Kostyantyn Sirenko

An FFT-Accelerated FDTD Scheme with Exact Absorbing Conditions for Characterizing Axially Symmetric Resonant Structures

An accurate and e-cient flnite-difierence time-domain (FDTD) method for characterizing transient waves interactions on axially symmetric structures is presented. The method achieves its accuracy and e-ciency by employing localized and/or fast Fourier transform (FFT) accelerated exact absorbing conditions (EACs). The paper details the derivation of the EACs, discusses their implementation and discretization in an FDTD method, and proposes utilization of a blocked-FFT based algorithm for accelerating the computation of temporal convolutions present in nonlocal EACs. The proposed method allows transient analyses to be carried for long time intervals without any loss of accuracy and provides reliable numerical data pertinent to physical processes under resonant conditions. This renders the method highly useful in characterization of high-Q microwave radiators and energy compressors. Numerical results that demonstrate the accuracy and e-ciency of the method are presented.

An Efficient Discontinuous Galerkin Finite Element Method for Highly Accurate Solution of Maxwell Equations

A discontinuous Galerkin finite element method (DG-FEM) with a highly accurate time integration scheme for solving Maxwell equations is presented. The new time integration scheme is in the form of traditional predictor-corrector algorithms, PE(CE)m, but it uses coefficients that are obtained using a numerical scheme with fully controllable accuracy. Numerical results demonstrate that the proposed DG-FEM uses larger time steps than DG-FEM with classical PE(CE)m schemes when high accuracy, which could be obtained using high-order spatial discretization, is required.

Incorporation of Exact Boundary Conditions into a Discontinuous Galerkin Finite Element Method for Accurately Solving 2D Time-Dependent Maxwell Equations

A scheme that discretizes exact absorbing boundary conditions (EACs) to incorporate them into a time-domain discontinuous Galerkin finite element method (TD-DG-FEM) is described. The proposed TD-DG-FEM with EACs is used for accurately characterizing transient electromagnetic wave interactions on two-dimensional waveguides. Numerical results demonstrate the proposed methods superiority over the TD-DG-FEM that employs approximate boundary conditions and perfectly matched layers. Additionally, it is shown that the proposed method can produce the solution with ten-eleven digit accuracy when high-order spatial basis functions are used to discretize the Maxwell equations as well as the EACs.

COMPRESSION AND RADIATION OF HIGH-POWER SHORT RF PULSES. II. A NOVEL ANTENNA ARRAY DESIGN WITH COMBINED COMPRESSOR/RADIATOR ELEMENTS

The paper discusses the radiation of compressed high power short RF pulses using two difierent types of antennas: (i) A simple monopole antenna and (ii) a novel array design, where each of the elements is constructed by combining a compressor and a radiator. The studies on the monopole antenna demonstrate the possibility of a high power short RF pulses e-cient radiation even using simple antennas. The studies on the novel array design demonstrate that a reduced size array with lower pulse distortion and power decay can be constructed by assembling the array from elements each of which integrates a compressor and a radiator. This design idea can be used with any type of antenna array; in this work it is applied to a phased array.

Modeling and analysis of transients in periodic gratings. II. Resonant wave scattering

In this paper we represent a number of new physical results obtained using time domain methods and based on equivalent replacement of initially open electrodynamic problems with closed ones. These results prove the high efficiency and reliability of the approach, being grounded in our companion paper in this issue.

COMPRESSION AND RADIATION OF HIGH-POWER SHORT RF PULSES. I. ENERGY ACCUMULATION IN DIRECT-FLOW WAVEGUIDE COMPRESSORS

Proper design of e-cient microwave energy compressors requires precise understanding of the physics pertinent to energy accumulation and exhaust processes in resonant waveguide cavities. In this paper, practically for the flrst time these highly non-monotonic transient processes are studied in detail using a rigorous time-domain approach. Additionally, in∞uence of the geometrical design and excitation parameters on the compressors performance is quantifled in detail.

A convergence analysis for a sweeping preconditioner for block tridiagonal systems of linear equations

Summary We study sweeping preconditioners for symmetric and positive definite block tridiagonal systems of linear equations. The algorithm provides an approximate inverse that can be used directly or in a preconditioned iterative scheme. These algorithms are based on replacing the Schur complements appearing in a block Gaussian elimination direct solve by hierarchical matrix approximations with reduced off-diagonal ranks. This involves developing low rank hierarchical approximations to inverses. We first provide a convergence analysis for the algorithm for reduced rank hierarchical inverse approximation. These results are then used to prove convergence and preconditioning estimates for the resulting sweeping preconditioner. Copyright

Slot resonances in axially-symmetrical radiators of pulsed and monochromatic TM 0n - waves

Slot resonances on TEM -waves in narrow radial and circular coaxial waveguides have been studied. These resonances allow us to change significantly and to control efficiently the electrodynamic characteristics of axially-symmetrical radiators of pulsed and monochromatic TM0n - waves.

Diffraction Radiation Effects: A theoretical and experimental study.

This article is devoted to the theoretical and experimental study of diffraction radiation effects. Diffraction radiation is generated by the scattering of an eigenfield of density-modulated electron beam or a surface eigenwave of open dielectric waveguide on a nearby periodic structure. For the first time, these effects were studied using rigorous models exploiting exact absorbing conditions (EACs). This article also details the design and experimental testing of radiating elements for planar diffraction antennas with extremely low sidelobe levels, which exploit diffraction radiation effects.

An FDTD method with FFT-accelerated exact absorbing boundary conditions

An accurate and efficient finite-difference time-domain (FDTD) method for analyzing axially symmetric structures is presented. The method achieves its accuracy and efficiency using exact absorbing conditions (EACs) for terminating the computation domain and a blocked-FFT based scheme for accelerating the computation of the temporal convolutions present in non-local EACs. The method is shown to be especially useful in characterization of long-duration resonant wave interactions.