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28
Patch Antennas on Ferromagnetic Substrates
"... Abstract—Patch antennas on ferrite substrates allow for pattern control, frequency shifting, and scattering reduction. This is achieved by external magnetic field biasing coupled with the inherent magnetization of the ferrite substrate. Measurements and analytical studies based on the method of mome ..."
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Abstract—Patch antennas on ferrite substrates allow for pattern control, frequency shifting, and scattering reduction. This is achieved by external magnetic field biasing coupled with the inherent magnetization of the ferrite substrate. Measurements and analytical studies based on the method of moments (MoM) have verified these attractive properties of ferrite substrates. However, verification of the analysis is difficult and, furthermore, previous models have relied on uniform biasing across the substrate. In this paper, we present a hybrid finite elementboundary integral (FEBI) method, which permits modeling of the true nonuniform bias fields within the substrate for a more accurate prediction of the ferrite patch performance. After validation of the proposed simulation and a demonstration of the inherent properties of the ferrite patch, it is shown that nonuniform biasing is responsible for additional frequency shifts. We also identify the poor condition of the resulting matrix systems and relate this situation to the predictable occurrence of nonpropagating substrate modes. A more robust iterative solver with preconditioning is, therefore, proposed and applied to handle these situations. Index Terms — Anisotropic media, antennas, antenna theory, ferrites, finiteelement methods, microstrip antennas.
Analysis of direct and inverse cavity scattering problems
 Numer. Math. Theor. Meth. Appl
"... Abstract. Consider the scattering of a timeharmonic electromagnetic plane wave by an arbitrarily shaped and filled cavity embedded in a perfect electrically conducting infinite ground plane. A method of symmetric coupling of finite element and boundary integral equations is presented for the soluti ..."
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Abstract. Consider the scattering of a timeharmonic electromagnetic plane wave by an arbitrarily shaped and filled cavity embedded in a perfect electrically conducting infinite ground plane. A method of symmetric coupling of finite element and boundary integral equations is presented for the solutions of electromagnetic scattering in both transverse electric and magnetic polarization cases. Given the incident field, the direct problem is to determine the field distribution from the known shape of the cavity; while the inverse problem is to determine the shape of the cavity from the measurement of the field on an artificial boundary enclosing the cavity. In this paper, both the direct and inverse scattering problems are discussed based on a symmetric coupling method. Variational formulations for the direct scattering problem are presented, existence and uniqueness of weak solutions are studied, and the domain derivatives of the field with respect to the cavity shape are derived. Uniqueness and local stability results are established in terms of the inverse problem. AMS subject classifications: 78A46, 78M30 Key words: electromagnetic cavity, direct problem, inverse problem, finite element methods,
Anomalous properties of scattering from cavities partially loaded with doublenegative or singlenegative metamaterials
 Progress In Electromagnetics Research, PIER
, 2005
"... Abstract—In this paper, the theoretical justification and the numerical verification of the anomalous scattering from cavities partially filled with metamaterials are presented. A hybrid numerical formulation based on the Finite Element Method (FEM) and on the Boundary Integral (BI) for the analysis ..."
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Abstract—In this paper, the theoretical justification and the numerical verification of the anomalous scattering from cavities partially filled with metamaterials are presented. A hybrid numerical formulation based on the Finite Element Method (FEM) and on the Boundary Integral (BI) for the analysis of cavity backed structures with complex loading metamaterials is first presented. The proposed approach allows the analysis of cavities filled with materials described by tensorial linear constitutive relations, which may well describe artificial metamaterials synthesized with proper inclusions in a host dielectric. It is found that cavities loaded with pairs of metamaterial layers with “resonant ” features possess unusual scattering properties, and with judicious selection of constitutive parameters for these materials the transparency effect or significant enhancement in the backscattering from such cavities are obtained. This may be considered
Radiation Characteristic of Cavity Backed Aperture Antennas in Finite Ground Plane Using the Hybrid FEM/MoM Technique and Geometrical Theory of Diffraction
, 1996
"... : A technique using hybrid Finite Element Method (FEM)/Method of Moments (MoM), and Geometrical Theory of Diffraction (GTD) is presented to analyze the radiation characteristics of cavity fed aperture antennas in a finite ground plane. The cavity which excites the aperture is assumed to be fed by a ..."
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: A technique using hybrid Finite Element Method (FEM)/Method of Moments (MoM), and Geometrical Theory of Diffraction (GTD) is presented to analyze the radiation characteristics of cavity fed aperture antennas in a finite ground plane. The cavity which excites the aperture is assumed to be fed by a cylindrical transmission line. The electromagnetic (EM) fields inside the cavity are obtained using FEM. The EM fields and their normal derivatives required for FEM solution are obtained using (1) the modal expansion in the feed region and (2) the MoM for the radiating aperture region(assuming an infinite ground plane). The finiteness of the ground plane is taken into account using GTD. The input admittance of open ended circular, rectangular, and coaxial line radiating into free space through an infinite ground plane are computed and compared with earlier published results. Radiation characteristics of a coaxial cavity fed circular aperture in a finite rectangular ground plane are verified ...
A novel preconditioning technique and comparison of three formulations for the hybrid FEM/MoM method
 Appl. Computat. Electromagn. Soc. (ACES) J
, 2000
"... Abstract – Hybrid FEM/MoM methods combine the finite element method (FEM) and the method of moments (MoM) to model inhomogeneous unbounded problems. These two methods are coupled by enforcing field continuity on the boundary that separates the FEM and MoM regions. There are three ways of formulating ..."
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Abstract – Hybrid FEM/MoM methods combine the finite element method (FEM) and the method of moments (MoM) to model inhomogeneous unbounded problems. These two methods are coupled by enforcing field continuity on the boundary that separates the FEM and MoM regions. There are three ways of formulating hybrid FEM/MoM methods: outwardlooking formulations, inwardlooking formulations and combined formulations. In this paper, the three formulations are compared in terms of computerresource requirements and stability for four sample problem geometries. A novel preconditioning technique is developed for the outwardlooking formulation. This technique greatly improves the convergence rate of iterative solvers for the types of problems investigated in this study. Index Terms: FEM, MoM, EMC, sparse matrix, permutation, preconditioning, iterative solvers.
Electromagnetic Scattering by Multiple Cavities Embedded in the Infinite 2D Ground Plane
"... Abstract ─ This paper is concerned with the mathematical analysis and numerical computation of the electromagnetic wave scattering by multiple open cavities, which are embedded in an infinite twodimensional ground plane. By introducing a new transparent boundary condition on the cavity apertures, t ..."
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Abstract ─ This paper is concerned with the mathematical analysis and numerical computation of the electromagnetic wave scattering by multiple open cavities, which are embedded in an infinite twodimensional ground plane. By introducing a new transparent boundary condition on the cavity apertures, the scattering problem is reduced to a boundary value problem on the twodimensional Helmholtz equation imposed in the separated interior domains of the cavities. The existence and uniqueness of the weak solution for the model problem is studied by using a variational approach. A block GaussSeidel iterative method is introduced to solve the coupled system. Numerical examples are presented to show the efficiency and accuracy of the proposed method.
Analysis of ThreeDimensionalCavityBacked Aperture Antennas Using a Combined Finite . . .
, 1995
"... A combined finite element method (FEM) and method of moments (MoM) technique is presented to analyze the radiation characteristics of a cavityfed aperture in three dimensions. Generalized feed modeling has been done using the modal expansion of fields in the feed structure. Numerical results for so ..."
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A combined finite element method (FEM) and method of moments (MoM) technique is presented to analyze the radiation characteristics of a cavityfed aperture in three dimensions. Generalized feed modeling has been done using the modal expansion of fields in the feed structure. Numerical results for some feeding structures such as a rectangular waveguide, circular waveguide, and coaxial line are presented. The method also uses the geometrical theory of diffraction (GTD) to predict the effect of a finite ground plane on radiation characteristics. Input admittance calculations for open radiating structures such as a rectangular waveguide, a circular waveguide, and a coaxial line are presented. Numerical data for a coaxialfed cavity with finite ground plane are verified with experimental data. 1. Introduction Cavitybacked aperture antennas are very popular in aerospace applications because of their conformal nature. The cavities can also have various types of microstrip antennas residing...
ANALYSIS OF TRANSIENT ELECTROMAGENTIC SCATTERING FROM A THREEDIMENSIONAL OPEN CAVITY∗
"... Abstract. This paper is concerned with the mathematical analysis of the timedomain Maxwell equations in a threedimensional open cavity. An exact transparent boundary condition is developed to reformulate the open cavity scattering problem in an unbounded domain, equivalently, into an initialbound ..."
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Abstract. This paper is concerned with the mathematical analysis of the timedomain Maxwell equations in a threedimensional open cavity. An exact transparent boundary condition is developed to reformulate the open cavity scattering problem in an unbounded domain, equivalently, into an initialboundary value problem in a bounded domain. The wellposedness and stability are studied for the reduced problem. Moreover, an a priori estimate is established for the electric field with a minimum regularity requirement for the data.
Radiation of a Coaxial Line Into a HalfSpace
"... Abstract—We present a new approach to the problem of radiation by a coaxial line into a halfspace. We obtain boundaryintegral equations for the current densities over the walls of the coax and its opening to the halfspace. Using the modes of the coax for basis and testing functions, we convert th ..."
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Abstract—We present a new approach to the problem of radiation by a coaxial line into a halfspace. We obtain boundaryintegral equations for the current densities over the walls of the coax and its opening to the halfspace. Using the modes of the coax for basis and testing functions, we convert the integral equations to an infinite system of linear equations, the unknowns being the coefficients of the current density expansions. We demonstrate how, by solving a small subsystem, we can obtain the fields everywhere in space. Index Terms—Boundaryintegral equations (BIEs), coaxialline radiation, method of moments (MoM), modal basis functions, modal testing functions. W I.
Frequency Response Calculations of Input Characteristics of CavityBacked Aperture Antennas Using AWE With Hybrid FEM/MoM Technique
, 1997
"... 2 List of Symbols 3 1.0 Introduction 5 2.0 Hybrid FEM/MoM Technique 7 3.0 AWE Implementation 11 4.0 Numerical Results 12 5.0 Concluding Remarks 16 Acknowledgments 17 Appendix 18 References 2 Abstract Application of Asymptotic Waveform Evaluation (AWE) is presented in conjunction with a hybrid Fin ..."
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2 List of Symbols 3 1.0 Introduction 5 2.0 Hybrid FEM/MoM Technique 7 3.0 AWE Implementation 11 4.0 Numerical Results 12 5.0 Concluding Remarks 16 Acknowledgments 17 Appendix 18 References 2 Abstract Application of Asymptotic Waveform Evaluation (AWE) is presented in conjunction with a hybrid Finite Element Method (FEM) / Method of Moments (MoM) technique to calculate the input characteristics of cavitybacked aperture antennas over a frequency range. The hybrid FEM/ MoM technique is used to form an integropartialdifferential equation to compute the electric field distribution of the cavitybacked aperture antenna. The electric field, thus obtained, is expanded in a Taylor series around the frequency of interest. The coefficients of Taylor series (called "moments") are obtained using the frequency derivatives of the integropartialdifferential equation formed by the hybrid FEM/MoM technique. Using the moments the electric field in the cavity is obtained over a frequency range. U...