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Title: THE NUMERICAL OF CHARACTERISTICS FOR ELECTROMAGNETICS
Abstract: The objective of this study is to explore the benefits of using the theory of characteristics to develop accurate and efficient numerical algorithms for Computational Electromagnetics. The present work adapts the numerical method of Characterisitics (MOC) from Computational Fluid Dynamics to the one-dimensional Maxwell curl equations in the time domain. The relevant theory of characterisitics is developed and the inverse matching method is used to develop two numerical algorithms based on different interpolation schemes in the initial data surface. Stability and dispersion for these algorithms are discussed. Results are given for one-dimensional model problems involving free space pulse propagation, scattering from perfect conductors and reflection/transmission for lossy dielectric materials. The model problems are designed to provide quantitative insight to both accuracy and efficiency for different classes of realistic application problems. The Finite-Difference Time-Domain (FDTD) method is used as a convenient reference algorithm for comparison. It is demonstrated that these algorithms have accuracy comparable to FDTD, but do not require staggered grid storage, which simplifies impedance boundary conditions and implementation on nonuniform grids. The thoery of characteristics demonstrates a very natural outer boundary condition without nonreflecting approximations or matched layers. A dispersion enhanced version of the MOC is also developed which has phase errors 50-5000 times lower than FDTD. This approach appears promising for development of dispersion enhanced characteristic based schemes for two and three dimensional applications.
Author(s): J.H. Beggs, D.L. Marcum, S-L. Chan
File Type: Journal Paper
Issue:Volume: 14      Number: 2      Year: 1999
Download Link:Click here to download PDF     File Size: 962 KB

Title: VOLUME LOADING -- A NEW PRICIPLE FOR SMALL ANTENNAS
Abstract: Volume loading means placing conductively enclosed volumes at the ends of the arms of a short linear antenna to increase and control the capacitance of the structure. This technique allows tuning the antenna to make it series-resonant at a design frequency for which it is electrically small. This paper describes the discovery and development of the concept, gives some computed examples to illustrate the relation between shape and performance, and describes some experimental work, including a 900 MHx corless phone demonstration design.
Author(s): D.B. Miron
File Type: Journal Paper
Issue:Volume: 14      Number: 2      Year: 1999
Download Link:Click here to download PDF     File Size: 662 KB

Title: SHAPED REFLECTOR ANTENNA ANALYSIS BY GRAPHICAL PROCESSING METHODS
Abstract: This paper presents the application of GRECO code to obtain the radiation pattern of single reflector antennas. Shaped reflectors with arbitrary geometries are modelled by CAD software. The GRECO graphical processing technique [3][4] [5] is used in order to extract the relevant geometrical information from the CAD geometry database. Surface reflection and edge diffraction are respectively analyzed by Physical Optics approximation and Equivalent Edge Currents Method.
Author(s): J.M. Rius, M. Vall-Ilossera, C. Salazar, A. Cardama
File Type: Journal Paper
Issue:Volume: 14      Number: 2      Year: 1999
Download Link:Click here to download PDF     File Size: 534 KB

Title: VALIDATION AND DEMONSTRATION OF FREQUENCY APPROXIMATION METHODS FOR MODELING DISPERSIVE MEDIA IN FDTD
Abstract: Recently, digital signal processing techniques were used to design, analyze and implement discrete models of polarization dispersion for the Finite-Difference Time-Domain (FDTD) method. The goals of the present work are to illustrate the FDTD update equations for these techniques and to validate and demonstrate these techniques for one-dimensional problems involving reflections from dispersive dielectric half-spaces. Numerical results are compared with several other dispersive medial FDTD implementations.
Author(s): J.H. Beggs
File Type: Journal Paper
Issue:Volume: 14      Number: 2      Year: 1999
Download Link:Click here to download PDF     File Size: 484 KB

Title: SCATTERING FROM A PERFECT CONDUCTOR CYLINDER WITH AN INHOMOGENEOUS COATING THICKNESS OF GYROELECTRIC CHIRAL MEDIUM: EXTENDED MODE MATCHING METHOD
Abstract: Based on the eigenfunction expansion of electromagnetic waves in the gyroelectric chiral medium, an extended mode-matching method is developed to study the electromagnetic scattering of a perfect electric conductor (PEC) circular cylinder with an inhomogeneous coating thickness of gyroelectric chiral medium. Excellent convergence property of the bistatic echo width is numerically verified, which establishes the reliability and applicability of the present extended mode-matching method for two-dimensional problem of gyroelectric chrial medium.
Author(s): D. Cheng, Y.M.M. Antar
File Type: Journal Paper
Issue:Volume: 14      Number: 2      Year: 1999
Download Link:Click here to download PDF     File Size: 540 KB

Title: IMPROVED MODELING OF SHARP ZONES IN RESONANT PROBLEMS WITH THE TLM METHOD
Abstract: Several new modified nodes based on the symmetrical condensed node with stubs are proposed to solve the difficulty of the TLM method in modeling problems highly dependent on frequency. These nodes avoid the problem of indirect modeling at critical points, such as bends and corners, thus providing more accurate results and flexibility in the modeling of conducting parts. The new nodes are applied to specific problems of rectangular waveguides loaded with rectangular irises of finite width to verify their capability to predict resonant phenomena.
Author(s): J. A. Morente, J.A. Porti, H. Magan, O. Torres
File Type: Journal Paper
Issue:Volume: 14      Number: 2      Year: 1999
Download Link:Click here to download PDF     File Size: 413 KB