贝。诺特证明了圆柱体的直径为1时，与1.5倍波长相当。（这句话吃不准，实在理解不了是什么意思）
注释：ka是目标的电磁特征参数，a是目标的特征尺寸，随目标形状的不同取不同的参数。查阅了相关资料，这句话的意思是说，中低频区目标的散射场暂时没有有效的计算方式，只能采用高频区的方法来处理。波动理论尚不能计算柱体、锥体等简单形状的有限尺度目标的散射场精确解。

8.The simulator does not account for a number of environmental factors, such as air density profile at the aircraft skin boundary layer, thermal variations in absorbent material properties, and moisture precipitation. RCS contributions from these sources are negligible for the principal lobe magnitudes studied.8、模拟器没有计算一系列环境因素，比如飞机蒙皮边界层的空气密度、吸波材料性能的温度变化和湿度。它们的RCS贡献，相较于主瓣的研究量级，几乎可以忽略不计。
In practical terms, the combination of the J-20 aircraft geometry and the use of the PO method without the Mitzner/Ufimtsev edge current corrections will yield errors at the frequencies of interest of less than 1 dB for the beam aspect and tail aspect sectors, which both have dominant specular scatterers. The nose aspect angular sector results will underestimate RCS, in part due to the absence of shallow angle specular contributions not modelled by the Mitzner/Ufimtsev edge current corrections, and by the absence of surface travelling wave backscatter contributions from surface features, gaps and trailing edges.事实上，在侧向和尾部区域，如果相关频率低于1分贝，歼20的几何构成和没有采用米茨纳/乌菲姆采夫的边缘电流修正法的物理光学方法将会产生误差。机头部分的角度位面的RCS将被低估，在某种程度上取决于缺少低角度的非米茨纳/乌菲姆采夫边缘电流修正法的模型的镜面贡献，以及缺少表面特性、缝隙和机翼后缘的表面行波反向散射贡献。

注释：彼得·乌菲姆采夫，俄罗斯物理学家，1962年发布了名为《物理衍射理论中的边缘波行为》的论文，其中提到的有关从平面反射雷达波的理论被研制F117的美国工程师所采用。（米茨纳缺少相关资料）

In all instances, the errors arising from the limitations of the PO computation method all fall into areas where well established RCS reduction treatments using RAS, RAM or coatings would be used, thus reducing the relative magnitude of the errors in the resulting RCS result for angles other than the peak mainlobes produced by these backscatter sources.

在所有情形下，误差是由物理光学计算方法的局限性引起的，每个区域都使用吸波结构进行了RCS减缩处理，并使用了吸波材料或涂层，从而减少这些反向散射源产生的来自角度而非主瓣峰值的RCS误差的相对量级。
Importantly, even were the simulator capable of modelling shallow angle specular and non-specular RCS contributors, the PLA would not permit sufficiently detailed disclosures on the RCS reduction treatments applied to the airframe design, as a result of which reasonable assumed parameters would have to be applied instead of actual values.更为重要的是，模拟器拥有建模低角度镜面和非镜面RCS贡献的能力，解放军不会泄露过多适用于飞机设计关于RCS减缩处理的细节，因此合理假设的参数将会取代真实数值被应用。
The latter underscores the difficulty in attempting to perform highly accurate numerical RCS modelling of foreign airframe designs, where access to high fidelity shaping data, surface feature data, and materials type and application is actively denied.后者强调了试图建立外部机身设计的高精确数值RCS模型的困难，想要获取这些高精度的造型资料、表面特性资料、材料类型和应用是非常困难的。
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What the Simulation Does Demonstrate

什么是论证模拟

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1.The simulation can accurately capture the direction of mainlobes and sidelobes produced by specular backscatter returns, especially where major specular reflectors produce strong contributions; this includes broadside and lesser specular returns from the wings, control surfaces and major reflecting areas of the fuselage, inlet exteriors and nozzles;1、模拟器可以精确地捕获镜面反向散射回波的主瓣和副瓣的方向，尤其是主镜面反射器产生的大量贡献；包括来自舷侧、机翼、操纵面、机身的主反射区域、进气道外部和喷口的次要镜面回波。
2.For an untreated PEC skin, the simulation can accurately capture the absolute and relative magnitudes of mainlobes and sidelobes produced by specular backscatter returns, especially where major specular reflectors produce strong contributions; this includes broadside and lesser specular returns from the wings, control surfaces and major reflecting areas of the fuselage, inlet exteriors and nozzles;2、对于未经处理的完全导电体（PEC）表面，模拟器可以精确地捕获镜面反向散射回波的主副瓣的绝对量级与相对量级，尤其是主镜面反射器产生的大量贡献；包括来自舷侧、机翼、操纵面、机身的主反射区域、进气道外部和喷口的次要镜面回波。
3.In capturing mainlobes and sidelobes of major specular scatterers it permits an assessment of the angular extent in the nose and tail sectors where diffraction and surface travelling wave backscatter is dominant, and can still be suppressed effectively;3、为了捕获主要镜面散射的主瓣和副瓣，模拟器将会对机头和机尾的角范围进行评估和有效抑制，这些区域会产生很明显的衍射和表面行波反向散射。
4.Where a RAM surface treatment is applied in the model, it will present inferior RCS reduction performance to an actual treatment; so results produced will present a worst case performance result, to an order of magnitude.4、模型中应用了RAM表面处理的地方，其减缩性能相较于真正的处理会比较差；所以结果将会出现某一量级的性能非常糟的情况。
In summary, if the results of the Physical Optics specular return modelling yield RCS values from key aspects, at key frequencies, which are consistent with stated VLO performance values in US designs, to an order of magnitude, it is reasonable to conclude that a mature J-20 design will qualify as a genuine VLO design.总之，如果物理光学镜面回波在关键面和关键频率的建模结果和美国设计规定的VLO性能参数在同一量级保持一致，可以合理地推断出歼20的成熟设计备具真是VLO设计的标准。
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Specular Radar Cross Section Simulation Results

镜面RCS的模拟结果

-------------------------------------------------------------------------------Specular RCS was modelled for full spherical all-aspect coverage, for nine frequencies of interest. Frequencies were carefully chosen to match likely threat systems the J-20 would be intended to defeat in an operational environment. There are:对镜面RCS在9个频段上进行全方位立体式建模，这些频率都是经过挑选，用来匹配可能挫败飞行状态下的歼20的威胁系统，他们是：
1.150 MHz to defeat Russian built VHF band Counter-VLO radars such as the Nebo UE, Nebo SVU and Nebo M series, or the Rezonans N/NE series;
2.600 MHz to defeat UHF band radars such as those carried by the E-2C/D AEW&C system, or the widely used Russian Kasta 2/2E and P-15/19 Flat Face / Squat Eye series;3.1.2 GHz to defeat L-band surface based search, acquisition and GCI radars, and the Northrop-Grumman MESA AEW&C radar;
4.3.0 GHz to defeat widely used S-band acquisition radars, and the E-3 APY-1/APY-2 AWACS system;
5.6.0 GHz to defeat C-band Surface-Air-Missile engagement radars such as the MPQ-53/65 Patriot system;
6.8.0 GHz to defeat a range of X-band airborne fighter radars,  Surface-Air-Missile engagement radars such as the 30N6E Flap Lid / Tomb Stone, and 92N6E Grave Stone, and a range of Western and Russian Surface-Air-Missile seekers;
7.12.0 GHz to defeat a range of X-band airborne fighter radars,  Surface-Air-Missile engagement radars, and Surface-Air-Missile and Air-Air-Missile seekers;
8.16.0 GHz to defeat a range of Ku-band airborne fighter radars,  and Surface-Air-Missile engagement radars, and Surface-Air-Missile and Air-Air-Missile seekers;
9.28.0 GHz to defeat a range of K-band missile seekers,  and Surface-Air-Missile engagement radars;
1、150兆赫兹用来挫败俄罗斯建造的甚高频波段反VLO雷达，比如米波UE、米波SVU和米波M系列，或者Rezonans N/NE系列。
2、600兆赫兹用来挫败超高频波段雷达，比如被E-2/D（鹰眼）空中预警系统装载或者俄罗斯广泛使用的 Kasta 2/2E和P-15/19平面/矮小眼睛系列。
3、1.2千兆赫兹用来挫败L波段的搜索、捕获和地面指挥拦截雷达和诺斯罗普·格鲁门的梅萨空中预警雷达。
4、3.0千兆赫兹用来挫败广泛应用的S波段搜索雷达和E-3侦察机的机载空中警报控制系统。
5、6.0千兆赫兹用来挫败C波段地空导弹指引雷达，比如MPQ-53/65爱国者导弹系统。
6、8.0千兆赫兹用来挫败一系列X波段的机载作战雷达、地空导弹指引雷达，比如30N6E Flap Lid / Tomb Stone、92N6E Grave Stone和一系列西方和俄罗斯的地空导弹导引头。
7、12.0千兆赫兹用来挫败一些列X波段的机载战斗雷达、地空导弹指引雷达、地空导弹和空空导弹导引头。
8、16.0千兆赫兹用来挫败一系列Ku波段机载战斗雷达、地空导弹指引雷达、地空导弹和空空导弹导引头。
9、28.0千兆赫兹用来挫败一系列K波段导弹导引头和地空导弹指引雷达。
RCS simulation results are presented in PCSR and PCPR formats. The latter includes rulers to show the most important elevation/depression angle rings/zones, and the four azimuthal quadrants.RCS模拟结果采用多色球面表示法和多色平面表示法的格式。后者包括用直尺来标记最重要的俯仰角区域和四个方位象限。
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Analysis of Shape Related Specular Radar Cross Section

外形RCS的相关分析

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The results of the physical optics simulation modelling of specular RCS for the J-20 shape, using an idealised PEC skin for all external surfaces, are displayed in Tables 1 and 2, for a vertically polarised E component. An additional simulation was performed at 150 MHz, or a horizontally polarised E component, with results in Tables 1A and 2A.通过物理光学仿真模拟未经处理的PEC表面，在垂直极化的E方向得到的歼20外形镜面RCS的结果详见表1和表2。150兆赫兹或垂直极化的E方向进行的仿真是负价的，其结果在表1A和表2A。

Table 1. J-20 Specular RCS Model Results PEC [V-Pol]

Notation: The POFACETS simulator labels V-pol as “TM-z”, i.e. the magnetic H vector is transverse to the z-axis or vertical. This convention was retained for consistency in these simulation plots, with plots labelled TM being V-pol and plots labelled TE being H-pol.说明：POFacets模拟器的标记V-pol就是TM-z，也就是把磁力的H矢量转换到Z轴或垂面。这种约定在以下的模拟图中同样适用，平面图把TM标记成V-pol，把TE标记成H-pol。
注释：TE指水平极化波，入射波电场矢量E与入射面（入射波和法线组成的平面）垂直，入射波磁场矢量H与入射面平行。TM指垂直极化波，入射波磁场矢量H与入射面垂直，入射波电场矢量E与入射面平行。

Table 2. J-20 Specular RCS Model Results PEC [V-Pol]

150MHz

600MHz

1.2GHz

3.0GHz

6.0GHz

8.0GHz 

12.0GHz

16.0GHz

28.0GHz

 

Assumptions:A.Distant threats CRPL exponential refractive atmospheric model;
B.Near threats SBF refractive atmospheric model;
C.Spherical earth model;
D.Assumed aircraft altitude 36 kft;
E.For higher aircraft altitudes the depression angles increase for nearer threats.
假定：
1、远距离威胁CRPL（美国宇宙射线物理研究室）大气层模型折射指数；
2、近距离威胁SBF大气层模型折射；
3、球型地球模型；
4、假设飞机高度36千英尺；
5、飞机高度越高，俯角越大，近距离威胁也就越大。

Threat depression angles as a function of type and missile kinematic range, for various contemporary and legacy SAM systems of Russian/Soviet manufacture (C. Kopp).威胁俯角作为一个函数类型和导弹飞行范围，应用于俄罗斯/苏联制造的各种现代和传统的地对空导弹系统。（C·库珀）
Table 1A

. J-20 150 MHz Specular RCS Model Results PEC [H-Pol]

Table 2A. J-20 150 MHz Specular RCS Model Results PEC [H-Pol]

The starting point for any forensic analysis of the RCS of a new and hitherto unknown aircraft type is the study of the RCS of its shape, assuming a perfectly electrically conductive surface. This will permit identification of mainlobes and sidelobes, and their respective angular locations.分析任何一个新型和迄今未知的飞机类型的出发点都是假设一个完美的导电表面，研究其外形RCS。这样一来，可以判断主瓣和副瓣以及它们各自的角度位置。
As the simulation technique is confined to the Physical Optics method, care must be taken in the interpretation of results, as at grazing or shallow angles of incidence the method will usually underestimate the magnitude of the RCS. In the most critical nose and tail aspect angular sectors, a good design will have no major scattering sources producing specular returns captured by the simulation, and the RCS will be dominated by nonspecular mechanisms, primarily diffraction and surface travelling waves, engine inlet and exhaust backscatter, as well as the structural mode RCS of antennas, panel join gaps, or other electrical apertures.由于模拟技术局限于物理光学方法，对于较为平直和低入射角的结果解释必须谨慎，该方法通常会低估RCS的量级。在最重要的机头和机尾的角度位面，一个好的设计，其主反向散射源产生的镜面回波不会被模拟器捕获到，RCS也会被非镜面结构所控制，比如主要衍射和表面行波、发动机进气道和排气管，天线的结构模式RCS、面板连接缝隙或其它导电孔径。
Behaviour in the nose aspect angular sector, defined as ±45° in azimuth left and right of the nose, and between +5° in elevation, and -36° in depression, is generally very good across all bands simulated. No scattering sources producing significant specular RCS are observed at 3 GHz or any higher frequencies. The RCS performance will thus satisfy the Very Low Observable requirement that strong specular returns are absent. In this angular and frequency domain, the actual RCS performance of the design will be dominated by edge alignment to control diffracting edge mainlobe directions, and applied RAM and RAS. As the simulation cannot capture the behaviour of the inlet edges and tunnels, these peaks are absent.机头的角域通常定义为机头左右方位±45°和俯仰角的+5°到-36°之间，可以很好的穿过所有的模拟波段。非散射源产生的明显镜面RCS会被3GHz以上的频率观察到。强烈的镜面回波不复存在，隐身性能将会满足超低可探测性的条件。在这个角度和频域，边缘对齐控制着边缘衍射的主瓣方向，主瓣方向和应用的RAM/RAS决定了设计的真实隐身性能。模拟器不能捕获进气道口和风洞的性能，因为这些峰值并不存在。
At L-band and below, there is a pronounced increase in the calculated RCS within the nose aspect angular sector. This is a byproduct of the breakdown of the directional effect produced by smaller shaping features, which lose their ability to concentrate backscatter into narrow mainlobes. Indeed many physically smaller specular and diffractive regime optimised shaping features fall into the Raleigh scattering regime and lose effect wholly.在L及以下波段（频率越来越高），机头部分计算得出的RCS显著增加。这是由于较小的体积产生了方向分解，失去了把反向散射集中到狭窄的主瓣上的功能，从而衍生出的副产品。事实上，许多优化了造型特点、体积较小的镜面反射和衍射状态变成了瑞利散射状态，（译者注：瑞利散射是指半径比光的波长小很多的微粒对入射光的散射）完全失去了效果。
Behaviour in the tail aspect angular sector, defined as ±45° in azimuth left and right of the tail, and between +5° in elevation, and -36° in depression, is dominated by the scattering behaviour of the pair of axisymmetric nozzles, which has major specular, cavity and diffractive contributors, detailed in Annex C. The large diffraction backscatter from the nozzle rims below X-band is not captured in the Physical Optics simulation,  the tailpipe cavity backscatter is not represented, and the distinctive lobing structure of the nozzle petals above X-band is also not visible. 机尾的角域通常定义为机尾左右方位±45°和俯仰角+5°到-36°之间，其散射性能由一对轴对称喷口所决定，包括主要的镜面、凹腔和衍射贡献，详见附录C。在X波段以下，物理光学模拟器不能捕获到喷口边缘的大量衍射反向散射，排气口凹腔的反向散射也不存在，喷口边缘的天线扫掠结构在X波段以上同样难以发现。
There are two prominent mainlobes at ~±15° in azimuth left and right of the tail, centred at a depression angle of ~20° to ~40°, produced by the vertical tails which are not shadowed by a horizontal stabilator as would be employed in a conventional airframe design. While these produce strong specular returns, the depression angle through the centre of these mainlobes varies strongly with changing azimuth angle, and thus would present at any fixed depression angle only a narrow transient flash for a single azimuth.由于机身采用传统设计，垂尾没有被平尾遮挡住，在机尾左右方位±15°、俯角20°到40°之间产生了两个明显的主瓣。当它们产生强烈的镜面回波，随着方位角的变化，在通过主瓣中心时，俯角发生了强烈地改变，因此任何俯角只能固定一条狭窄的瞬间闪烁。
Behaviour in the left and right beam aspect angular sectors, defined as ±45° in azimuth left and right of the beam, and between +5° in elevation, and -36° in depression, is dominated by the scattering behaviour of the almost flat slab sides, canted vertical tail surfaces, strakes, and specular return from the nozzles. This could be described as classical “bowtie” lobing behaviour.左右两侧的角域通常定义为侧向的左右方位±45°和俯仰角+5°到-36°之间，其散射特性由大多数平滑截面、倾斜的垂尾表面、边条和喷口的镜面回波所决定的。据此，可以将其描述成经典的“蝶形”天线扫掠特性。
The specular return from the nozzles produces a pronounced mainlobe at 20° to 25° aft of the airframe beam, through most of the elevation band, with most of the mainlobe contained within a 10° degree width. There is a strong interference pattern discernable in the mainlobe, as the backscatter from the paired nozzles constructively and destructively interferes with changing aspect angle.来自喷口的镜面回波在机身两侧的尾部产生了一个明显的主瓣，在20°到25°区间穿过大部分高波段，并集中在10°宽度内。在主瓣上可以辨识出一个强烈的干涉图样，随着角度的变化，来自喷口的反向散射也在干涉加强和干涉相消之间变化。
The primary mainlobe produced by the slab fuselage sides is unusually wide in the azimuthal dimension at ~20° below the S-band as a result of the complex side curvature introduced by area ruling, for aerodynamic reasons. In the Ku-band the mainlobe separates into multiple closely spaced peaks, each associated with a particular extent of the fuselage side.机身两侧的截面产生的主瓣通常出现在方位角20°左右、S波段以下，由于空气动力学的原因，面积率决定了复杂边的曲率。在Ku波段，主瓣变成了多重密集峰值，每个都有一个与之有关的机身两侧的特别范围。
The extent to which the specular mainlobes in a ventral slab sided design, these including the J-20, T-50 PAK-FA, F-35 and F-22, should be made as narrow as possible, depends primarily on whether the aircraft is intended to penetrate an IADS deeply or not. The wider these lobes are, the greater the exposure time of the aircraft to a distant beam aspect threat, such as a missile battery. 包括歼20、T50、F35和F22在内的腹鳍板截面设计的镜面回波范围应该都会尽可能的窄，主要取决于飞机是否用于突破综合防空系统。波瓣越宽，飞机侧翼的远距离威胁也就越大，比如导弹连。
The overall conclusions which can be drawn from a forensic analysis of the shape of the J-20 prototype across the bands of interest are as follows:歼20原型机穿越相关频率，得出的外形分析总结如下：
1.The nose aspect sector has excellent potential for achieving Very Low Observable performance due to the absence of any major specular scatterers;1、机头部分没有任何主要的镜面反向散射，具有优秀的潜能达到VLO性能。
2.The tail aspect sector is largely degraded in RCS performance by the use of axi-symmetric nozzles which introduce strong specular and diffraction returns; the nozzles destroy the otherwise very reasonable behaviour of the rest of the airframe in this angular sector; the tail surface geometry introduces a further degradation in performance, but constrained to narrow lobes;2、机尾部分使用了轴对称喷口，产生强烈的镜面和衍射回波，大幅度削减了隐身性能；喷口摧毁了在这个角度位面机身其余部分非常良好的性能；尾翼面几何体的性能进一步弱化，但勉强能使波瓣变窄。
3.The beam aspect sector shows classical “bowtie” lobing behaviour, but the lobe widths are wider than otherwise necessary due to the use of smooth area ruling rather than discrete geometrically flat area segments.3、机身侧向呈经典的“蝶形”波数扫掠特性，但是波瓣比其它需要的更宽，这取决于使用的是平滑的面积率而不是离散的几何面。
If the production J-20 retains the axisymmetric nozzles and smoothly area ruled sides, the aircraft could at best deliver robust Very Low Observable performance in the nose aspect angular sector.如果歼20的生产保持轴对称喷口和符合面积率的平滑截面，飞机可以为机头方向提供强劲的隐身性能。
If the production J-20 introduces a rectangular faceted nozzle design, and refinements to fuselage side shaping, the design would present very good potential for  robust Very Low Observable performance in the S-band and above, in the nose and tail aspect angular sectors, and viable Low Observable performance above the S-band in the beam aspect angular sector.如果歼20的生产采用矩面喷口设计、改进机身侧面造型，强劲的超低可探测性能将会在S波段及以上范围展现出巨大的潜力，机头部分和尾部以及侧向在S波段及以上范围也会拥有良好的VLO性能。
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Analysis of Specular RCS with a Representative RAM Coating

敷设典型雷达吸波材料的隐身性能分析

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The results of the physical optics simulation modelling of specular RCS for the J-20 shape, using a RAM coating model for all external surfaces, are displayed in Tables 3 and 4. The RAM coating parameters are discussed below.在歼20外形的镜面RCS模型的所有外表面上敷设雷达吸波材料，物理光学仿真结果见表3和表4。接下来讨论RAM涂层的参数。
Modelling a RAM coated J-20 presents a number of interesting challenges, especially since so little is known about the materials available to Chengdu engineers, and the construction technique used on the airframe. It is not yet known with any confidence whether the J-20 is covered with metal alloy skin panels, carbon fibre composite skin panels, or some combination of the two. Moreover, if we consider the Russian Flanker as a case study, metal skin panels were progressively replaced with composite panels in later variants, so it is entirely conceivable that a metal skinned J-20 prototype could evolve over time into a composite skinned production vehicle.对敷设了RAM的歼20进行建模是一种很有趣的挑战，特别是在对成都的工程师们所使用的材料和机身的制造技术知之甚少的情形下。对歼20是否覆盖着金属合金蒙皮面板、碳纤维复合材料蒙皮面板或二者的合成物的秘密也不清楚。此外，如果我们把俄罗斯的苏27作为个案来研究，在之后的改进型号中，金属蒙皮面板逐渐被复合材料面板所代替，所以基本可以认定，随着时间的推移，金属蒙皮的歼20原型机可以改进成复合材料蒙皮的成品机。
Aircraft built for VLO will employ a range of specialised materials, applied to specific portions of the airframe to achieve very specific loss characteristics at specific frequencies. Unique materials would be employed to control specular returns, surface travelling wave returns, and edge returns, all from specific key aspects. 基于VLO建造的飞机将会采用一系列特殊材料，应用到机身的特殊部分，在特殊的频率上表现非常特殊的损耗特性。独特的材料将会被用来抑制来自所有重要位面的镜面反射、表面行波发射和边缘回波。
A Physical Optics simulator can model specular returns, but the simulator employed for this study does not at this time incorporate surface travelling wave effects, and edge diffraction effects. Therefore a materials model which addressed the latter two scattering mechanisms would only impact a specular RCS model through the behaviour of these otherwise optimised materials in a specular scattering regime at larger angles of incidence.物理光学模拟器可以对镜面回波进行建模，但是这次模拟不包括表面行波效应和边缘绕射效应。因此，用于后两种散射机制的材料模型，在镜面散射状态的入射角比较大的情况下，凭借其它优化材料的表现才能影响到镜面RCS模型。
At this time there are two well known strategies for the application of absorbers to aircraft.这时，对于飞机如何使用吸波材料有两种众所周知的方法。
The first strategy is to construct the aircraft with skin panels comprising different, structurally optimised materials, then coat the whole airframe with a highly conductive coating, such as a silver suspension in epoxy, and then robotically apply one or more coats of an epoxy or urethane matrix based RAM material. Weight will constraint coating thickness, for large areas, to as little as ~1 mm.第一种方法就是用不同的蒙皮面板建造飞机，再从结构上优化材料，然后用高导电涂层覆盖整个机身，比如银色的环氧树脂悬浮液，最后用机器敷设一层或几层以环氧树脂或尿烷为基体的RAM材料。重力将会把大面积的涂膜厚度控制在1毫米左右。
The advantage of this approach is simplicity, and considerable freedom in choices of skin materials, which are effectively hidden by the conductive substrate to the absorber. The disadvantage of this approach is that a very high performance absorber is required, which presents a range of challenges in achieving concurrently impedance matching to ~377 Ω, high permittivity and permeability, and low thickness and thus weight. 这种方法的优点就是简单易用，导电基质的吸收剂可以很好地隐藏蒙皮材料，这在蒙皮材料的选择上有着相当大的自由度。缺点是对吸收剂的性能要求很高，阻抗匹配必须达到377Ω左右，同时还要具有较高的介电常数和渗透性，以及较低的厚度和重量。
Corrosion and abrasion of coatings, resulting from handling damage, exposure to dust or sand particles, insects, rain droplets and hailstones at high velocities, and the permeability of coatings to water with concomitant electrolytic effects,  can increase operational and maintenance costs strongly through the resulting need for post flight inspections and coating repairs. Paint or surface treatment erosion or damage through these mechanisms is a well established problem in conventional aircraft where the surface material is primarily used for optical and infrared band camouflage and skin protection. Where the coating must meet a challenging broadband complex impedance specification, resilience to damage and erosion is a much more demanding design requirement.搬运损伤或者在非常高的速度下碰到灰尘或沙砾、昆虫、雨滴和冰雹，以及涂层与水发生电解效应，都会造成涂层的腐蚀和磨损，因此，对飞机进行检查和涂层维护同样会导致运行和维护成本的急剧增长。表面材料主要用于光学和红外波段的伪装以及蒙皮保护，通过刷漆和表面处理等机制来解决侵蚀和损害这类普通飞机上的既有问题。涂层必须要达到宽频复阻抗的要求，对破坏和侵蚀的回复能力的设计要求更高。
The second strategy is to construct the aircraft with composite skin panels either loaded with RAM, or laminated in production with a RAM sheet.第二种方法是使用混合了RAM的复合材料蒙皮面板或RAM片状生产的层板来建造飞机。
The advantage of this approach is that greater RAM depth can be achieved, and that the RAM is inherently more mechanically robust and durable compared to a coating, yielding lower operational and maintenance costs. The disadvantages of this approach are several. The RAM must provide some measure of impedance matching to a high permittivity and low impedance carbon-fibre or other composite skin; the airframe designers lose freedom in choosing skin panel materials for mechanical properties alone; and finally improvements in available RAM can only be accommodated by replacing most or all of the aircraft skin panels, rather than stripping and reapplying coatings during periodic depot maintenance cycles.这种方法的优点是可以达到更大的RAM厚度，与涂层相比，更为强韧和耐用，以及更低的运行和维护成本。缺点是RAM必须提供一些高介电常数的阻抗匹配和低阻抗的碳纤维或者其它复合材料蒙皮，机身设计者为了机械性能而牺牲了选择蒙皮面板材料的自由，（译者注：机械性能指材料的弹性、塑性、刚度和时效敏感性等）如果想要改进RAM的性能，就要更换大部分或全部的飞机蒙皮面板，而不是在定期维护中剥离和重新敷设涂层。
The second strategy is usually termed the “matched wave impedance” approach, which is typically employed when the substrate, such as an aircraft skin, is a non-conductive material such as a composite, with complex impedance properties. In this strategy, the coating applied over the skin is designed to have such dielectric and magnetic properties, such that the nett impedance of the coating and skin together approaches, ideally, free space at Z0 ≈ 377.第二种策略通常被称为“匹配波阻抗”方法，适用于飞机蒙皮是具有复阻抗性能而非导电复合材料的情况。这种方法，蒙皮应用涂层的设计是为了拥有电介质和磁性，这样一来，从理论上来说，在波阻抗（Z0）约等于377Ω时，涂层和蒙皮的纯阻抗接近自由空间。
注释：波阻抗就是入射电磁波的电场E和磁场H的绝对值之比，在自由空间里，波阻抗等于377Ω。自由空间相当于真空，不会对电磁波的各个参数产生影响。
The effectiveness of this strategy depends on finding a coating material with properties complementary to the substrate. It has the advantage of both layers attenuating the signal.这种方法的效果取决于找到一种补充基体性能的涂层材料。它的优点是双重信号减弱。
It is important to note that if an absorber presents a strong impedance mismatch to free space, the reflection from the mismatch will set an asymptotic bound on achievable RCS reduction of specular returns. Increasing material loss performance or thickness will not improve performance beyond this asymptotic bound.至关重要的是，如果吸波材料在自由空间出现强烈的阻抗失配，失配反射将会对可完成的镜面回波RCS减缩设置渐进限。增加材料的损耗性能或厚度不会使性能比这条渐进限更高。
No attempt was made to model treatments for surface travelling wave backscatter, as insufficient data was available on the geometry of panel and control surface boundaries, and as noted earlier, the choice of skin materials is unknown. The intent behind such treatments is to minimise the impedance mismatch at a panel boundary, or trailing edge, seen by a  surface travelling wave attached to the skin of the aircraft.不要试图对表面行波反向散射做模拟处理，因为没有足够关于面板和操纵面的几何资料可供使用，如前所述，蒙皮材料的选择是未知的。这种处理背后的意图是最大限度地降低面板边界或机翼后缘的阻抗失配，让附着于飞机蒙皮的表面行波可以看到。
Where dissimilar skin materials are employed without substantial absorbent coatings,  for instance, matching the impedance at the boundary between two panels of strongly differing impedance, would require a low impedance coating on the higher impedance panel, which would be far from the optimum required for broadside specular backscatter reduction. Treatment of trailing edges typically requires materials with high permeability, also suboptimal for specular backscatter reduction.采用不同的蒙皮材料，而不使用大量的吸波涂层，比如在两块完全不同阻抗的面板之间的边界上匹配阻抗，需要把低阻抗涂层敷设在高阻抗面板上，这样将会使远离舷侧的镜面反向散射减缩到所需要的最佳性能。
Stability of surface materials with changing temperature is a major consideration, given the wide operating temperature range experienced by supersonic gas turbine powered military aircraft. Stability with surface materials age is also important, especially for the second implementation strategy where an age related degradation in material performance incurs a very high cost in skin panel replacement. Neither of these considerations were addressed in this study.由于军用飞机是由超音速燃气涡轮驱动的，工作温度范围很大，随着温度的变化，表面材料的稳定性也是需要重点考虑的。表面材料的耐久度也很重要，尤其是第二种实施方法，材料性能的耐久度的下降会导致非常高的花费，用于更换蒙皮面板。这些注意事项都不在本次研究中得到解决。
The final choice in modelling the J-20 was to employ the second  implementation strategy where the aircraft is assumed to be constructed with composite skin panels either loaded with RAM, or laminated in production with a RAM sheet. The “matched wave impedance” approach was assumed, although none of the published Chinese materials possessed the required properties.对歼20建模的最终采用的是第二种实施办法，假定使用混合了RAM或RAM片状生产的层板的复合蒙皮面板来建造飞机。假设“匹配波阻抗”方法，尽管中国所公开的（吸波）材料并不具有所需属性。
This choice of using the second strategy was made as the intent of this study was to explore the long term potential for good Very Low Observable performance in the J-20 design. Composite skins with embedded absorbers provide greater RAM depth and thus better performance with a less mature RAM technology base. They are also less demanding in terms of handling in an operational environment, a major advantage for an operator reliant on less experienced conscript maintenance personnel.之所以选择第二种办法，是因为此次研究的目的是探究歼20设计是否具有出色的VLO性能的长期潜力。嵌入了吸收剂的复合蒙皮，其吸波材料层很厚，在还不成熟的RAM技术基础上有着较好的性能。他们同样对在工作环境的处理方面要求较低，操作员的主要优势是依赖经验不足的维修人员。
A question of interest which arose during this effort was that of which frequency bands the designers of the J-20 might optimise the design of a specular RAM coating for. Prima facie this may appear to be a simple question, but it is not.在这种努力下，出现了一个有趣的问题，歼20的设计者到底会为哪个频段去优化镜面RCS涂层。从表面上看，这似乎是一个简单的问题，但实际不是。
If we assume that combat attrition is a serious consideration in PLA-AF planning and design definition, then the two most obvious choices in optimisation are thus:如果我们假定战斗减员是解放军空军的规划设计之中着重考虑的，两个最佳的优化选择是：
1.L-band through S-band - most suited for a design intended to penetrate deep into an opposing IADS, the intent of the RAM being to defeat early warning and acquisition radars;1、从L波段到S波段，最适于突破敌方综合防空系统的设计，RAM存在的意图就是为了挫败预警和搜索雷达。
2.X-band through Ku-band - most suited for a design intended to fight inside its own supporting IADS, the intent of the RAM being to defeat X-band fighter radars, and Ku-band missile seekers.2、X波段到Ku波段，最适于在自己的综合防空系统支援下的战斗，RAM存在的意图就是为了挫败X波段的战斗雷达和Ku波段的导弹导引头。
Unfortunately, PLA-AF reasoning in this area is not well understood in the West, given the limited disclosures made to date. In turn, application of Western design priorities may not yield an accurate estimation of the PLA-AF's relative priorities in the design.遗憾的是，由于迄今为止有限的披露，解放军空军在这方面的解释西方并不十分了解。反过来，西方优先设计的应用并没有精确地估计到解放军空军相对优先的设计。（译者注：这句拗口的话意思是，西方以为制造出了以F22为首的一大批高精尖武器，这样一来就可以独领风骚了，却没有料想到TG优先发展国防尖端科技，在很短的时间里相继造出了歼10和歼20，让西方打错了如意算盘）
A complicating factor is uncertainty surrounding the choice of axi-symmetric exhaust nozzle geometry and ventral strakes in the long term. It is entirely conceivable that a mature production J-20 might employ a faceted rectangular nozzle in the manner of the F-22, and be completed without the strakes. Were the latter to prove true, the more likely RAM optimisation would be L-band through S-band, conversely, if the axi-symmetric exhaust nozzle is retained to production, then an X-band through Ku-band optimisation would be more likely.轴对称排气喷口的几何形状以及腹鳍边条周围环境的不确定性是一个复杂的因素。可以想象，成熟的歼20产品可能会采用F22式样的矩面喷口，完全不用边条。如果后者证明是正确的，最可能的RAM优化会是L波段到S波段，相反，如果生产中保留轴对称排气喷口，那么将会进行X波段到Ku波段的优化。
The final material combination employed was essentially “generic”, with an outer 2 mm epoxy layer loaded with a soft Ni-Zn ferrite (Configuration C, below), laminated with a 4 mm carbon fibre epoxy composite skin.最终采取的材料组合基本上是“通用的”，外面是一层2毫米厚的混合了软性镍-锌铁氧体的环氧树脂，被4毫米厚的碳纤维环氧树脂复合蒙皮覆盖。
Due to limited frequency coverage in data characterising the modelled RAM coating, simulations were performed only for six frequencies, from the L-band through to the Ku-band.由于资料中有限的频率覆盖，模拟只在从L波段到Ku波段6个频率下进行。

Some measure of the performance improvement achieved can be determined from the preceding chart, which shows specular RCS averaged across an angular extent in the beam aspect, across a range of frequencies. The beam aspect was chosen due to the dominant specular scatterers in this angular region. For a 2 mm ferrite loaded epoxy layer thickness laminated into a CFC panel, the absorber produces observable effect between S-band and Ku-band, improving with frequency. Best effect was achieved in the region of 12 GHz, of the order of 10 dB compared to PEC, all averaged across the same angular extent.上述图表中可以看到一些改进性能的措施，让镜面RCS均匀地穿过侧向的一个角度范围，穿过一系列频率。侧向取决于这个角度的主要镜面反向散射。2毫米的铁氧体-环氧树脂层压到氟氢碳（CFC）面板，在S波段和Ku波段可以看到显著的吸波效果，并随着频率的增加而提高。12兆赫兹区域的效果最好，与PEC相比大约10分贝，平均穿过相同的角度范围。
The variations in RCS behaviour observed with changing aspect reflect closely the behaviour observed with the PEC model simulation, detailed above. In particular, the RAM reduces the peak magnitude of and narrows the mainlobes in the specular return. This effect is most pronounced in the upper X-band and Ku-band, and weakest in the L-band.随着方向的变化，RCS行为的变化反映了PEC模型反震的行为，上文已作了详细的说明。特别地，RAM降低了峰值的大小，使镜面回波的主瓣变窄。这种效应在X波段和Ku波段以上最为明显，在L波段最弱。
In assessing what materials strategy to apply, several experimental simulations were performed to observe actual effectiveness, and the extent to which impedance mismatch impacted achievable RCS reduction.评估应用哪种材料策略，许多实验模拟都在观察真实效果和阻抗失配影响RCS减缩的程度。
The well characterised CNT/epoxy matrix RAM, by Zhang et al., was applied to a model of Zhang's test article used for measurement, and then as a 1 mm RAM coating over a PEC airframe skin, to establish whether this high permittivity material would be viable. The results reflected the strong impedance mismatch observed with the simulation of the initial test article, and this model was not pursued further. The material parameters are detailed in Table 5.张等人描述的性能出色的碳纳米管/环氧树脂RAM，也被张用作测量的实验模型，把1毫米厚的RAM涂层敷设在PEC机身蒙皮上，来确定高介电材料是否可行。结果表明，初次测验观测到了强烈的阻抗失配，这个模型不能追踪的更远。材料的参数详见表5。
The more refined ferrite loaded Fe-filled CNT/epoxy matrix RAM by Gui et al., was not well characterised, so the published performance curves were employed to reverse engineer the complex permeability and permittivity values, using an RCS simulation of the test article employed by Gui et al., and an iterated guessing algorithm. This material also provided very poor impedance matching, reflected in a reduced resolution simulation of the airframe with a 1 mm coating over PEC. It was also not pursued further.归（音译）等人精炼出的铁填充的铁氧体碳纳米管/环氧树脂RAM，（由于）没有详细的描述，所以使用RCS实验模拟装置和迭代的猜测算法，并采用公开的特性曲线来逆向推导复磁导率和介电常数。这种材料的阻抗匹配非常低，表现在缩减的1毫米涂层PCE的机身模拟分辨率。它也不能更进一步的追踪。

While the basic theoretical constraints for an impedance matched thin specular RAM coating predicted that neither material would be viable, it was nevertheless of interest to perform a quantitative simulation experiment to confirm this empirically.囿于基本理论所限，没有材料可以匹配很薄的镜面RCM涂层的阻抗，然而可以从经验上进行定量的仿真实验来确定。
A number of epoxy matrix coatings, using older and more recent ferrites, were also simulated, using a 4 mm thick carbon fibre epoxy composite substrate, emulating an aircraft skin.同样，也要模拟一些使用了较老的和较新的填充了铁氧体的环氧树脂涂层，使用4毫米厚的碳纤维环氧树脂复合基体来对飞机蒙皮进行建模。
The best specular RCS improvement observed involved the use of a theoretical impedance matched material, with real permeability and permittivity of ~15, and high loss tangents.观测到的最佳RCS性能涉及了理论阻抗匹配材料的使用，真实的磁导率和介电常数约等于15，这是一个高损耗因数。

Table 3. J-20 Specular RCS Model Results With RAM / CFC [V-Pol]

Table 4. J-20 Specular RCS Model Results With RAM / CFC [V-Pol]

1.2GHz

3.0GHz

  

6.0GHz

8.0GHz

12.0GHz

16.0GHz

Table 5. Representative RAM and Material Properties

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Conclusions

总结

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This study has explored the specular Radar Cross Section of the Chengdu J-20 prototype aircraft shaping design. Simulations using a Physical Optics simulation algorithm were performed for frequencies of 150 MHz, 600 MHz, 1.2 GHz, 3.0 GHz, 6.0 GHz, 8.0 GHz, 12.0 GHz, 16.0 GHz and 28 GHz without an absorbent coating, and for frequencies of 1.2 GHz, 3.0 GHz, 6.0 GHz, 8.0 GHz, 12.0 GHz, 16.0 GHz with an absorbent coating, covering all angular aspects of the airframe.本课题探讨了成都歼20原型机造型设计的镜面RCS。运用物理光学仿真算法在没有隐形涂层情况下分别进行了频率为150兆赫兹、600兆赫兹、1.2千兆赫兹、3.0千兆赫兹、6.0千兆赫兹、8.0千兆赫兹、12.0千兆赫兹、16.0千兆赫兹和28千兆赫兹的模拟，和在隐形涂层下150兆赫兹、600兆赫兹、1.2千兆赫兹、3.0千兆赫兹、6.0千兆赫兹、8.0千兆赫兹、12.0千兆赫兹、16.0千兆赫兹和28千兆赫兹的模拟，覆盖了整个机身的角度位面。
In addition, the performance of a range of Chinese developed radar absorbers was modelled, based on a reasonable survey of unclassified Chinese research publications in the area. None of the surveyed materials were found to be suitable for use as impedance matched specular radar absorbers.此外，中国研发的一系列雷达吸波材料的性能已经建模，基于一份非机密的中国该领域研究发行的调查报告。遴选的材料没有发现适用于匹配镜面雷达吸收剂的阻抗。
If the production J-20 retains the axisymmetric nozzles and smoothly area ruled sides, the aircraft could at best deliver robust Very Low Observable performance in the nose aspect angular sector.如果歼20的生产保留轴对称喷口和符合面积律的平滑截面，飞机最多只能为机头部分提供强劲的超低可探测性能。
If the production J-20 introduces a rectangular faceted nozzle design, and refinements to fuselage side shaping, the design would present very good potential for  robust Very Low Observable performance in the S-band and above, for the nose and tail aspect angular sectors, with good performance in the beam aspect angular sector.如果歼20的生产引进矩面喷口设计，改进侧面机身造型，强劲的超低可探测性能将会在S波段及以上范围展现出巨大的潜力，机头部分和机尾以及侧向也会有良好的性能。
In conclusion, this study has established through Physical Optics simulation across nine frequency bands, that no fundamental obstacles exist in the shaping design of the J-20 prototype, which would preclude its development into a genuine Very Low Observable design.总之，本课题是通过物理光学模拟穿越九个无线电波段，在歼20原型机的外形设计不存在根本缺陷的情况下，确保改进型达到真正的超低可探测设计。