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。
http://www.ltaaa.com  译者：病中乃知