利用多扇区介质透镜得到TM01模激励的圆锥喇叭笔形波束辐射

 给出了一种改善TM₀₁模辐射特性的方法，由不同厚度的扇区组成的介质透镜放置于圆锥喇叭口径处，适当地选择各个扇区的厚度，从而产生圆极化的轴向为极大值的远场方向图。推导出了该天线辐射场的解析公式，解析结果与数值模拟有较好的吻合。当工作频率为5 GHz时，天线的增益达19.6 dB，口径效率31.3%，具有15.8%的带宽(反射系数S11<0.2), 且适合于高功率辐射。     

径向双层介质加载圆波导的TE_(11)-HE_(11)模式转换天线

介绍了径向双层介质加载圆波导的TE_(11)-HE_(11)模式转换天线的设计原理、实验方法及结果。该模式转换天线由圆波导TE_(11)-HE_(11)模式转换器和辐射器组成:圆波导TE_(11)-HE_(11)模式转换器是在圆波导内沿径向加载两种不同介电常数的微波介质来完成模式转换,辐射器采用开口圆波导或小张角圆锥喇叭将HE_(11)模辐射出去。应用HFSS软件对设计的两种模式转换天线进行模拟优化,数值结果显示这两种天线在线极化和圆极化工作状态下其E面、H面辐射方向图在一定波瓣宽度内均具有较高的等化特性及低副瓣电平。应用矢量网络分析仪和频谱分析仪对线极化TE11模激励状态下的两种模式转换天线的增益和驻波系数进行测试,测试结果表明:在中心频率9.4GHz频点辐射器采用开口圆波导或小张角圆锥喇叭时天线增益分别为11.21dB和15.58dB,且驻波系数均小于1.05。实测结果与仿真结果基本一致,证明了该模式转换天线技术的可行性与正确性。     

Sound propagation in two-dimensional waveguide with circular wavefront

Sound propagation through a waveguide is generally modeled by the Webster horn equation which assumes a planar pressure wavefront. However, most of the sources are non-planar in nature. In this work, a 1-D model is derived for sound propagation through a 2-D waveguide with circular wavefront. The model is derived from the 2-D Helmholtz equation using the weighted residual method. The model assumes a uniform pressure across the angular coordinate at a given radial distance. A 2-D finite element model is used to validate the results for different waveguide geometries and it shows good agreement.     

Wave reflections from duct terminations

The reflection coefficients and inertial end corrections of several duct terminations, including finite length duct extensions perpendicular to an infinite wall, as well as at a number of angles, curved interface surfaces, and annular cavities, are determined and analyzed in the absence of flow by employing the boundary element method. Predictions for the classical unflanged and flanged circular ducts show good agreement with analytical and computational results available in the literature. The predictions for curved interface surfaces (bellmouth or horn) are also consistent with the available experimental data. In view of its high reflection coefficient, the duct termination with an annular cavity may be suggested for the suppression of noise radiation in a specific frequency band or for an effective wave reflection from the termination.     

Millimeter wave beams diffracted from reflecting gratings

According to the angular-spectrum method, a radiation beam of an antenna horn in the Fresnal region is decomposed into the plane waves with the fast Fourier transform algorithm and the waves diffracted from a reflection grating are superposed as a diffracted beam. Compared with the reflected beam from the same size mirror, the radiation half width of the diffracted beam from a grating is narrower and its lateral shape is shift. These performances have been experimentally verified at Ka-band by: (1). The relative diffraction efficiencies in the first order with two triangular gratings which is put along propagating direction of a beam produced by a conical lens-horn. (2). H-plane lateral width with power—3dB lapsed of the focus beam from a grating and a mirror in a grating spectrometer for millimeter waves (25–100 GHz).     

Acoustic particle velocity horns

The paper considers receiving acoustic horns designed for particle velocity amplification and suitable for use in vector sensing applications. Unlike conventional horns, designed for acoustic pressure amplification, acoustic velocity horns (AVHs) deliver significant velocity amplification even when the overall size of the horn is much less than an acoustic wavelength. An AVH requires an open-ended configuration, as compared to pressure horns which are terminated at the throat. The appropriate formulation, based on Webster's one-dimensional horn equation, is derived and analyzed for single conical and exponential horns as well as for double-horn configurations. Predicted horn amplification factors (ratio of mouth-to-throat radii) were verified using numerical modeling. It is shown that three independent geometrical parameters principally control a horn's performance: length l, throat radius R(1), and flare rate. Below a predicted resonance region, velocity amplification is practically independent of frequency. Acoustic velocity horns are naturally directional, providing maximum velocity amplification along the boresight.     

改进型COBRA透镜天线的设计

 设计了X波段COBRA透镜型天线，利用电磁波在不同介质传播速度的差异，通过放置于圆锥喇叭口径处不同厚度的介质透镜改变TM₀₁模不同扇区的相位，从而改变TM₀₁模在普通喇叭口径处的轴对称分布，将轴对称的口径场分布转换为线对称，进而实现线极化或圆极化的轴向辐射。通过添加匹配介质，减小介质对微波的反射和驻波特性的影响；延伸喇叭到透镜边缘，使移相过程在波导内完成，有效地控制了电磁场模式。天线增益在中心工作频率为9.3 GHz时为19 dB，口径效率25%，辐射效率大于90%，反射系数小于1.3，轴比小于2 dB, 3 dB相对带宽大于30%，几乎可以覆盖整个X波段。     

基于Zemax分析双包层光纤吸收效率的新方法

计算双包层形状对光纤吸收效率的影响,常用的方法有二维射线法、三维射线法、光纤光学波动耦合理论等。介绍了一种基于Zemax软件计算其吸收效率的三维方法,通过编写ZPL宏计算了圆形、偏心形、矩形、D形、八角形等常规内包层形状对光纤吸收效率的影响,并将分析结果与二维射线法所得结果进行比较,数据表明:本文的计算结果和二维射线法的计算结果类似,各种内包层形状光纤的吸收效率趋势是一样的。它的优点在于本文给出的是吸收效率和光纤长度的关系,更形象直观,而二维射线法给出的是吸收效率和反射次数的关系;在Zemax中可以设置光线的临界角,而二维射线法是假设光线从内包层里任意一点随机发射的,它没有考虑到光线在内包层中发生全反射的条件,本文的计算结果更准确一些;在Zemax里可以构建各种内包层形状,它的非序列光线追迹速度很快,以矩形内包层光纤为例,在同样的条件下利用Zemax用时373 s,利用二维射线法用时1 732 s,所以基于Zemax分析双包层光纤吸收效率的方法计算速度更快。最后用这种方法研究了上海光机所楼祺洪研究员提出的一种新型双包层光纤的吸收效率。     

E面和H面方向图等化的双模圆锥喇叭设计

 介绍用于Φ7.3 m Cassegrain天线的高功率馈源喇叭的设计。为使E面和H面方向图在照射区域内具有高的等化度，选择双模圆锥喇叭作为馈源的结构形式。由于高功率源采用BJ-32波导输出信号，故馈源系统中还应包含一个矩形到圆形的模式转换器，将TE10模转换为TE11模。设计了双模圆锥喇叭和模式转换器，并进行了功率容量估算。测试结果表明，所设计的馈源达到了设计要求，理论计算结果和实验测试数据吻合良好。     

Rigorous solutions for sound radiation from circular ducts with hyperbolic horns or infinite plane baffle

A rigorous treatment is presented of sound radiation from circular ducts with either a hyperbolic horn or an infinite plane baffle. In the analysis hyperboloidal wave functions are used, which are defined here, for the first time, as a class of eigensolutions of the wave equation for oblate spheroidal co-ordinates. The numerical results include the complex conversion (or reflection) coefficients and the radiation directivity for various incident wave modes, spinning modes as well as axisymmetric modes. The solutions are valid for the whole frequency range including frequencies above and below the cut-off frequencies of the duct modes involved.     

Shift operator method and Runge-Kutta exponential time differencing method for plasma

In this paper, the shift operator finite difference time domain (SO-FDTD) method and Runge-Kutta exponential time differencing (RKETD) method are introduced. The high accuracy and efficiency of the two methods are verified by calculating the reflection and transmission coefficients of electromagnetic waves through a collisional plasma slab. A comparison of computational efficiency of the two methods is presented by simulating the electromagnetic wave propagation in homogeneous non-magnetized plasma. The numerical results indicate that the calculation time using SO-FDTD method is less than that using RKETD method with almost the same accuracy.     

Subwavelength structures for broadband antireflection application

The subwavelength structures are designed and fabricated for broadband antireflection application. Under target of zero reflectivity, the parameters of periodic 2-D continuous conical structures are analyzed by the finite-difference time-domain (FDTD) method. The corresponding conical structures are obtained with spatial period of 350 nm and structure height of 300 nm, respectively. The 2-D continuous conical structured surface is fabricated by micro-replication process combining with the originated structure fabrication realized by interference lithography, Ni mold electroplation and replication by using UV imprinting into plastics. The average reflectances of the simulation and replicated polymer prototype are about 0.50% and 0.54% within the spectral ranges of 400-650 nm, respectively. In a word, the subwavelength structured surface with low reflection is developed and proved to be highly consistent with the simulation results.     

Quasioptical Approach for Meniscus Lens Corrected Horn: Application to Cassegrain Systems

The Beam Mode Expansion (BME) approach for corrugated conical feed horn plus meniscus lens is presented. This approach is useful for providing the radiation pattern as it propagates through an optical system. A developed theoretical model has been verified measuring near and far field of a built horn and lens. These results have been used for designing the optical system of a Cassegrain antenna at 100GHz using the fundamental Gaussian beam mode (GBM) of the new approach. Multimode analysis has been performed with the pre-designed system in order to test the fundamental GBM results.     

水平极化光在单轴吸收晶体中的传播

根据光在各向同性吸收介质中传播的分析方法,引入了波法线矢量传播常量,讨论了水平极化光在单轴吸收晶体中的传播规律,得到了波法线折射率、光线折射率、吸收系数等描述吸收晶体性质和光传播性质的物理量的表达式,推导出透明晶体的相应公式.数值计算表明,由该法得到的晶体表面的反射和透射系数与用复折射率表示法得到的结论一致.     

Diffraction at a surface-impedance discontinuity in a closed waveguide

The Wiener-Hopf-Fock method is applied to a coaxial waveguide for which the impedance boundary conditions are given for one surface. Closed expressions are obtained for the moduli of the reflection and transmission coefficients, from which the characteristics of circular and rectangular guides may be deduced. These coefficients are expressed in formally identical ways for all closed systems. Transition to the limit of an open system is considered for a circular cylinder.     

Analysis of a conical horn fed by a slightly oversized waveguide

This paper discusses the case of a submillimetre conical feedhorn system which is overmoded due to an oversized waveguide, but is not in the geometric optics regime. The motivation for this system is to use the same feed as a multi-frequency receiver. Increased background loading is the greatest disadvantage in overmoded optics; and aperture efficiency also suffers due to non-optimum horn dimensions. The analysis is done using the Laguerre-Gauss beam expansion method.     

带有锥形孔的复合变幅杆设计及动态分析

在超声振动拉丝加工过程中,为了实现线材的顺利拉拔,需要应用带有锥形孔的复合变幅杆。为此,本文基于等效四端网络与传输矩阵法,建立了带锥形孔圆锥变幅杆的传输矩阵,推导出带锥形孔圆锥过渡复合变幅杆的频率方程的一般公式。根据推导出的频率方程,应用区间搜索法和牛顿迭代法获取了准确的数值解,实现了该复合变幅杆的纵向振动。之后,应用有限元软件Ansys对设计出的复合变幅杆分别进行模态分析和动力学特性分析,获得了各段不同长度下复合变幅杆谐振频率、放大系数以及最大应力值的变化规律。最后,对制造出的复合变幅杆进行阻抗与振动性能测试,结果表明其频率准确,且振幅比较稳定。     

Ka波段高功率斜角弯头的设计

介绍了一种基于准光技术的高功率斜角弯头的设计方法,可实现圆波导TE0m模式的高效转弯传输。使用模式变换器将工作模式TE0m转换成锥形高斯模,经过转弯后,锥形高斯模被重新转换成工作模式。这种锥形高斯模可以减少波束在镜面的衍射,从而实现工作模式的高效率转弯传输。基于这一方法,设计了工作在Ka波段、工作模式TE01的MW级波导斜角弯头。HFSS计算结果表明: 在8%的带宽内,传输效率大于98%。     

Reflectance of acoustic horns and solution of the inverse problem

A method is described for solving the inverse problem of determining the profile of an acoustic horn when time-domain reflectance (TDR) is known only at the entrance. The method involves recasting Webster's horn equation in terms of forward and backward propagating wave variables. An essential feature of this method is a requirement that the backward propagating wave be continuous at the wave-front at all locations beyond the entrance. Derivation of the inverse solution raises questions about the meaning of causality in the context of wave propagation in non-uniform tubes. Exact reflectance expressions are presented for infinite exponential, conical and parabolic horns based on exact solutions of the horn equation. Diameter functions obtained with the inverse solution are a good match to all three horn profiles.     

A finite element method for transmission in non-uniform ducts without flow: Comparison with the method of weighted residuals

A finite element method is developed for the study of transmission of sound in non-uniform ducts without flow. The formulation is based on a weighted residual approach and eight noded isoparametric elements are used. Two computational schemes are described, one based on the Helmholtz equation obtained by combining the basic conservation equations and one based on the conservation equations themselves. The latter case is considered because in future extensions to problems involving mean flow a single governing equation is not readily obtainable except for irrotational flows. Both two-dimensional and circular duct geometries are considered. Comparisons are made with a Method of Weighted Residuals in the form of a Modified Galerkin Method in the two-dimensional case to assess both accuracy and computational efficiency. It is found that the finite element method produces results for transmission and reflection coefficients nearly identical to those from the Galerkin approach. Used to its best advantage the finite element method is of comparable efficiency.