Levent Sevgi

Numerical computations of different diffraction representations for the canonical wedge-scattering problem are discussed. Representations include total-field exact series summation, exact diffraction integral, and the Physical Optics (PO), Physical Theory of Diffraction (PTD), and Parabolic Equation (PE) techniques, and the Uniform Theory of Diffraction (UTD). Numerical challenges and advantages of each are given.

This paper aims to provide a tutorial on the visualization of complex functions. The MATLAB-based package ComplexGUI was prepared to illustrate mappings by elementary complex functions. The tool shows how user-defi ned curves and regions are transformed by some elementary functions. Concepts such as branch points, branch cuts, the principal branch of multivalued functions, and Riemann surfaces are emphasized. The package also enables asymptotic evaluation of Bessel integrals along user-specifi ed contours, and compares the result with the built-in function in MATLAB. The tool allows deforming the integration contour to a path through the saddle points in the direction of the steepest-decent path to obtain a better result.

A MATLAB-based virtual diffraction tool, using analytical exact as well as well-known high-frequency asymptotic (HFA) techniques, is introduced. Electromagnetic wave scattering from a wedge-shaped object with perfect electrical conductor (PEC) boundaries, under both line-source and plane-wave illuminations, can be automatically analyzed. Effects of various parameters on the reflection, refraction, and diffraction can be investigated. Comparisons among Geometrical Optics (GO), Uniform Theory of Diffraction (UTD), Physical Optics (PO), Physical Theory of Diffraction (PTD), and Parabolic Equation (PE) models are possible through many scenarios and illustrations.

Propagation modeling and simulation approaches for the use of High Frequency Surface Wave Radar (HFSWR) are discussed. HFSWR uses vertically polarized surface waves along multi-mixed paths in the lower HF band (3 MHz - 15 MHz). Various numerical propagators are reviewed with an early analytical model. Split Step Fast Fourier Transformation, finite- difference, and finite-element solutions of the well-known one-way, forward propagation Parabolic Equation (PE) model are presented. MATLAB-based numerical propagation prediction tools based on these models are listed. Tests and comparisons among these analytical and numerical tools are given for some canonical surface wave propagation scenarios. The Millington effect for both smooth and irregular terrain paths, which contain land-sea and sea-land transitions, is also discussed.

Realistic high frequency surface wave radar (HFSWR) targets are investigated numerically in terms of electromagnetic wave -- target interactions. Radar cross sections (RCS) of these targets are simulated via both the finite-difference time-domain (FDTD) method and the Method of Moments (MoM). The virtual RCS prediction tool that was introduced in previous work is used for these investigations. The virtual tool automatically creates the discrete FDTD model of the target under investigation and performs the FDTD RCS analysis. It also automatically constructs a MoM wire grid model of the target; therefore, it is also possible to compare FDTD results against the MoM-based NEC (Numerical Electromagnetic Code) data. Bi-static RCS patterns under a variety of illuminations over the whole HF band (3-30 MHz) are presented. The mono-static RCS vs. frequency of these targets is also given.

Surface Wave High Frequency Radars (SWHFR) are taken into account in the content of modeling and simulation challenges. Examples related to multi-mixed path surface wave propagation, radar cross section (RCS) prediction, and total radar echo showing target, clutter, noise, and interference are presented.

A novel FDTD-based virtual electromagnetic compatibility tool for the prediction of electromagnetic emissions from a multilayer printed circuit board is introduced. Tests are performed with characteristic structures and sample simulation results are presented.

Education and training problems and challenges in EMC Engineering are discussed. The necessity of physics-based modeling (theory) and hands-on training (practice) are emphasized. An introductory level EMC lecture and a short course outline are given for modern EMC education.

A novel FDTD-based virtual radar cross section (RCS) prediction tool is introduced. Characteristic examples using simple three-dimensional structures, as well as more-realistic complex air and surface targets, are presented. The virtual tool automatically constructs a wire-grid model of the structure under investigation. It is therefore also possible to compare FDTD results against MoM-based NEC (Numerical Electromagnetics Code) data. It is shown that this virtual tool can be used for both educational and research purposes.

Floquet wave and element-by-element summation representations are implemented to investigate the radiation from a periodic, rectangular array of linearly phased/sequentially pulsed dipoles in the frequency- and time-domains. A synthetic aperture type formulation for Floquet wave representation and an asymptotic formulation for the element-by-element summation representation are developed. Numerical results are presented to demonstrate the efficiency of the Floquet wave representation in terms of radiating, non-radiating and diffracted wave constituents and then validated via comparison with direct summation over the contributions of individual dipole radiations.