Analysis of Millimeter Wave Scattering by an Electrically Large Metallic Grating Using Wavelet-Based Algebraic Multigrid Preconditioned CG Method

An effective wavelet based multigrid preconditioned conjugate gradient method is developed to solve electromagnetic large matrix problem for millimeter wave scattering application. By using wavelet transformation we restrict the large matrix equation to a relative smaller matrix and which can be solved rapidly. The solution is prolonged as the new improvement for the conjugate gradient (CG) method. Numerical results show that our developed wavelet based multigrid preconditioned CG method can reach large improvement of computational complexity. Due to the automaticity of wavelet transformation, this method is potential to be a block box solver without physical background.     

毫米波频段频率选择表面的分析计算

首先介绍了如何用辅助场量的FDTD方法分析计算毫米波波段的频率选择表面,然后给出了一种能快速计算多层FSS频率响应的方法——拟合电路法,并和FDTD计算的结果比较,结果吻合较好。     

An Effective Multigrid Preconditioned CG Algorithm for Millimeter Wave Scattering by an Infinite Plane Metallic Grating

An effective multigrid based preconditioned conjugate gradient method is developed to solve electromagnetic large matrix problem for millimeter wave scattering application. By using multigrid technique we restrict the large matrix equation to a relative smaller matrix and which can be solved rapidly. The solution is prolonged as the initial guess for the conjugate gradient (CG) method. Numerical results show that our developed method can reach five times improvement of computational complexity.     

Application of SSOR Preconditioning Technique to Method of Lines for Millimeter Wave Scattering

In this paper, symmetric successive overrelaxation (SSOR) preconditioned CG technique are introduced into method of lines (MOL) to further enhance the computational efficiency of this semi-analytic method. Millimeter wave scattering by an infinite plane metallic grating is used as the examples to describe its implementation, whose analysis usually needs fast algorithms because of electrically large dimension. For arbitrary incident wave, Helmholz equation and boundary condition are used to calculate the impedance matrix and then to obtain reduced current-voltage linear matrix equation in spatial domain. An effective symmetric successive overrelaxation preconditioned conjugate gradient iterative method, SSOR-PCG, is chosen to solve this matrix equation. With SSOR as the preconditioner as well as its efficient implementing in CG algorithm, PCG method can converge to accurate solution in much fewer iteration steps.     

An Efficient MAINV Preconditioned COCG Method for FEM Analysis of Millimeter Wave Filters

The modified AINV (MAINV) sparse approximate inverse preconditioner is applied to the conjugate orthogonal conjugate gradient (COCG) iterative method for solving a large systems of linear equations resulting from the use of edge finite element method (FEM). The proposed preconditioner is derived from basic AINV process by adding pivots compensation strategy to avoid the potential breakdowns. Numerical experiments on several typical millimeter wave structrues demonstrate the effectiveness of the MAINV-COCG method, in comparison with other conventional methods.     

Analysis of a Novel Metal Frequency Selective Surface of Millimeter Wave Comparator

In this paper, using s-parameter matrix method, novel structure for frequency selective surface is introduced and analysized to get its frequency character near the frequency of 94GHz. The results show that the novel structrues have the advantage of simple structure and small simension with wide bandwith.     

Application of Robust Incomplete Cholesky Factorizations Preconditioned CG Algorithms for FEM Analysis of Millimeter Wave Filters

The Incomplete Cholesky factorizations preconditioning scheme is applied to the conjugate gradient (CG) method for solving a large system of linear equations resulting from finite element method (FEM) analysis of millimeter wave filters. As is well known, the convergence of CG method deteriorates with increasing EM wave number and in millimeter wave band the eigen-values of A are more and more scattered between both the right and the left half-plane. The efficient implementation of this preconditioned CG (PCG) algorithm is described in details for Complex coefficient matrix. With incomplete factorization preconditioning scheme in the conjugate gradient algorithm, this PCG approach can reach convergence in 20 times CPU time shorter than CG for several typical millimeter wave structures.     

Effect of Dielectric Groove Profiles on Reflection Characteristics of Millimeter Wave Frequency Selective Surface

In this paper, the frequency selective reflection characteristics of dielectric periodic structures with arbitrary groove profiles are analyzed by a method which combines the multimode network theory with the rigorous mode matching procedure. Emphasis is placed on the discussion about the effect of the different groove profiles, such as rectangle, trapezoid, increasing cosine and triangle, on the reflection characteristics of the millimeter wave (MMW) frequency selective surface (FSS). Some useful guidelines for the design of the MMW dielectric FSS are thus suggested. Moreover, the physical explanation of the related wave phenomenon is given.     

Periodicity Perturbed Grounded Frequency Selective Surface Arrays as Millimeter Wave Random Phase Coherence Destroying Diffusers

This paper presents the design, construction and testing of perturbed periodicity slot type grounded Frequency Selective Surface (FSS) array as millimeter wave (mm-wave) random phase diffusers to eliminate speckle in active mm-wave imaging. To create a random phase diffuser for destroying the coherence of mm-wave sources we proposed FSS based diffusers arrays where the periodicities between the elements are different thought the slot of the cells are similar. The impacts of periodicity variations of both TM and TE field directions have been investigated. The periodicity of an FSS is the main design parameter used to optimize the phase shifting properties of the arrays. The critical parameters of the diffuser arrays design, such as phase relation with periodicity and optimum designed consideration are discussed. We designed the FSS arrays with Finite Integral Technique, fabricated by using etching technique and characterized the S-parameters with a free space Millimeter Wave Vector Network Analyzer (MVNA).     

Efficient Analysis of Millimeter Wave Circuit Using Numerical Calibration Technique

In this paper, A numerical technique, called short-open calibration (SOC), in conjunction with edge-based finite element method (FEM) is employed to analyze millimeter wave circuit that can be segmented into two distinct section: static model of feedlines and dynamic model of circuit discontinuity. The derivation of reflection coefficient of 3D discontinuities is arranged in two steps. In the first step, this SOC technique is incorporated into the FEM for mesh truncation of computaional domain. In this way, much faster convergence is achieved for large-sparse linear matrix equations from FEM by this termination than by perfectly matching layers (PML). The field distribution of the dominated mode in uniform feedlines and entire circuit is obtained individually by exciting a pair of even and odd impressed voltages along the struture. In step two, Scattering parameters based on the voltages and current defintion is calculated by integral of electric and magnetic fields. Numerical solutions for a class of planar circuit discontuities are very well compared with those published in the available literatures.     

Analysis of Frequency Selective Surfaces at Millimeter Wave Band Using the Hertz Vector Potential Method

In this work, the Hertz vector potential method was used to obtain the dyadic Green’s function components for frequency selective surfaces (FSS) on an anisotropic layer. The considered structures are composed by periodic arrays of conducting crossed dipole and rectangular patch elements. Results of reflected power were obtained by using the moment method. Curves for the reflected power versus frequency are presented as function of the structural parameters, assuming x, y, and z orientation for the optical axis in the anisotropic substrate.     

Analysis of Millimeter Wave Scattering by the Infinite Plane Metallic Grating Using PCG-FFT Technique

In this paper, both fast Fourier transformation (FFT) and preconditioned CG technique are introduced into method of lines (MOL) to further enhance the computational efficiency of this semi-analytic method. Electromagnetic wave scattering by an infinite plane metallic grating is used as the examples to describe its implementation. For arbitrary incident wave, Helmholz equation and boundary condition are first transformed into new ones so that the impedance matrix elements are calculated by FFT technique. As a result, this Topelitz impedance matrix only requires O(N) memory storage for the conjugate gradient FFT method to solve the current distribution with the computational complexity O(N log N) . Our numerical results show that circulate matrix preconditioner can speed up CG-FFT method to converge in much smaller CPU time than the banded matrix preconditioner.     

Frequency Selective Characteristics of Dielectric Periodic Structures for Millimeter Wave Application

In this paper, the frequency selective reflection characteristics of dielectric periodic structures for the oblique incidence of a plane wave are analyzed by a method which combines the multimode network theory with the rigorous mode matching method. The variations of the total reflection characteristics with the geometric dimensions of the dielectric periodic structures are systematically investigated to develop useful guidelines for the design of the dielectric frequency selective surface. Moreover, the relationship between the related wave phenomenon and the dispersion characteristics of multilayer plane dielectric structure is explained with the theory of plane dielectric waveguide.     

A Sensitivity Analysis of Frequency Selective Surfaces at Millimeter Wave Band

This work presents a sensitivity analysis for the resonant frequency and bandwidth of frequency selective surfaces (FSS) as a function of the structural parameters. The frequency selective surface structure considered here is composed by crossed dipole conductive patches deposited on an anisotropic dielectric layer. Firstly, the moment method is used in combination with the immittance technique in the spectral domain to determine the frequency response of the analyzed structure. Secondly, numerical techniques are used to obtain the resonant frequency and bandwidth sensitivities as a function of the considered FSS structural parameters.     

Analysis of Frequency Selective Surfaces with Metallic and Dielectric Losses at Millimeter Wave Range

In this paper, a theoretical analysis of scattering from a doubly frequency selective surfaces (FSS) with dielectric and metallic losses in the millimeter wave range is presented. The theoretical analysis involves the solution of the electric field integral equation relating the induced current in the FSS in the presence of anisotropic dielectric layers. The method of moment is employed to obtain numerical results. The frequency selective surface structure considered is composed by conducting patch elements sandwiched between two anisotropic dielectric layers. Three different anisotropic materials are considered: Epsilam-10, Alumina, and Sapphire. The sapphire presents low losses when compared with the other two dielectric materials. The most common metals, as copper and aluminum, are considered in this analysis. None significant metallic losses were observed for any considered metal. Numerical results are presented for the scattering characteristics and for dielectric and metallic losses parameters.     

Linear Interference Cancellation of Asynchronous CDMA Systems by Preconditioned CG Method

It is well known that the iterative method is used for solving a set of linear equations corresponding to linear interference cancellation structures. An ideal computation of the decorrelating or the linear minimum mean-squared-error (LMMSE) detector requires order K ³ flops, where K is the number of users. To alleviate the computational complexity, iterative decorrelating and the LMMSE detectors are proposed. In this paper, the symmetric successive over relaxation (SSOR) preconditioning scheme is applied to the conjugate gradient (CG) method. The performance of the detectors is investigated and it is found that the SSOR preconditioned CG (PCG) method can provide significantly faster convergence than CG method.     

三维随机粗糙海面与舰船的复合电磁特性的高频方法分析研究

3维随机粗糙海面与其上方复杂目标复合电磁(EM)散射特性的建模与分析在微波遥感、目标识别、雷达成像、导弹制导等领域中有着重要的研究价值。该文主要研究了基于高频算法的随机粗糙海面及舰船的复合电磁散射特性,开发了PO-IPO混合方法,为3维随机粗糙海面与复杂目标一体化高效求解提供了新思路。文中分别使用了物理光学方法(PO)、迭代物理光学方法(IPO)、PO-PO以及PO-IPO混合方法对海面及舰船进行了建模与仿真,其中,引入锥形波来代替平面波作为发射源,锥形波可以更好地抑制粗糙面在边缘位置被突然截断而形成的电磁反射和边缘绕射等效应。从数值仿真结果中可以看出,PO-IPO混合方法可将复杂物体本身面元间以及粗糙海面与物体间的耦合作用考虑在内,因此PO-IPO可以作为一种有效的途径来快速获取随机粗糙海面及舰船的复合电磁散射特性。      

A Tri-Band Frequency Selective Surface (FSS) to Diplex Widely Separated Bands for Millimeter Wave Remote Sensing

A substrate-backed frequency selective surface (FSS) is presented for diplexing the widely separated frequency spectrum centered at 55, 89, and 183 GHz with varying bandwidth for spatial separation in the quasi-optical feed network of the millimeter wave sounder. A unit cell composed of a crossed dipole integrated with a circular ring and loaded inside a square ring is optimized for tri-band frequency response with transmission window at 89 GHz and rejection windows at 55 and 183 GHz. The reflection and transmission losses predicted for the optimized unit cell (728 μm?×?728 μm) composed of dissimilar resonant shapes is less than 0.5 dB for transverse electric (TE) and transverse magnetic (TM) polarizations and wide angle of incidence (0°–45°). The FSS is fabricated on a 175-μm-thick quartz substrate using microfabrication techniques. The transmission characteristics measured with continuous wave (CW) terahertz transmit receive system are in good agreement with the numerical simulations.     

Simulation of Millimeter Wave Circulators by FEM with Unifrontal/Multifrontal Technique

The combination of unifrontal and multifrontal techniques is applied for solving a large, sparse, and unsymmetric system of linear equations resulting from the use of edge-based finite element method (FEM) for millimeter wave ferrite devices. The formulation of finite element method combined with the perfectly matched layers (PML) is given and the combined algorithm of unifrontal and multifrontal methods is described. The lower data movement of unifrontal method and the lower fill-in of normal multifrontal methods are combined for an algorithm with their features. The performance of typical waveguide junction circulators is analyzed and the calculated results are compared with those obtained from the literature.