2.5D Quantitative Millimeter Wave Imaging of a Hidden Object on a Simplified Human Body Model Using Value Picking Regularization

In this contribution, the authors provide a proof of principle for quantitative imaging of concealed objects on the human body using millimeter waves. A two-and-a-half-dimensional (2.5D) quantitative millimeter wave imaging algorithm is applied to reconstruct a hidden dielectric object on a clothed simplified human body model. At millimeter wave frequencies, the incident field is typically a fully three-dimensional (3D) Gaussian beam, illuminating only a limited spot on the body. Due to the large dimensions of the human body in terms of wavelengths, a 3D discretization is hardly feasible. Therefore, it is assumed that the electromagnetic properties of the body do not significantly change within the illuminated spot, along the longitudinal direction of a person. Hence, only the cross-section of a human body model is discretized. This 2.5D assumption however is still not sufficient to reduce the forward problem to a feasible size. Therefore, a priori knowledge on the illumination and on the scattering properties of the clothed human body is used to deduce a simplified model to describe the cross-section of the clothed human abdomen. The complex permittivity profile of a small dielectric object, hidden underneath clothing and representing some type of explosive, is reconstructed. The complex permittivity profiles of all other scatterers are assumed to be known. The presented quantitative inverse scattering algorithm is based on a Newton-type optimization, combined with an approximate line search and regularized by applying Stepwise Relaxed Value Picking regularization. The input data of the quantitative inverse scattering problem are synthetic scattering data since the authors are not aware of any amplitude and phase measurement data for concealed weapon detection yet made available to the inversion community at these high frequencies.     

被动毫米波成像系统设计

被动毫米波成像是公共安全检查工作的一个重要发展方向。目前,国内外 主要集中在对纯反射系统的面阵探测领域进行研究,其研发成本较高,而大口径离轴抛物面镜的 加工更是颇具难度。将几何光学和高斯波束相结合,基于毫米波透镜设计和研制了 一种适用于近场被动毫米波成像的准光学系统,其探测距离为1.5 m,成像面积为1.2 m×1.2 m, 空间分辨率优于3 cm。该系统可实现非接触式安全检查,因此在各种公共检查场所具有 广泛的应用前景。     

Two-dimensional scattering of a Gaussian beam by a periodic array of circular cylinders

The two-dimensional scattering of a Gaussian beam by a periodic array of circular cylinders is studied. The incident Gaussian beam is expressed as a superposition of plane waves of different amplitudes and different incident angles, using the plane-wave spectrum technique based on Fourier optics. For each plane wave, the scattered field is calculated with the T-matrix of an isolated circular cylinder and its lattice sums characterizing a periodic arrangement of the circular cylinders. The circular cylinders may be perfect conductors, dielectric or gyrotropic cylinders, as long as their T-matrices are known.     

A Comparison of Propagation Between Apertured Bessel and Gaussian beams

A true Bessel beam is a family of diffraction-free beams. Thus the most interesting and attractive characteristic of such beam is non-diffracting propagation. In optics, the comparisons of maximum propagation distance had been done between Bessel and Gaussian beams by Durnin and Sprangle, respectively. However, the results obtained by them are conflict due to the difference between their criteria. Because Bessel beams have many potential applications in millimeter wave bands, therefore, it is necessary and significant that the comparison is carried out at these bands. A new contrast criterion at millimeter wavelengths is proposed in our paper. Under this criterion, the numerical results are presented and a new conclusion is drawn.     

Backscattering enhancement of electromagnetic waves fromtwo-dimensional perfectly conducting random rough surfaces: a comparisonof Monte Carlo simulations with experimental data

Predictions of an exact numerical model for scattering from a surface randomly rough in two directions are compared with experimental data. The numerical model is based on Monte Carlo simulation using an iterative version of the method of moments known as the sparse-matrix flat-surface iterative approach (SMFSIA). Experimental data is obtained from millimeter wave laboratory experiments in which the bistatic scattering patterns of fabricated surfaces with known statistical parameters were measured. The surfaces studied have both a Gaussian height distribution and correlation function, so that their statistics are characterized by an RMS height and correlation length. An RMS height of 1 wavelength and correlation lengths ranging from 1.41-3 wavelengths are investigated, and the phenomenon of backscattering enhancement is observed both in the numerical predictions and experimental data. A comparison of the absolute value of the bistatic scattering coefficient as normalized by the incident power shows the theory and experiment to be in good agreement     

Pilot Contamination Suppression Based Coordination in Multi-cell Massive MIMO Systems

The conventional millimeter wave systems are mostly designed to operate only for the Gaussian noise model. In many physical channels, such as urban and indoor radio channels, the ambient noise is known through experimental measurements to be non-Gaussian. Hence, recent research findings state that a mixture noise model with additive impulsive noise is a more realistic approximation for millimeter wave channels. In this paper, we propose a novel approach to suppress the impulsive noise effects on single-user millimeter wave massive multiple-input-multiple-output system using an adaptive fuzzy logic filter. Hence, a fuzzy median filter is applied to the system and it is aimed to minimize the effects of the impulsive noise by ordering samples based on fuzzy rank. Simulation results show that the proposed filter successfully suppresses the impulsive noise effects and achieves a better bit error rate and spectral efficiency performance than the competing methods in the literature while also working efficiently in Gaussian noise.

     

高阶双曲余弦高斯光束的传输性质

引入了高阶双曲余弦高斯光束,结果表明这类光束在一定参数条件下呈现平顶光束特征。这类光束可用偏心高斯光束或双曲余弦高斯光束的相干叠加而得到,因而也是傍轴波动方程的解,并讨论了它们在一阶光学系统中的传播性质。     

基于贝塞尔波束的大景深毫米波介质透镜天线设计

提出了基于贝塞尔波束的大景深毫米波介质透镜天线的设计方法.利用轴锥镜生成贝塞尔波束,并根据成像要求分别设计了基于贝塞尔波束的毫米波介质透镜天线和基于高斯波束的毫米波介质透镜天线.在3mm波段进行了仿真测试及分析,仿真结果表明,所设计的基于贝塞尔波束的毫米波介质透镜天线的3dB宽度为3.23mm,景深约为228mm,相较于传统的基于高斯波束的毫米波介质透镜天线,基于贝塞尔波束的毫米波介质透镜天线可实现的景深提升至5倍以上.     

Transient scattering by resistive cylinders

The two-dimensional scattering of an electromagnetic pulse normally incident on a collection of infinitely long cylinders of arbitrary shape is considered. ForE-polarization an electric field integral equation is derived that is applicable to solid cylinders and/or thin sheets, resistive and/or perfectly conducting. The contribution of the self-cell at later times is carefully analyzed. The expression obtained represents a generalization of previously known results. For an incident Gaussian pulse, numerical results are presented for surface currents and far-fields, for perfectly conducting and resistive circular cylinders and strips. A fast Fourier transform (FFT) algorithm is implemented to obtain the backscattering radar cross section, which is in good agreement with results obtained from either exact continuous wave (CW) solutions or the method of moments.     

Analysis of Complex Dielectric Phase Gratings by Hybrid FEM-Gaussian Mode Expansion Technique

Hybrid technique of finite element method (FEM) and Gaussian mode expansion method is implemented for the analysis of transmission property of dielectric phase gratings used in holographic power combining systems. It takes advantages of the versatility of FEM and the simplicity of the mode expansion method. Apparently, this hybrid method is well suited for the analysis of phase gratings with complex profiles, which provide more degrees of structural freedom than those of classical rectangular groove gratings. The transmitted fields of an array of two and three fundamental Gaussian beams through the multi-stepped and curved gratings are calculated by the hybrid method. Numerical results show that much less phase distortion can be fulfilled for the reconstructed pseudo-plane wave by the modified phase gratings, especially the curved ones. This is advantageous for improving the combining efficiency in spatial millimeter wave and sub-millimeter wave power combining systems.     

Influence of Gaussian Beam on Terahertz Radar Cross Section of a Conducting Sphere

In RCS estimation, usually a plane wave is assumed; while in real measurements at terahertz frequencies, generally a Gaussian beam or a similar beam source is adopted. In this paper, the RCS of a conducting sphere is discussed under the condition that the incident wave is a Gaussian beam. In the estimation, the influence of 2.52 THz collimated laser beam on RCS is discussed and the RCS changing with scattering angle and some other factors is obtained; at the same time, the comparisons between different incident beams, plane wave and Gaussian beam, are also given. The estimation results show that choosing a beam width of 40 mm is appropriate when the sphere radius is 10 mm and the distance between the sphere and the beam source is 1 m.     

An analysis of small aperture multimode horn as quasi-optical Gaussian beam radiator

In this paper a small aperture multimode horn is analysed by full-wave method and the coupling efficiency to Gaussian fundamental mode is calculated. The coupling efficiency of exceeding 0.98 is obtained over 4 GHz bandwidth. This horn may be used to connect waveguide with quasi-optical element in millimeter wave system and also may be used as an element in imaging array.     

基于频率选择表面的毫米波压缩感知成像

基于频率选择表面,提出了一种毫米波压缩感知成像方法。通过在频率选择表面单元中加载开关二极管,并随机控制它们处于开/关状态,设计了一种可随机切换的新型毫米波成像掩膜板。通过将这种随机掩膜板放置于毫米波天线上,能够构造出相应的随机测量矩阵并获取足够多的有效测量次数。利用恢复重构算法进行了成像仿真验证,结果证实了所提方法的可行性。     

涡旋光束经过散射介质产生散斑的理论和实验研究

研究了涡旋光束经过散射介质后形成的散斑特性 ．运用概率统计理论和光束传输理论,模 拟了不同拓扑电荷数的涡旋光束经过散射介质后形成的散斑,以及散射介质颗粒尺度对散斑 特性的影响。模拟结 果表明,随着涡旋光束拓扑电荷数的增大和散射介质颗粒尺度减小,形成 的散斑颗粒尺寸逐渐减小。实验上,利用螺旋相位板(SPP)产生涡旋光束,使其透过散射介 质后形成散斑。实验结果 表明,涡旋光束经过散射介质后,随着散射介质颗粒尺度减小,形成的散斑对比度逐渐增大 ;随着涡旋光束拓 扑电荷数的增大或散射介质颗粒的减小,所形成散斑的尺寸减小。实验结果与模拟结果 相吻合。     

基于物理光学法的近场多入多出雷达成像模拟

针对点目标扩展函数(PSF)不能有效分析复杂目标在毫米波近场多入多出(MIMO)雷达成像中的散射机理问题，研究了一种基于近场物理光学散射计算数据的毫米波MIMO雷达成像模拟方法。该方法利用近场物理光学方法，获得包含阵列构型和目标散射信息的近场计算数据，并通过近场MIMO成像处理器实现近场MIMO成像的全过程模拟。利用D波段“T”字型二维稀疏MIMO阵对复杂的三维目标开展了近场成像实验，仿真和实验结果表明，模拟结果与实际成像结果有很好的一致性。该方法能够分析近场MIMO成像系统的成像性能，为近场MIMO成像的阵型设计提供支撑，揭示复杂目标的近场散射特性与成像机理。     

5G毫米波QuaDRiGa平台信道仿真与验证研究

第五代（5th-Generation,5G）移动通信对毫米波信道模型提出了更高的要求,如支持三维（three-Dimensional,3D）多入多出（Multiple-Input Multiple-Output,MIMO）、有良好的空时连续性和时间演进特性及毫米波段仿真能力等.第三代合作伙伴计划（3rd Generation Partnership Project,3GPP）,推荐准确定性无线信道产生器（Quasi-Deterministic Radio Channel Generator,QuaDRiGa）为5G首选仿真平台,但目前尚无开展QuaDRiGa仿真平台在毫米波段的仿真验证成果.本文基于26 GHz的毫米波段室外微蜂窝场景下的视距与非视距实测数据,在大尺度信道参数统计和时间演进特性两方面开展了对QuaDRiGa平台的仿真验证.结果表明,QuaDRiGa仿真结果与实测数据能够很好地吻合,验证了QuaDRiGa仿真模型在毫米波段的适用性.     

Planar Log-Periodic Antennas on Extended Hemishperical Silicon Lenses for Millimeter/Submillimeter Wave Detection Applications

In this paper, the radiation properties of log-periodic (LP) antennas on extended hemispherical dielectric lenses are investigated. The starting point is the far field pattern for the log-periodic antenna on a semi-infinite silicon substrate obtained from numerical simulation. Then the effects of extended hemispherical silicon dielectric lenses on this far field pattern are evaluated using ray tracing and field integration techniques. The far fields patterns out of the lenses are derived as a function of the extension length (L), from which the optimum L can be determined. The coupling efficiencies of the pattern to Gaussian beams are also calculated. The computation results show that the log-periodic antennas have good performance in terms of impedance and pattern and can be used in many submillimeter/THz systems. The simulation methods are verified by comparing the simulation results with experimental data from literature. The utilized approach represents an effective method for log periodic antenna-lens system design at millimeter/submillimeter wavelengths.     

厄米-高斯波束对各向异性圆柱的散射特性研究

为了研究厄米-高斯波束在各向异性媒质中的散射特性，采用了将各向异性圆柱的散射场和内部场用圆柱矢量波函数展开，应用电磁场边界条件和投影法，提出了一种分析单轴各向异性圆柱对厄米-高斯波束散射特性研究的精确半解析方法; 获得了厄米-高斯波束通过单轴各向异性圆柱的内场以及近场的归一化强度分布图; 对两种不同的厄米高斯波束入射情形做出了分析和对比。结果表明，两种波束在通过圆柱后都有入射波和反射波叠加而成的驻波现象，而TEM₁₀(x′)模式厄米-高斯波束入射后近场强度增强，且有明显的折射现象。该研究结果对厄米-高斯波束的应用具有一定的参考价值。     

MIMO雷达三维干涉诊断成像方法

2维合成孔径雷达(Synthetic Aperture Radar, SAR)和逆合成孔径雷达(Inverse Synthetic Aperture Radar, ISAR)成像是目标散射机理高分辨率分析和散射诊断测量的重要手段,现有被广泛采用的技术主要包括转台ISAR和导轨SAR成像技术。相比于传统的2维成像,3维成像可以提供目标局部散射中心在空间的3维位置和散射强度信息。因此,探索新的、可工程化实现与应用的目标3维成像技术是一项极具吸引力的工作。该文提出一种基于多输入多输出(Multiple-Input Multiple-Output, MIMO)阵列技术的3维干涉成像方法。首先,设计并试验了一种具有高孔径利用率和通过虚拟孔径实现干涉成像功能的MIMO阵列;其次,分析了MIMO阵列合成的两组虚拟孔径所成两幅2维雷达像的干涉相位与目标散射中心高度之间的关系,发展了MIMO雷达3维干涉成像算法;最后,通过数值仿真和原理样机实验验证了所提方法在目标散射机理分析和诊断测量应用中的可行性和有效性。      

Multiple Scattering Solution of Millimeter Wave Propagation in Strong Sandstorm

As the operating frequencies of communication systems more higher into the millimeter wave range, and the density of particles in medium is more denser, the effects of multiple scattering in sandstorm become more significant. This paper treats the problems of electromagnetic multiple scattering in strong sandstorm by the Monte Carlo method. Based on the analytical theory of multiple scattering, the millimeter wave propagation and scattering in discrete random media are investigated by means of the particle-tracking technique. The millimeter wave is regarded as a Markov chain of wave particle collisions in a medium in which it is scattered and absorbed. Considering the effect of multiple scattering, millimeter wave attenuation induced by strong sandstorm is simulated numerically. The values of theoretical calculation are in good agreement with the measured results of simulated experiment at 34 and 93 GHz.