Overview of an image-based technique for predicting far-field radar cross section from near-field measurements

For the last 18 years, our group has been developing a variety of near-field-to-far-field transformations (NFFFTs) for predicting the far-field (FF) RCS of targets from monostatic near-field (NF) measurements. The most practical and mature of these is based on the reflectivity approximation, commonly used in ISAR imaging to model the target scattering. This image-based NFFFT is also the most computationally efficient because - despite its theoretical underpinnings - it does not explicitly require image formation as part of its implementation. This paper presents a formulation and implementation of the image-based NFFFT that is applicable to two-dimensional (2D) spherical and one-dimensional (1D) circular near-field measurement geometries, along with numerical and experimental examples of its performance. We show that the algorithm's far-field RCS pattern-prediction performance is quite good for a variety of frequencies, near-field measurement distances, and target geometries. In addition, we show that the predicted RCS statistics remain quite accurate under conditions where the predicted far-field patterns have significantly degraded due to multiple interactions and other effect.     

Radar cross section of curved plates using geometrical and physical diffraction techniques

Geometrical and physical optics techniques, supplemented by their respective extensions, i.e., geometrical and physical diffraction, are applied to the problem of finite cylindrically curved plates. Numerical calculations of the radar backscattering cross sections were made, and a graphical comparison of these methods with experimental results is made. Keller's and Ufimtsev's theories axe discussed and compared as they apply to this problem.     

Radar cross section of insects

X-band measurements of radar cross section as a function of the angle between insect body axis and the plane of polarization are presented. A finding of particular interest is that in larger insects, maximum cross section occurs when the E-vector is perpendicular to the body axis. A new range of measurements on small insects (aphids and planthoppers) is also described, and a comprehensive summary of insect cross-section data at X-band is given.     

Radar cross section map for straight wire

Radar cross section (RCS) patterns of a thin straight wire have been computed, and the results have been plotted as constant RCS contours on the frequency-aspect plane for a twenty-to-one frequency range. The resulting map illustrates how the resonant peaks and interference nulls vary simultaneously with frequency and aspect, providing a clear picture of the backscattering behavior and allowing reasonable extrapolation to frequencies considerably higher than those actually calculated.     

双反射面天线的雷达散射截面

近年来,降低天线的雷达散射截面已是电子对抗领域中的重要课题。该文针对已广泛应用的双反射面天线讨论降低其雷达散射截面的方法。结果表明,在保持增益不变的情况下合理选择主反射面的焦距是能够达到降低雷达散射截面的需要的。     

Radar cross section of long wires

Using a continuous wave (CW) Doppler radar at 60 GHz, the radar cross sections of long metallic rods were measured. The results show linear increase with growing distance between radar and rods. A new expression for the radar cross section, which was also derived, demonstrates good agreement with the measured data.     

Radar cross section of axisymmetric objects

A method for computing the resonant region scattering by slender axisymmetric objects with arbitrary surface impedance is outlined. This method employs matching of the electric and magnetic fields on axis. Results obtained by this method have been used to generate contour maps of radar cross section (RCS) as a function of frequency and aspect. Maps for three conducting cones and a cone-spheroid covering the diameter-to-wavelength range of 0.05 to 0.70 are shown. The relationship of the high and low frequency asymptotic behavior to the mapped results is discussed. Computed and measured RCS patterns are compared.     

Radar cross section of complex targets

A summary of the development and verifications of a computer code, RECOTA (return from complex target), developed at Boeing Aerospace for calculating the radar cross section of complex targets is presented. The code utilizes a computer-aided design package for modeling target geometry in terms of facets and wedges. It is based on physical optics, physical theory of diffraction, ray tracing, and semiempirical formulations, and it accounts for shadowing, multiple scattering and discontinuities for monostatic calculations     

Radar cross section of a long wire

Monostatic radar cross-section (RCS) results for five- and eleven-wavelength straight wires are presented. The numerical RCS values which are obtained from solving Pocklington's integral equation for the induced current by collocation fall within 1 dB of the experimental measurements over all major lobes of the RCS pattern. The computer times required for the computations are 1.2 and 7.6 seconds for the five- and eleven-wavelength cases, respectively.     

The bi-polar planar near-field measurement technique, part II:near-field to far-field transformation and holographic imaging methods

A novel customized bi-polar planar near-field measurement technique is presented in a two-part paper. This bipolar technique offers a large scan plane size with minimal “real-estate” requirements and a simple mechanical implementation, requiring only rotational motions, resulting in a highly accurate and cost-effective antenna measurement and diagnostic system. Part I of this two-part paper introduced the bi-polar planar near-field measurement concept, discussed the implementation of this technique at the University of California, Los Angeles (UCLA), and provided a comparative survey of measured results. This paper examines the data processing algorithms that have been developed and customized to exploit the unique features of the bi-polar planar near-field measurement technique. Near-field to far-field transformation algorithms investigated include both interpolatory and non-interpolatory algorithms due to the a typical arrangement of the bi-polar near-field samples. The algorithms which have been tailored for the bi-polar configuration include the optimal sampling interpolation (OSI)/fast Fourier transform (FFT), Jacobi-Bessel transform, and Fourier-Bessel transform. Additionally, holographic imaging for determination of antenna aperture fields has been incorporated to facilitate antenna diagnostics. Results for a simulated measurement of an array of infinitesimal dipoles and a measured waveguide-fed slot array antenna are included. Appropriate guidelines with respect to the advantages and disadvantages of the various processing algorithms are provided     

水下近场探测与成像的光学调制技术研究

基于光学调制的水下探测与成像技术是目前最先进的水下光电探测技术之一。本文结合国外最新的理论研究成果、实验装置与实验结果对水下近场探测与成像的光学调制技术进行了进一步的探索。论证了光学调制技术作为水下探测方面的最新技术,其相对于众多成熟技术的优势与在该领域的发展潜力,并对水下环境特征、基于频域的水下探测技术以及应用于水下近场成像的时变强度调制技术进行了分析与讨论。     

Fast algorithm for calculation of radiation integral and its application to plane-polar near-field/far-field transformation

An efficient algorithm for calculation of the radiation integral is described. The process is presented in the form of a crosscorrelation which is carried out by utilising the fast Fourier transform. Applications to a plane-polar geometry and to the reflector antenna are considered and the results of simulations are presented as validation of the process.     

太赫兹近场合成孔径成像与焦平面成像对比

针对近场目标高分辨力成像,基于220~325 GHz频段的近场雷达收发模块,在相同测量条件下,分别采用合成孔径雷达成像以及焦平面成像。对比合成孔径成像算法以及焦平面测量法的优劣,获得详细的测量参数以及成像效果对比,用于太赫兹近场成像分辨力的提高。     

微球透镜近场聚焦及远场成像仿真研究进展

微球超分辨显微成像技术能够突破衍射极限并成倍提高传统光学显微镜的成像分辨率。因其具有成像系统简单,可实时成像,无需荧光染料标记,能在白光照明条件下工作,且可与市场上成熟的显微镜产品相兼容等优点,具有重要研究价值与广阔应用前景,发展潜力巨大。该技术发展至今已取得了众多令人瞩目的研究成果,但现阶段的研究主要集中在微球超分辨成像规律、成像质量的提高、微球的操控方法上。而针对微球透镜的超分辨成像机理与模型,目前尚未形成完善统一的认知与可靠一致的解释。在此背景下,文中梳理归纳了微球透镜近场聚焦及远场成像机理、数学模型、仿真技术等方面的研究工作,分析现有工作的意义与所存在的不足,指出该领域需要着重解决的问题,并对微球成像技术未来的发展方向给予展望。     

Radar cross section of arbitrarily shaped bodies of revolution

The radar cross section (RCS) of an arbitrarily shaped, homogeneous dielectric body of revolution (BOR) is evaluated by the surface integral equation (SIE) formulation and the method of moments. Method accuracy is verified by the good agreement with the exact solutions for the RCS of a dielectric sphere. To demonstrate the advantages of this method, the RCS for a complex BOR model of human torso is computed with a nonaxially incident plane wave. Seven Fourier modes are considered in the computation. The SIE and approximate integral equation (AIE) formulations are next given for the RCS evaluation of a composite dielectric and conducting BOR. For the cases considered, both formulations give the same surface currents and RCS results. However, significant savings in computer storage and CPU time are realized for the AIE approach, since only one current (electric or magnetic) need be determined for RCS evaluation     

Radar cross section of a small low-pitch angle helix

A method of calculating the radar cross section of a dipole deformed into a helix of low-pitch angle is briefly discussed. Theoretical backscatter results are presented that show how the cross section varies as the helix coils into several turns. An interesting property of the current distribution is also discussed.