超级军网澳洲军事专家库珀：歼20原型机隐身性能初步评估（下篇）
来源：百度文库 编辑：超级军网 时间：2024/05/06 18:27:07
译文来源:原文链接：http://www.ausairpower.net/APA-2011-03.html
http://www.ltaaa.com 译者：病中乃知
正文翻译:
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。
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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]
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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
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600MHz
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1.2GHz
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译文来源:原文链接：http://www.ausairpower.net/APA-2011-03.html
http://www.ltaaa.com 译者：病中乃知
正文翻译:
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。
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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]
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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
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600MHz
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1.2GHz
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http://www.ltaaa.com 译者：病中乃知
正文翻译:
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
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译文来源:原文链接：http://www.ausairpower.net/APA-2011-03.html
http://www.ltaaa.com 译者：病中乃知
正文翻译:
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
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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.
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.
12.0GHz
16.0GHz
-------------------------------------------------------------------------------
Conclusions
总结
-------------------------------------------------------------------------------
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。
http://www.ltaaa.com 译者：病中乃知
纯技术贴，版主 勿删
他们应该制作一个模型出来再分析
现在只能你猜我猜大家猜
太专业了看不懂NB啊
完全看不懂，机器翻译的吧
这个太有水准了……
这还真是个专家啊。
从龙腾网搬过来的吧
太专业了，看不懂啊
太专业了，看不懂啊
太长了，看不下去。
挑个Bug：前面有两个标题，翻成“非论证模拟”的，应该是“模拟没有描述什么？”的意思
太长了，看不下去。
挑个Bug：前面有两个标题，翻成“非论证模拟”的，应该是“模拟没有描述什么？”的意思
全是猜的，有本事自己到兔子家偷一架回去做真实测试！
嗯，大家都来猜猜看
人家是做分析
1.太专业
2.太长
2.太长
最后得看结论！ 那才是它想表达的！
说一千道一万，就是说两洞不咋地
大玩我猜我猜我猜猜
不过仅从照片就搞出来这么多话，也难怪TG对任何不准备广而告之的武器都保密的那么狠
换言之，J20已经相对成熟，咱不怕看
不过仅从照片就搞出来这么多话，也难怪TG对任何不准备广而告之的武器都保密的那么狠
换言之，J20已经相对成熟，咱不怕看
嗯，貌似澳大利亚没有造飞机的能力吧？那么澳大利亚专家从哪里获得这些数据的？不会是老美给的吧！
不能把主要的内容标红一下吗。
太难，先顶后看。
他怎么没和F-22的RCS对比一下，这样我这个门外汉也能看个大概～～～～～
过于专业，看不懂
讨论很详细，结论不明确
翻译成中文还是看不懂捏？
这种基于照片的建模不够精细，3000多个面对于这种分析来说太少太少了。不过，这个杂志还是很严谨的。比某些写手一句“鸭式布局不利于隐身”的结论，还是进步多了
不错 就是没看到结论
技术角度考虑问题。。。
实际上非专业人士有时候不需要搞这么复杂。。。
一个世界排名靠前的经济体，军事力量，政治力量。。
想要搞一款有突出目的性的工具，就必然要达到相当的技术水准，要不就根本没必要拿出来。。
实际上非专业人士有时候不需要搞这么复杂。。。
一个世界排名靠前的经济体，军事力量，政治力量。。
想要搞一款有突出目的性的工具，就必然要达到相当的技术水准，要不就根本没必要拿出来。。
虽然完全不懂是什么意思，但是看起来好像很厉害的样子
NND
从毕业就再没耐心看过paper的，签到， 后面保持队形。。。
从毕业就再没耐心看过paper的，签到， 后面保持队形。。。
就是机头部分的隐身很牛，但是尾部和侧面要想达到很好的的隐身性能就需要修形。
没耐心看完，只看结论，只是不知侧面稳身怎么不是很好？
好专业呀看来需要科普一下了！
和 大多数 预测 一致，菊花 破坏隐身匿踪。
一句也看不懂
这说的啥
江大爆料说是在0.1~0.3之间