Analysis of helical slow-wave structures for space TWTs using 3-D electromagnetic simulators

This paper presents a detailed analysis of traveling wave tube (TWT) helical slow-wave structures (SWSs) using three-dimensional (3-D) electromagnetic simulators. The main advantages of this approach are its capability to take into account the real 3-D geometry of this complex structure, and consequently to eliminate the approximations used in the analytical approach. In addition, it provides higher accuracy than experimental results. Two different methods have been applied (finite elements and finite integration) to predict the cold parameters (phase velocity, coupling impedance, and attenuation) at a level of accuracy higher than the usual practice. An extended analysis has been performed to guarantee the stability and accuracy of the results, as well as to study the sensitivity of the results to the discretization. This paper has shown that both methods, as implemented in two commercially available simulators, are perfectly suitable for the accurate modeling of such complex geometries.     

基于噪声子空间映射的二维波达角快速估计算法

为了降低二维MUSIC(Two Dimensional Multiple Signal Classification,2-D MUSIC)算法的计算量,提高算法的实时处理能力,基于噪声子空间映射思想提出了一种适用于任意平面阵列结构的二维波达角(Direction Of Arrival,DOA)快速估计算法.新算法利用空间角度划分及非线性变换将信号子空间与噪声子空间的正交性等价地压缩至某个角度分片内,使得真实DOA在该角度分片内产生虚拟镜像,通过搜索该角度分片得到虚拟DOA,最后利用数学式直接计算得到真实DOA.理论分析和实验结果表明新算法能够成倍地提高DOA估计的速度,同时具有比MUSIC算法更高的空间分辨率.     

The wave-equation FD-TD method for the efficient eigenvalueanalysis and S-matrix computation of waveguide structures

A modified finite-difference-time-domain (FDTD) formulation based on the direct discretization of the vector wave-equation is applied to the efficient analysis of hybrid-mode waveguiding structures. For both 3-D and 2-D waveguide eigenvalue problems, the formulation requires only one grid, and just the solution of three coupled equations is necessary. Numerical examples concerning the resonant frequencies for an inhomogeneously filled waveguide resonator as well as the fundamental- and higher-order-mode propagation factors for insulated image guides, shielded coupled dielectric guides, and lateral open dielectric ridge guides demonstrate the efficiency of the method. The theory is verified by comparison with results obtained by other methods     

Susceptibility analysis of wiring in a complex system combining a3-D solver and a transmission-line network simulation

This paper deals with the application of electromagnetic field-to-transmission-line coupling models for large cable systems analysis. It emphasizes the use of Agrawal's (1980) model applied here in a numerical simulation of an electromagnetic susceptibility problem up to 500 MHz. Based on the concepts of EM topology, the proposed methodology consists in calculating the incident fields with a three-dimensional (3-D) computer code and the coupling on cables with a multiconductor transmission-line network computer code. In order to validate the efficiency of this methodology in an industrial context, an experiment has been performed on a prototype wiring installed in a Renault Laguna car, stressed by an EM plane wave. Numerous validation configurations have been carried out. First, the prototype cable network under study has been tested on a ground plane to validate the coupling model but also, to validate the cable-network topology itself. Second, EM fields have been measured onto the structure and inside the structure. Then, they have been compared to 3-D calculations, performed with an FDTD code. Third, comparisons between measurements and calculations of bulk currents and voltages on 50 Ω loads on the wiring have been achieved     

Reduction in Reflections and Ground Bounce for Signal Line Over Slotted Power Plane Using Differential Coupled Microstrip Lines

This paper investigates the noise reduction in the slot-induced ground bounce noise by using differential signaling. An efficient 2-D finite-difference time-domain method together with equivalent circuits for both the differential line and the slot is established and simulations are performed for a three-layer structure to characterize the ground bounce coupling. A simple model is then proposed to understand how the differential coupled microstrip lines can help reduce ground bounce. Different factors which affect noise reduction are investigated, such as the coupling coefficient, rising time, skew of differential signaling, and structure asymmetry in slotline. An experimental setup is devised to demonstrate the noise coupling between signal lines due to the slot-induced ground bounce and significant noise reduction by employing differential signaling. A favorable comparison between the simulation and measured results validates the proposed equivalent circuit model and analysis approach.      

Rigorous analysis of multiple coupled rib waveguides

The general problem of multiple coupled rib waveguides, where energy may be leaked from one guide to the other via the substrate and radiation mode, is treated. Rigorous results including substrate and air modes coupling are sought for the general case of coupling of two or more different guides. The analysis, developed in terms of a cascade of the transverse steps, utilizing a variational solution with a single trial function and making explicit use of edge singularities at the dielectric corners in order to produce an effective and rigorous solution, is presented. Multiple coupled rib guides are then reduced to a cascade of interacting step discontinuities in the transverse direction. When comparison is possible, the numerical results obtained by the method are seen to be as accurate as those obtained by the finite element method (FEM)/finite difference method (FDM), but with a fraction of the computer time and memory involved     

Analysis and measurement of mode polarizers in square waveguide

A general analysis approach for strip metallization structures enclosed in rectangular or square waveguide is presented. The technique involves the novel application of a commercially available 2.5-dimensional (2.5-D) method-of-moments-based (MoM) electromagnetic (EM) analysis tool to a three-dimensional (3-D) waveguide problem. Very good agreement is demonstrated between computed and measured results for several printed strip linear polarizers embedded within a square waveguide environment. This paper, to the authors' knowledge, represents the first such comparison of phase and magnitude between computed and measured data for strip grid polarizers in a waveguide environment. The developed approach involves construction of a theoretical waveguide “test fixture” and an associated theoretical de-embedding procedure. Computational advantages are expected over the alternative approach of using a finite-element-based fully 3-D analysis approach. The polarizer results have potential application to shielded versions of quasi-optic array components that have been demonstrated in open geometries, as well as to multimode antenna feeds, waveguide filters, and matching networks     

A simple analysis of single- and double-V-groove guides

Single- and double-V-groove guides are analyzed by an approach based on a combination of the transverse resonance method and the numerical integration technique. Comparisons between the predicted results and available measured results for a single V-groove guide show good agreement. The new approach is simple and accurate. Numerical results for the coupling characteristics of a double-V-groove guide are also presented     

On the mode coupling in longitudinally magnetized waveguidingstructures

Propagation in waveguiding structures containing gyromagnetic material with longitudinal magnetization is analyzed in terms of the coupling between modes having different symmetry properties. It is found that the wave supported by a symmetrical structure of two coupled guides is a combination of the even and odd modes propagating in an isotropic structure. The gyromagnetic medium causes the coupling between the modes, and the energy of the wave is periodically transferred from one mode to another, which in turn results in the exchange of energy between guides. The proposed mathematical model explains the operation of novel nonreciprocal devices     

Coupling Between an Abruptly Terminated Optical Fiber and a Dielectric Planar Waveguide

The coupling between an optical fiber and a dielectric planar waveguide is analyzed when both guides are terminated abruptly and are facing each other. Mixed spectrum eigenwave representations of fields are employed inside the waveguides while Fourier integrals are utilized to describe the field in the space between the two guides. A coupled system of integral equations is derived by satisfying the boundary conditions on the terminal planes of both waveguides. A weak guidance approximation is assumed to facilitate the analysis. Numerical results are presented for several coupling geometries. Misalignment losses and coupling optimization phenomena are investigated.     

非线性相位耦合的切片谱分析方法

本文提出利用１１／２维谱方法对二次相位耦合进行了分析，该方法同原有双谱方法相比具有计算量小，执行简便，易于获得较高的分辨率等优点，本文还将二次相位合的研究拓广到复数域，根据积累量的不同定义方式得到了不同的结果，最后本定义了２１／２维谱，对另外一种重要的非线性相位耦合－三次相位耦合进行了分析，取得了良好的效果，仿真实验验证了文中结论。     

Tapered, both in dimension and in index, velocity coupler: theoryand experiment

The authors consider a tapered velocity coupler (TVC) that meets the adiabatic invariance condition with sufficiently strong coupling between the fundamental modes of individual guides in the middle region of the coupler while permitting individual excitation at the input end and sorting of the modes at the output end. This approach helps reduce the device length considerably by permitting much higher taper angle. A TVC consisting of one tapered and another straight, graded index waveguide is modeled using the normal modes of the entire, composite TVC structure. The analytical results are in excellent agreement with experimental results for a TVC fabricated in Ti:LiNbO₃. It is shown that the representation of the local normal modes as the superposition of the modes of the uncoupled guides leads to erroneous results     

PSTM/NSOM modeling by 2-D quadridirectional eigenmode expansion

A two-dimensional (2-D) model for photon-scanning tunneling microscopy (PSTM) of integrated optical devices is evaluated. The simulations refer to a setup where the optical field in the vicinity of the sample is probed by detecting the optical power that is transferred via evanescent or radiative coupling to the tapered tip of an optical fiber close to the sample surface. Scanning the tip across the surface leads to a map of the local optical field in the sample. As a step beyond the mere analysis of the sample device, simulations are considered that include the sample as well as the probe tip. An efficient semianalytical simulation technique based on quadridirectional eigenmode expansions is applied. Results for a series of configurations, where slab waveguides with different types of corrugations serve as samples, allow assessment of the relation between the PSTM signal and the local field distribution in the sample. A reasonable qualitative agreement was observed between these computations and a previous experimental PSTM investigation of a waveguide Bragg grating.     

Study of 3-D magnetic components by means of "double 2-D" methodology

The magnetic field in many magnetic components, namely toroids and EE cores, has a three-dimensional (3-D) distribution. Energy and losses calculation in these particular structures makes necessary the use of 3-D techniques that accounts for all 3-D effects. The calculation of the energy and losses is needed in order to obtain any transformer model. This paper presents a procedure that allows the calculation of energy and losses in 3-D structures using two-dimensional (2-D) approaches. This procedure accounts for 3-D effects, solving each magnetic component by means of two different analyses but using 2-D finite-element analysis (FEA) solvers instead of 3-D. The main advantages of this procedure are that all geometrical and frequency effects are taken into account using 2-D FEA solvers. 3-D FEA solvers are not applicable to analyze most practical cases because of the complexity in the geometry. Therefore, the use of this method is not only advantageous from the point of view of time reduction, but also it is a solution for many cases where 3-D solvers are not a feasible solution. Some experimental results illustrate the application of the methodology, which is especially useful to study the influence of the winding strategy in toroidal structures and to design integrated magnetics in order to adjust the coupling coefficient between each pair of windings before the component construction.     

Impact of Mutual Coupling on Adaptive Switching Between MIMO Transmission Strategies and Antenna Configurations

Adaptive switching between multiple-input multiple-output (MIMO) transmission strategies like diversity and spatial multiplexing is a flexible approach to respond to channel variations. It is desirable to obtain accurate estimates of the switching points between these transmission schemes to realize the capacity gains made possible by adaptive switching. In this paper, it is shown that the accuracy of switching point estimates for switching between statistical beamforming and spatial multiplexing is improved by taking into account the effects of mutual coupling between antenna array elements. The impact of mutual coupling on the ergodic capacities of these two transmission strategies is analyzed, by deriving expressions for the same. Adaptive switching between combinations of transmission strategies and antenna array configurations (using reconfigurable antenna arrays) is shown to produce maximum capacity gains. Expressions for the switching points between transmission strategies and/or antenna configurations, including mutual coupling effects, are derived and used to explore the influence of mutual coupling on the estimates. Finally, measurements taken from reconfigurable rectangular patch antenna arrays are used to validate the analytical results.     

New design of 2-D photonic crystal waveguide couplers

Optical couplers arei mportant componentsinthe sys-temof optical signal processing,optical communicationand optical calculation.Therefore many people areinter-estedinseekingfor those couplers with uniquefunction.Photonic crystals (PC)[1-2]have drawn great…     

球面分布的半导体激光二极管阵列泵浦结构的研究

一个用来泵浦的半导体激光二极管堆栈包括8个半导体激光二极管阵列。这些阵列排布在一个球面上,每个bar条的输出激光被离轴压缩来实现高效率的耦合。半导体激光二极管堆栈的输出光束由一个空心导光管耦合到激光工作介质上。针对用于耦合半导体激光二极管堆栈的空心导光管进行了几何光学和光线追迹的分析。几何光学的分析揭示了耦合损耗的原因,并用来指导结构的设计。光线追迹分析结构参数和泵浦系统的输出特性,用来指导耦合系统参数的优化。模拟和分析结果表明,将半导体激光二极管阵列排布程球面可以提高偶和效率,降低最优化的导光管长度,改善输出能量场的分布。     

Three-Dimensional Urban EM Wave Propagation Model for Radio Network Planning and Optimization Over Large Areas

A new 3-D urban electromagnetic wave propagation model is presented. It provides fast 3-D deterministic predictions in urban radio configurations and over large areas. The various techniques to make it suitable to the network planning and optimization of large wireless networks are described. The resulting radio propagation maps exhibit seamless coverage between the various environments (dense urban, urban, and suburban). The model efficiently addresses all types of outdoor transmitter configurations (macrocells, minicells, microcells, and picocells) and all types of receiver locations (at ground level, over the rooftop, and at high building floors). It predicts the field strength as well as the dominant specular contributions of the impulse responses to build ray spectra (including delays and angles). Thus, the model may also be used to estimate the performances of new radio systems [diversity and multiple-input–multiple-output (MIMO)]. The narrowband power prediction of the model is evaluated by comparison with microcell measurements. The evaluation stresses the advantage of 3-D modeling compared with the vertical-plane approach or 2-D ray tracing. Finally, the ability of the model to simulate radio wideband characteristics in a complex environment is demonstrated by comparing delay-spread estimates to measurements collected from a high-macrocell transmitter in a hilly city and to arrival angles collected in a suburban macrocell area.      

Disk and ring microcavity lasers and their concentric coupling

Structures of concentric microdisk and rings were studied theoretically and experimentally. A three-dimensional (3-D) model was developed, emphasizing the possibility of coupling several concentric microresonators. The 3-D analysis resulted in closed-form analytic expressions for the six field components from which the limitations and necessary conditions for concentric coupling were derived. We emphasized the important differences between our results and the predictions of the more commonly used two-dimensional models-the latter are failing to predict the concentric coupling actual feasibility. Finally, we present experimental results of coupled ring vertical-cavity surface-emitting lasers, revealing a good match to the 3-D model predictions     

Electromagnetic wave effects on microwave transistors using afull-wave time-domain model

A detailed full-wave time-domain simulation model for the analysis of electromagnetic effects on the behavior of the submicrometer-gate field-effect transistor (FET's) is presented. The full wave simulation model couples a three-dimensional (3-D) time-domain solution of Maxwell's equations to the active device model. The active device model is based on the moments of the Boltzmann's transport equation obtained by integration over the momentum space. The coupling between the two models is established by using fields obtained from the solution of Maxwell's equations in the active device model to calculate the current densities inside the device. These current densities are used to update the electric and magnetic fields. Numerical results are generated using the coupled model to investigate the effects of electron-wave interaction on the behavior of microwave FET's. The results show that the voltage gain increases along the device width. While the amplitude of the input-voltage wave decays along the device width, due to the electromagnetic energy loss to the conducting electrons, the amplitude of the output-voltage wave increases as more and more energy is transferred from the electrons to the propagating wave along the device width. The simulation confirms that there is an optimum device width for highest voltage gain for a given device structure. Fourier analysis is performed on the device output characteristics to obtain the gain-frequency and phase-frequency dependencies. The analysis shows a nonlinear energy build-up and wave dispersion at higher frequencies