Ray-Optical Analysis of Electromagnetic Scattering in Waveguides

The ray-optical method presented previously for the analysis of scalarizable waveguide discontinuity problems is extended to vector scattering problems wherein an incident TE or TM mode excites both mode types. The procedure is illustrated first for reflection of an obliquely incident mode from the open end of a parallel plane waveguide, and is then applied to reflection from an open-ended circular waveguide. Formulas for modal reflection and coupling coefficients are given to various degrees of approximation, depending on whether or not multiple interaction phenomena are considered in addition to the simplest primary diffraction effects. Comparison with data computed from exact solutions for the circular waveguide problem shows that the ray-optical method is remarkably accurate not only in the strongly overmoded but also the dominant mode regimes.     

Mutual coupling analysis of a finite planar waveguide array

This paper deals with mutual coupling in a finite planar array antenna, composed of open-ended circular waveguides in a ground plane. The element-by-element approach is used and the problem is formulated as an integral equation, by requiring the transverse electric and magnetic fields to be continuous across the apertures. The equation is then solved by the method of moments and the mutual coupling in a 127-element array is computed. Excellent agreement with measurements and with the active reflection coefficient for the corresponding infinite array is found. The presented method of coupling analysis can be considered as a supplement to the established periodic-structure approaches for infinite arrays and may be useful for the analysis of small or nonperiodic arrays.     

互耦条件下米波雷达角度估计的自校正算法

针对互耦条件下米波雷达目标低角估计问题,提出了一种波达方向估计的自校正算法。分析了米波雷达在互耦条件下目标回波存在多径时的信号形式;利用均匀线阵互耦矩阵的特点对接收数据协方差矩阵的信号参数形式进行变换;在未知互耦校正信息的情况下,基于子空间原理得到目标波达方向的角度搜索函数,还推导出表面反射系数和阵列互耦矩阵的计算表达式。与同类校正算法相比,该算法在存在多径相干信号和未知互耦矩阵的情况下,不损失阵列孔径,不需要辅助阵元和校准源,且不需要迭代运算。仿真结果验证了该算法的有效性。     

基于互耦效应的相控阵天线有源反射系数研究

建立逼真高效的互耦效应分析模型对相控阵天线设计至关重要。阵列天线的互耦效应通常可以用有源反射系数显性化表征,分别采用无限阵仿真与散射(耦合)系数综合实验相结合的方法提取了阵列天线的有源反射系数。首先基于无限阵方法设计相控阵渐变开槽天线,优化并获取无限阵列环境下的中心单元有源反射系数,再依据设计结果研制169单元阵列天线,通过实验测试提取中心单元与其它各激励单元的散射系数的幅值与相位变化,最后采用散射(耦合)系数法综合出有限大阵列的有源反射系数。无限阵仿真结果与有限阵实测结果在扫描盲点出现角度、频段、有源驻波整体趋势等方面吻合良好,从而验证了无限阵设计方法在天线工程设计中的实际效果。     

米波雷达低仰角目标多径模型及其反演方法研究

现有的低仰角测高方法多采用镜面反射模型,将直达波与多径简化为两远场点源;然而实际中不规则反射面使多径回波波前畸变,远场点源模型难以完全描述多径信号。针对此模型失配问题,该文重点研究低仰角目标多径模型,首先分析经典多径模型,对反射系数和反射面高度进行参数反演;然后提出一种扰动多径模型,将反射面对多径回波的影响建模为扰动反射系数,并利用最大似然算法反演扰动反射系数。计算机仿真结果验证了参数反演方法的有效性;实测数据验证了复杂情形下所建模型的合理性和反演方法的有效性,提高了低仰角测高算法在实际阵地的适用性。     

Fresnel analysis of effective mirror reflectivity in folded-cavityin-plane surface-emitting lasers

Inside-cavity diffraction loss resulting from unguided regions and 45° internal total reflection mirror(s) is an important issue for fabricating folded-cavity in-plane surface-emitting lasers. A Fresnel plane-wave decomposition method was applied to analyze this problem. The effective reflectivity of an angle-etched mirror was calculated for deviation of the etched angle and different lengths of the unguided region. The results offer design criteria for fabricating folded-cavity surface-emitting lasers as well as other devices with angle-etched facet(s) for surface normal light coupling     

Numerical study of spot-size expanders for an efficient OEIC to SMFcoupling

Different types of spot-size converters are studied numerically, and their coupling loss and reflection properties are discussed in detail. The rigorous vector finite-element method is used to calculate the modal propagation properties and the least-squares boundary residual method is employed to calculate the coupling loss, reflection coefficient, and the alignment tolerances of the devices. It has also been observed that the reflection coefficient reaches a minimum when the mode confinement is at its maximum     

An optimization approach to the frequency-domain inverse problemfor a nonuniform LCRG transmission line

The inverse problem for a nonuniform LCRG transmission line is considered in the frequency domain. Imbedding equations for the reflection and transmission coefficients are derived through the concept of wave-splitting. An optimization approach is applied to reconstruct the line parameters as functions of the position using band-limited reflection and/or transmission data. Exact and explicit expressions for the gradients are derived, and the reconstruction algorithm (based upon a conjugate gradient method) is tested with both clean and noisy data, The problem of the nonuniqueness is also discussed     

Network model for strip-fed cavity-backed printed slot antenna

An equivalent network for the strip-fed cavity-backed slot antenna is derived. The model is based on some physical insight into the problem. The various parameters of the network are derived from the experimental data on the input reflection parameter of the antenna. This model gives an insight into the strip-slot-cavity coupling and hence the working of the structure. It is also useful for predicting the performance of such practical antennas.     

Method of determining the admittance loading of slot coupled T-junctions

A new method is presented for inferring the real and imaginary parts of admittance loading seen by the exciting guide of an H-plane slot coupled T-junction from measurement of the magnitudes of the reflection and coupling coefficients. These quantities are measured using an HP network analyser together with a reflection and transmission test unit, which provides better accuracy of measurement. A comparison between measured data with the theoretical values determined by the authors is presented.     

Coupling of Degenerate Modes on Curved Dielectric Slab Sections and Application to Directional Couplers

Approximate expressions are derived for the coupling of degenerate modes on two curved dielectric slab sections. From this analysis a directional coupler is designed in which a finite length coupler is joined to terminal lengths via curved structure sections. The reverse coupling (directivity) and reflection, as well as corrections to the coupling length, are studied. The propagation characteristics and the reflection coefficient due to coupling, as well as the correct 3-dB coupling length are calculated, numerically. Second order effects, that determine the band-width as well as the coupling, have been considered and found to be very substantial. In the examples considered the reflection and directivity due to the coupling process were both more than 35 dB down, and the 3-dB outputs were exactly in quadrature, correct to the first order of approximation.     

应用于无人驾驶车的激光雷达雪天去噪方法研究

针对雪花噪声对激光雷达造成误检的问题,提出了一种基于激光雷达反射强度和邻域搜索算法的综合方法对降雪场景采集的激光雷达点云数据进行去噪处理.首先通过自适应方法统计激光雷达点云数据的反射强度分布,计算点云的动态边界阈值.然后,通过分析点云数据反射强度与邻域搜索算法对雪花噪声进行滤除.本方法对园区降雪天气下的实际激光点云数据...     

Scattering from stacked gratings and dielectrics for various anglesof wave incidence

The theory of scattering matrices and microwave network analysis is used to solve the problem of scattering from cascaded infinite periodic gratings. The total reflection and transmission coefficients are calculated as functions of angle of incidence, wire spacing for each grating separation, wire thickness, and number of gratings that comprise the cascaded structure. The problem of stacking dielectric slabs with periodic gratings is also formulated and solved. In all cases, the secant corrector spectral iteration approach is used as a numerical method for calculating the desired currents and fields. Finally, the calculated values of the reflection and transmission coefficients are presented and compared with reported experimental and theoretical data     

TE111双模圆柱腔椭圆函数滤波器的耦合设计

滤波器是邻频频道合成器的关键部件之一,而耦合问题又是滤波器设计的关键.本文论述了TE111双模圆柱腔椭圆函数滤波器中应用的简并腔模及腔间与端面的耦合设计.文中巧妙地使用调谐螺钉和耦合螺钉,解决了双模圆柱腔椭圆函数滤波器中应用的简并腔模及腔间与端面的耦合设计问题,最后给出了该方法设计出的产品的实测数据.该产品使用效果好,用户满意.     

高速采集系统的时钟端接设计与仿真

高速采集系统中常用的交流耦合端接设计没有考虑单端阻抗匹配,使得单端时钟信号产生反射,反射噪声严重时会破坏系统的准确性.为了改善反射噪声,提出了一种改进的LVPECL差分信号端接设计,将单端阻抗匹配电路引入驱动端,从而达到抑制反射噪声的效果.仿真证明,当信号频率小于500 MHz时,与常用端接设计相比,改进端接设计的接收信号过冲最大减少了10.9％,反射噪声得到抑制,提高系统的稳定性和准确度.     

Mutual coupling, gain and directivity of an array of two identical antennas

It is shown that there is an optimum nonzero value of mutual coupling and passive reflection coefficient that is a function of only the embedded element pattern and element spacing. Optimum is defined as yielding maximum array gain. For closely spaced arrays, the optimum mutual coupling and passive reflection coefficient are quite large, but tend to cancel in the active mode to produce a low active reflection coefficient. A smaller value of mutual coupling would give lower gain than the optimum case. This again demonstrates that mutual coupling is a natural and desirable effect in array behavior. It is well known that it is possible to achieve array superdirectivity, in the sense that the directivity of an array of "N" elements is greater than "N" times the embedded element directivity; however, in this case the mutual coupling and passive reflection produce an active reflection coefficient that results in an array gain lower than "N" times the embedded element gain. In fact, higher superdirectivity always implies lower gain, relative to embedded element gain.     

基于实测地形的米波雷达测高方法

基于二次雷达高度信息对地形参数进行优化的合成导向矢量算法对米波雷达测高具有较高的精度,但在没有二次雷达信息的情况下,测高精度较低.鉴于此,本文提出了一种基于实测地形的测高方法,首先对目标方位的地形起伏进行遍历,通过球面模型计算得到对应的反射点距离,将其与真实反射点距离差值最小的位置作为真实的反射点位置,然后将其距离和地...     

Obliquely arranged feed waveguide for alternating-phase fed single-Layer slotted waveguide array

An alternating phase fed waveguide array with an oblique arrangement of feed waveguide is proposed. It belongs to single-layer waveguide arrays developed by the authors. Conventional arrays with radiation waveguides arranged perpendicularly to the feed waveguide suffer from accumulated reflection from coupling windows after round-trip propagation at the input port. In the proposed oblique arrangement, the reflections from each coupling window will not accumulate in phase but be diffused away out of phase. First, the design of obliquely arrayed T-junctions is conducted using two-dimensional finite element method (FEM). Then basic operations of the reflection canceling as well as improved voltage standing-wave ratio at the antenna input are confirmed by experiments. Almost the same radiation patterns and gain as the conventional arrays are observed in the measurements     

基于双向耦合补偿的超材料传输/反射法

在未考虑超材料中结构单元间耦合作用的情况下,传统传输/反射法在提取整体材料的等效电磁参数时会出现误差.针对该问题,对超材料中不同方向单元耦合及其补偿方法进行了讨论,提出一种基于双向耦合补偿的改进传输/反射法.与传统方法相比,该方法可有效预测超材料中多个谐振区域,更准确地提取整体材料参数;其仿真结果能与Ansoft HFSS软件计算结果很好地吻合;由于采用了局部建模,显著降低了其相应的计算时间及硬件要求.     

基于光波导的高耦合效率垂直耦合结构设计

针对目前光电印制板(OEPCB)中光电器件与光波导对接的垂直耦合结构耦合效率较低的问题,分析了传统嵌入式45°反射微镜的垂直耦合结构,提出了一种新的垂直耦合结构,经Matlab仿真验证其具有更高的垂直耦合效率。研究表明,新结构对光电对准精度要求不高,受传统PCB制作工艺的层压的高温高压影响更小、便于兼容传统PCB制作工艺。