Polarization isolation requirements for linear dual-polarization weather Radar in simultaneous transmission mode of operation

A dual-polarization radar system operating in simultaneous transmission mode of both horizontal and vertical polarization states is a viable implementation if only copolar measurements are needed. The simultaneous transmission of horizontal and vertical polarizations results in an arbitrary elliptical polarization state transmitted, whereas the reception states in horizontal and vertical polarizations are neither copolar nor cross-polar to the transmitted state. Because of this, it is often referred as the hybrid mode. Previous studies have shown that the hybrid mode in the linear horizontal and vertical polarization basis is capable of providing measurements similar to the alternate transmission mode for most measurement conditions. These findings are based on the assumption of perfect sensing systems. This paper presents the results of radar system limitations on hybrid mode measurements that in turn are converted to system requirements. It is shown that the polarization purity requirement is more stringent for the hybrid mode compared to the alternate mode of operation.     

有限元法结合周期边界条件分析介质光栅衍射

应用周期边界条件建立了分析介质周期结构散射问题的有限元格式。求解域仅为周期结构的一个栅单元尺寸。分析计算了位相型透射光栅的衍射效率,栅单元结构分别为矩形和直角三角形。由于有限元方法的离散网格可以很好地匹配介质边界,该方法可以分析任意栅单元截面形状的介质栅形结构。     

Wave Polarization Effects on the Transmission and Reception of lonospheric Radio Waves

The effects of wave polarization on the transmission and reception of ionospheric radio waves have been discussed. Special attention was given to the effects of polarization on the excitation of characteristic waves in the ionosphere, on the absorption losses in the ionosphere, on the reception of arbitrarily polarized plane waves, and on the polarization coupling losses. In this work only one-hop paths were considered and it was assumed that the operating frequency is in the HF region so that ray theory treatment may be applied with high accuracy. The results of investigation have shown that wave polarization is an important and sometimes critical factor in the overall performance of ionospheric radio networks. It is believed that careful consideration of the wave polarization effects in the design of reliable and efficient communication and broadcasting networks can result in relatively lower transmitter power and in the reduction of the number of channels occupied by a particular station.     

Diffraction by a rectangular groove with resistive walls

The plane wave diffraction from a rectangular groove having resistive vertical walls with material loading is analyzed for E polarization by using the Fourier transform technique. The problem is formulated into a modified Wiener–Hopf equation applying boundary conditions. The modified Wiener–Hopf equation is solved via the factorization and decomposition procedure. The scattered field is evaluated by taking the inverse Fourier transform and applying the saddle point method. Numerical results on the backscatter radar cross-section (RCS) patterns are presented for various physical parameters.     

极化智能天线的二维矢量波束形成方法研究

针对智能天线的匹配接收与干扰抑制等问题,将现有的基于均匀线阵的极化波束形成方法拓展到二维平面阵,提出了一种基于二阶锥规划的二维极化波束形成方法。在二维观测平面内,该方法通过对主瓣区域进行极化匹配设计以提高系统接收增益和主瓣干扰的抑制能力,在旁瓣区域将零陷凹面与极化约束进行叠加设计以最大限度提高干扰抑制能力,并建立最优的矢量波束优化模型,进而转化为两个等价的标量优化问题,可使用二阶锥规划求解。仿真结果表明:相对于现有的均匀线阵极化波束形成方法而言,该方法能够在方位-俯仰的二维平面上实现极化波束的约束优化,包括了主瓣极化匹配、零陷凹面的极化约束,提高了极化波束形成方法的工程实用性。      

Rayleigh-Sommerfeld and Helmholtz-Kirchhoff integrals: applicationto the scalar and vectorial theory of wave propagation and diffraction

Approximations for known integral solutions of the scalar Helmholtz equation (the Rayleigh-Sommerfeld (RS) integrals of type I and II) are discussed. The validity range of the approximated RS I integral for large, but finite distances from the boundary plane is calculated as a new result. The scalar Kirchhoff boundary conditions leading to a rough approximation of an aperture diffraction problem are inspected, and a new spatial frequency solution in the aperture plane is given. Published measurements and known approximate vectorial boundary values formulated with the Hertz vector are compared with the outcome of the traditional Kirchhoff theory. For the field propagating from light waveguide endfaces into a homogeneous medium, the polarization effects in the far-field are considered by approximating the near-field for weakly guiding fibers with a Hertz vector ansatz. Comparison with measurements shows that the polarization induced asymmetry of the far-field is small in comparison with the experimental uncertainties. Finally, the proper applications for the RS I; II integrals are clarified as opposed to using the scalar or vectorial Helmholtz-Kirchhoff integral     

A Novel Approach to Over-Rooftop Multiple Diffractions by an Array of Buildings of Arbitrary Height and Spacing for Mobile Radio Wave Propagation

A new approach to obtain field at the receiver due to multiple over-rooftop diffraction by an array of buildings with irregular height and spacing is presented. In the literature, the available approach is based on ray-tracing method that requires higher order diffraction coefficient (slope diffraction). The proposed method is efficient in the sense that it does not require higher order diffraction term to compute field strength. The method is validated by comparing the predicted results with available measurements and earlier results from the literature.     

A direct derivation of a single-antenna reciprocity relation for the time domain

In this paper, a single-antenna reciprocity relation is derived for the time domain. First, the antenna is considered on transmission; next, the same antenna is considered when it is receiving an incident plane wave. The two states, transmission and reception, are related by the application of a modified form of the reciprocity theorem for electromagnetic fields with general time dependence due to Cheo. The derivation of the reciprocity relation for the antenna makes use of simple geometric arguments to evaluate the spatial/temporal integrals that occur in the theorem. A few extensions of the reciprocity relation are also described.     

Feed network for dual beam reflector antennas

A primary feed network for doubly curved shaped-beam reflector antennas is described which allows simultaneous signal reception on two distinct elevation plane patterns such that the underside falloff separation between a fixed lower beam and a higher beam can be substantially varied in a lossless manner. A three-element feed array is employed wherein two elements of the array are interconnected by means of a sum-difference hybrid. The sum port generates the fixed low beam while the difference port generates an orthogonal beam pattern suitable for RF combining with an independent high beam generated by the third array element. Adjustment of the combining amplitude and phase relationships permits the variation of the underside falloff separation. The fixed low beam is, of course, also used for transmission at high power. Design parameters for a typical surveillance radar application axe discussed for a linearly polarized case. Calculated antenna patterns and free-space coverage diagrams are presented. The complexities of extending the feed network concept to handle switchable linear/circular polarization cases and an integral directional beacon pattern for L band systems are indicated.     

有限厚导电平板上任意缝隙的耦合特性分析

利用边界积分方程法结合广义网络原理和连接算法分析了有限厚导电平板上任意二维缝隙的散射及传输特性,并以ＴＥ波为例给出了具体的分析方法和结果。该方法不仅可用于任意形状和复杂介质填充缝隙的分析,还可考虑缝所在导体板的厚度。边界积分方程和连接算法的采用,使得分析该问题所需的计算机容量大大降低,计算效率大大提高。     

Diffraction of electromagnetic waves by the boundary of a semi-infinite metamaterial

Diffraction of plane waves at the interface of two semi-infinite regions is considered for the case when one of the regions is filled with a metamaterial in the form of a 3D periodic lattice of dipole-type particles. The diffraction problem is solved via the method of compensating sources, which is extended to the case of 3D structures. Different formulations of the diffraction problem that is reduced to either a system of Wiener-Hopf functional equations or a system of linear algebraic equations are presented. Representation of a semi-infinite structure by a sequence of layers characterized by wave transmission matrices is analyzed. It is shown that such matrices can be used to obtain the solution to the diffraction problem in an explicit form.     

线列红外偏振成像系统的设计

作为近年来偏振探测技术研究的新热点,焦平面分割型偏振探测器在增强目标与背景对比度和伪装目标识别方面具有明显效果。基于线列短波红外微偏振探测器,设计了一种以Jetson TX1 为处理核心的成像系统。该系统主要包括控制模块和处理模块。其中,控制模块由探测器驱动板和FPGA控制板构成〗,用于实现探测器信号AD转换和图像信号usb传输等;处理模块采用Jetson TX1平台,用于实现图像信号usb接收、积分时间调节、非均匀性校正、偏振度计算以及GPU并行算法。开展了目标场景红外与偏振成像实验,获得了分辨率为500×268的红外图像和红外偏振图像。     

Geometrical optics exact solutions for two classes of dielectricwedge structures

Two classes of dielectric wedges with a common edge are considered. For a certain direction of incidence and polarization of the primary plane wave, conditions are given under which total transmission occurs at all interfaces, i.e., the edge does not scatter and geometrical optics is the exact solution to the boundary value problem     

LiNbO3晶体中光折变光栅各向异性衍射的定量研究

对LiNbO3晶体中光折变光栅的各向异性衍射进行了定量研究。基于有效电光系数非零和布拉格相位匹配条件,对在LiNbO3晶体中各向异性衍射的衍射效率与光束偏振态和写入几何的关系进行了较为详细的理论计算和分析,根据建立的数学模型进行了数值计算,发现光轴垂直于写入平面时,写入的光栅可发生显著的各向异性衍射。实验测量与理论计算结果基本符合。     

腔基微带天线的矢量有限元--边界积分方法分析

该文将矢量有限元——边界积分(Edge-Based FE-BI)混合方法用于腔基微带贴片线的辐射特性分析。分别计算了在无阻抗负载和加有阻抗负载两种情况下的输入阻抗，以此验证了该混合方法的正确性；然后计算了贴片天线表面缝隙部分的场分布，验证微带天线分析模型——传输线模型的合理性；最后计算了E面、H面方向图以及相应的交叉极化方向图。     

A high gain dielectric loaded biconical horn for circular polarization

The experimental results of the radiation characteristics of a dielectric loaded biconical horn which radiates circular polarization are presented. The test horn was designed to radiate circular polarization in theXband. It is seen that the pattern directivity of the biconical horn in the vertical plane is significantly increased due to dielectric loading, and a desired beamwidth in the vertical plane may be obtained by a suitable dielectric loading.     

Two time-derivative Lorentz material (2TDLM) formulation of aMaxwellian absorbing layer matched to a lossy medium

A two time-derivative Lorentz material (2TDLM) is introduced to define polarization and magnetization fields that lead to an absorbing layer that can be matched to a lossy dielectric medium. The 2TDLM is a generalization of the successful uniaxial polarization and magnetization time-derivative Lorentz material (TDLM) which has been introduced as an absorbing boundary condition for simulation regions dealing with lossless materials. Expressions are derived to describe the propagation of an arbitrary plane wave in this 2TDLM Maxwellian absorbing material. They are used to study the scattering from a semi-infinite 2TDLM half-space of an arbitrary plane wave incident upon it from a lossy isotropic dielectric medium. Matching conditions are derived which produce reflectionless transmission through such an interface for any angle of incidence and frequency. Numerical tests are given which demonstrate the effectiveness of the resulting 2TDLM absorbing layer     

光折变局域体全息柱透镜变波长读出下的波前转换

研究了用波长为632.8nm的柱面波与平面波记录形成的体全息柱透镜用波长为800nm的平面波重现下的波前转换情况。结合二维耦合波理论,推导了形成于LiNbO3双掺杂晶体中该全息柱透镜的耦合波方程,并求出了其积分形式的解析解,分析了改变读出波长下该透镜的布拉格失配因子的分布情况,讨论了它的几何尺寸和记录柱面光波对其衍射效率的影响,以及柱面衍射光振幅在出射口径上的分布情况。结果表明,记录所形成的全息柱透镜的焦距越长它的衍射效率越高;该透镜厚度的增加会使它的衍射效率增加,但是透镜的衍射口径增加它的衍射效率会降低;衍射光振幅在其出射口径上的分布出现了一定程度的失真,衍射光强度主要集中分布在布拉格失配值较小处对应的位置。最后,进一步讨论了全息透镜记录过程中满足布拉格匹配条件的参考点的选择对光栅衍射性质的影响,结果表明衍射效率不随参考点的改变而改变。     

Maltese-cross coaxial balun-fed antenna for GPS and DCS1800 mobile communication

A novel antenna in the shape of a Maltese cross has been developed for GPS satellite and DCS1800 personal communication system application. This antenna exhibits good circular polarization (axial ratio <2 dB) and impedance performance over a bandwidth wide enough to cover the frequency band for GPS and DCS1800 reception. The addition of an adjustable clamp and tapering of the shape of the radiating elements improved the overall design. The gain of this antenna has been sufficiently high to compensate for the power loss due to polarization mismatch for the reception of a linearly polarized GSM/DCS1800 signal. A modular design and integration approach is presented to obtain the circular polarization required for GPS application.     

利用激光偏振特性的电子散斑面内全场位移测量技术的研究

提出一种能够同时测量面内全场位移的电子散斑测量光路结构,解决了面内全场位移在瞬态和不可重复情况下无法测量的问题。将激光束分成四路照明光,分别安排在水平和垂直平面内,利用激光器的偏振特性安排光路,使水平平面内两束光的偏振方向相同,垂直平面内两束光的偏振方向相同,但这两个平面中的偏振方向又互相垂直。对转动圆盘内位移测量,取得了满意的结果,用一幅散斑图同时得到了表示水平和垂直分量的散斑条纹