Gokhan Apaydin

• PhD
• Professor at Üsküdar University

This book introduces you to the world of electromagnetic waves. It contains a detailed analysis of electromagnetic surface waves in microwave absorbing layers. The surface waves play an important role in the complex scattering and absorption process. Although microwave absorbing coatings have been widely used since the Second World War, their prope...

Fresnel diffraction is a fundamental wave phenomenon happening near the shadow boundary behind a large opaque object. Previously, it was studied for the case of diffraction at large apertures in a black screen. In this paper, we investigate this phenomenon for perfectly conducting cylinders with large cross-sections. First, this theory is developed...

Fresnel diffraction is a fundamental wave phenomenon. This article explains its physical nature using the examples of the diffraction of acoustic waves at soft and hard half-planes and at large apertures on a black screen. It is shown that the shadow radiation by opaque screens plays a central role in these diffraction phenomena. Fresnel–Kirchhoff...

The physical theory of diffraction (PTD) is presented for triangular cylinders with faces consisting of soft (electric) and hard (magnetic) sections. It is shown that the specular reflections from such cylinders can be canceled and shifted with appropriate combinations of the soft and hard sections. The residual scattered field in the specular dire...

This exciting new resource presents a comprehensive introduction to the fundamentals of diffraction of two-dimensional canonical structures, including wedge, strip, and triangular cylinder with different boundary conditions. Maxwell equations are discussed, along with wave equation and scattered, diffracted and fringe fields. Geometric optics, as w...

A new version of PETOOL (Parabolic Equation Toolbox) is introduced with various additional capabilities. PETOOL is an open-source and MATLAB-based software tool with a user-friendly graphical user interface (GUI) for the analysis and visualization of electromagnetic wave propagation over variable terrain and through arbitrary atmosphere. Four novel...

Diffraction at a strip with one face soft (electric) and the other hard (magnetic) is studied. New results obtained by the method of moments (MoM) are compared with the asymptotic theory of edge diffraction (TED) for the totally soft and hard strips. Attention is given to diffraction of oblique incident waves including the grazing diffraction. Nove...

This study aims to visualize the diffraction effects of objects with rounded edges using method of moments (MoM). The comparison of scattering effects of wedges and trilateral cylinders are shown with and without rounded edges using fringe integral equations with physical theory of diffraction (PTD).

In this paper, we analyze equal width wave equation using multi-quadric quasi-interpolation (MQQI) scheme. The traveling wave solutions called solitary waves: Single solitary wave motion, interaction of two and three solitary waves and evolution of solitons have been investigated computationally. Several comparisons are made to demonstrate the effe...

The paper explores diffraction of acoustic waves at a two-dimensional hard trilateral cylinder with rounded edges. It represents the extension of the physical theory of diffraction (PTD) for finite objects with rounded edges. A first-order PTD approximation is developed. Integral equations are formulated for acoustic fringe waves and solved by meth...

Modified theory of physical optics (MTPO) solution for a soft/hard strip is analyzed. It is shown that this solution is incorrect because the MTPO Green function does not satisfy boundary conditions. Defects of MTPO in calculations of fringe waves are also noticed.

The paper investigates diffraction at trilateral cylinders with combinations of soft (electric) and hard (magnetic) faces. Scattered field in far zone is calculated according to the physical theory of diffraction. The first-order high-frequency approximation is constructed as a sum of single-diffracted edge waves. Plotted numerical data clearly dem...

An important contribution to the literature that introduces powerful new methods for modeling and simulating radio wave propagation A thorough understanding of electromagnetic wave propagation is fundamental to the development of sophisticated communication and detection technologies. The powerful numerical methods described in this book represent...

A MATLAB-based propagation tool called plate graphical user interface (PlateGUI), which calculates and shows electromagnetic (EM) fields inside a parallel-plate waveguide using different analytical and numerical models, was developed and is discussed in this article. PlateGUI can be used in graduate-level courses that deal with guided-wave theory a...

This chapter introduces a novel software tool (PETOOL), which is developed in MATLAB with graphical user interface (GUI) for the analysis and visualization of radio wave propagation through the homogeneous and inhomogeneous atmosphere, by incorporating variable terrain effects with the aid of the two-way split-step algorithm employing wide-angle pr...

This chapter explains how irregular terrain modeling can be implemented in the PE via several different mathematical approaches. The staircase approximation of the range dependent terrain profile is the best and easiest in order to handle DBC since neither analytical terrain function nor slope values are required. It emphasizes only on the requirem...

This chapter discusses the growth of mobile communication systems in recent years necessitates realistic 3D propagation modeling in urban regions as well as in tunnels. The PE method has also been used for this purpose. The 3D calibration of various PE models or codes is therefore essential before their applications in complex realistic environment...

This chapter discusses how the simplest propagation scenario used in analytical modeling is the flat Earth with PEC surface under line-source excitation. On the single knife edge problem, the ray summation approach is based on the construction of four different rays, related reflection, and diffraction coefficients using Fresnel integral. The param...

This chapter reviews fundamental EM-MODSIM concepts and the widely used numerical (PE and MoM) models through are liable VV&C procedure. The philosophy is to keep it as simple as possible so that it can be used as a basic computational electromagnetics note and to supply simple MATLAB codes so that, even beginners can use them. One of the most simp...

This chapter discusses how the groundwave propagation problem over a non-smooth spherical Earth with an impedance BC and a radially dependent atmosphere, excited by a vertical electric dipole located near the Earth's surface, requires the solution of a 3D EM wave equation in spherical coordinate. A novel FEMPE-based software tool (FEMIX) is introdu...

This chapter describes numerical propagation tools that calculate the ground wave path loss (PL) between any two points marked on their digital maps. This necessitates the solution of the EM wave equation in three dimensions in a manner that takes into account various EM effects, such as, the irregular terrain profile, the vegetation, the Earth's c...

This chapter discusses how powerful time-domain models are based on both the FDTD and the TLM methods. Analytical models are mostly based on mode and ray summations and require eigen-mode and eigen-ray extraction. Modes are global wave objects in guiding environments and can be used in representing any kind of excitation. They are confined transver...

This chapter discusses how the standard PE method is a one-way, forward propagation model, because of ignoring the backward propagation term. The standard PE model cannot reflect the effect of the interaction between the forward and backward waves, especially if there are valleys or hills with steep slopes along the propagation path. Both forward a...

The paper examines diffraction at rounded wedges with perfectly conducting faces. This topic was a subject of many publications which investigated mainly the total diffracted waves. In the present paper, we calculate specifically their fringe components to illustrate their sensitivity to the edge curvature. Such fringe waves provide substantial con...

A novel method is introduced for calculating fringe currents and fringe waves around the tip of a perfectly reflecting wedge under line source illumination. The time-domain fringe (non-uniform) currents are extracted with the finite-difference time-domain (FDTD) method. These currents are then fed into a free-space FDTD and fringe waves are excited...

A fast far-field approximation (FAFFA), which is simple to use, is applied to groundwave propagation modeling from a nonpenetrable surface with both soft and hard boundaries. The results are validated against available reference models as well as compared to other numerical methods such as split step parabolic equation model and the method of momen...

Diffraction by a strip with one face soft and the other face hard boundary condition is modeled numerically using finite-difference time-domain method, and the results are compared to the method of moments, which was validated against physical theory of diffraction.

The split-step-Fourier-based three-dimensional wave propagation prediction and finite-difference time-domain-based simulators are developed to show network scattering parameters of rectangular waveguide filters with horizontal and/or vertical windows as capacitive and/or inductive irises, respectively. The three-dimensional-split-step parabolic equ...

Novel, fringe wave integral equations that account for the diffraction from nonpenetrable wedges with both soft and hard boundaries are derived. Method of moments simulation of fringe waves generated by a plane wave that excites the wedge is performed using this fringe wave integral equation. The results are compared with the exact physical theory...

Physical theory of diffraction (PTD) is developed for the field scattered at a perfectly conducting rectangular plate. Grazing incidence and grazing scattering are analyzed. High-frequency asymptotic estimations are derived. Bistatic and monostatic scenarios are considered. Comparison is presented with known experimental and numeric results obtaine...

The 2015 IEEE Internat ional Conference on Antenna Measurements and Appl icat ions (CAMA 2015) was held in Chiang Mai, Thai land, 30 November2 December 2015. Most of our Administrative Committee members attended the conference. This new IEEE Antennas and Propagation Society (IEEE AP-S)-sponsored conference was hosted by General Chairs Dr. Monai Kra...

Fringe waves represent the diffracted field generated by the nonuniform/fringe surface currents concentrated in vicinity of sharp scattering edges. For perfectly conducting wedges, they have been studied in a number of publications. In this communication, fringe waves for a wedge with one face electric and the other magnetic are analyzed analytical...

Energy production in a safe and hazard free manner is one of the world׳s greatest concern. Since the inception of Kyoto Protocol, which was adopted in 1997 and entered into force in February 2005, countries have started to adopt different measures for emission reduction such as electricity generation from renewable energy sources; as the source is...

Method of moments (MoM) is applied in modeling and simulation for backscattering from a strip with one face soft and the other face hard (i.e., with Dirichlet and Neumann boundary conditions, respectively). The results are compared with high-frequency asymptotics (HFA), such as physical theory of diffraction (PTD) and theory of edge diffraction (TE...

Scattering from edges and/or tips (i.e., diffraction) has long been modeled using different approaches. Initially, it was handled analytically using high frequency asymptotics (HFA). Parallel to the development in computer technology diffraction has begun to be modeled using numerical approaches also. Here, method of moments (MoM) is used to model...

A parabolic equation toolbox (called PETOOL) has been developed in MATLAB with a user-friendly Graphical User Interface (GUI) for modeling radio-wave propagation over variable terrain and through homogeneous and inhomogeneous atmosphere (O. Ozgun, G. Apaydin, M. Kuzuoglu, L. Sevgi, Computer Physics Communications, 182, 2638–2654, 2011). The unique...

Edge and/or tip diffraction has long been investigated. Early attempts were analytical and called High Frequency Asymptotics (HFA). With the use of computers, numerical approaches have also appeared. In this study, two powerful numerical models, Method of Moments (MoM) and Finite Difference Time Domain (FDTD), are used in diffraction modeling on th...

Discontinuities such as tips and edges cause diffracted fields when electromagnetic waves interact with objects. Two-dimensional (2D) wedge with non-penetrable boundaries is a canonical structure which has long been investigated analytically and numerically for the understanding and extraction of diffracted waves. Multiple-diffraction has also been...

Method of moments (MoM) simulation of fringe waves generated by a line source that excites a perfectly reflecting wedge is introduced and compared with the exact physical theory of diffraction (PTD) fringe waves.

Method of Moments (MoM) is used to model guided wave propagation inside a nonpenetrable wedge waveguide and the results are validated against analytical mode-based exact solutions.

The above paper [1] is about the two-way split-step parabolic equation method (2W-SSPE) over irregular terrain, and claims that they have developed the “improved” version of the 2W-SSPE approach that has been proposed and validated by us in literature [2]-[11]. The paper [1] claims to derive the 2W-PE directly from 2D Helmholtz equation. They do th...

A novel Finite-Element Method - Parabolic-Equation (FEMPE) based MATLAB tool is developed. This calculates the electromagnetic field strength and path loss for one-way, forward propagation over multi-mixed irregular terrain paths through an inhomogeneous atmosphere, recommended by the ITU. The well-known smooth-Earth Millington curve-fitting model,...

B‐spline based finite element method parabolic wave propagation model is developed and tested against mode summation inside a parallel plate waveguide. The comprehensive numerical analysis of the solution of parabolic wave equation has been done. The algorithm is compared with mode summation in two dimensions. Excellent agreement is observed among...

AbstractA three‐dimensional (3D) finite‐difference time‐domain (FDTD) simulator is developed for the investigation of network (S‐) parameters of rectangular cross‐section waveguide filters. The simulator is calibrated against analytical LC equivalent models. Any number of horizontal or vertical windows can be located to act as capacitive or inducti...

A b-spline based finite element method parabolic wave propagation model is developed and tested against mode summation inside a parallel plate waveguide. The comprehensive numerical analysis of the solution of parabolic wave equation has been done. The algorithm is compared with mode summation in two dimensions. Excellent agreement is observed amon...

A three-dimensional (3D) finite-difference time-domain (FDTD) simulator is developed for the investigation of network (S-) parameters of rectangular cross-section waveguide filters. The simulator is calibrated against analytical LC equivalent models. Any number of horizontal or vertical windows can be located to act as capacitive or inductive irise...

Radiowave propagation models have long been used in long-range communication and/or radar systems. Different models use different sources. Observed and calculated results are therefore usually normalized, either against maximum or free-space values, or against values obtained above a non-penetrable flat Earth. This is acceptable and useful because...

The Split-Step-, Finite-Element-, and Finite-Difference-Method-based three-dimensional (3D) wave-propagation prediction simulators using the parabolic equation (PE) are calibrated against reference data derived from analytically exact solutions through tests inside a rectangular waveguide.

Method of Moments (MoM) modeling inside resonating structures is discussed and a novel approach called Multi-MoM (Mi-MoM) is proposed. Propagation inside a two-dimensional (2D) non-penetrable parallel plate waveguide is taken into account. The Mi-MoM results are compared with the analytical reference solution. Practical ways of different source rep...

This paper aims to provide a tutorial on computational electromagnetics (CEM), and simple MATLAB codes for sophisticated investigation of analytical and well-known numerical models. The problem of propagation inside a parallel-plate waveguide is used for this purpose.

Program download: http://cpc.cs.qub.ac.uk/summaries/AEJS_v1_0.html A MATLAB-based one-way and two-way split-step parabolic equation software tool (PETOOL) has been developed with a user-friendly graphical user interface (GUI) for the analysis and visualization of radio-wave propagation over variable terrain and through homogeneous and inhomogeneou...

Two-way, three-dimensional finite element and split-step Fourier-based parabolic equation (PE) wave propagation prediction algorithms are developed, and MATLAB-based simulators are introduced. The simulators are calibrated against analytical exact data derived from modal summation through tests inside rectangular waveguides.

A novel two-way finite-element parabolic equation (PE) (2W-FEMPE) propagation model which handles both forward and backward scattering effects of the groundwave propagation above the Earth's surface over irregular terrain paths through inhomogeneous atmosphere is introduced. A Matlab-based propagation tool for 2W-FEMPE is developed and tested again...

Model validation, data verification, and code calibration (VV&C) in applied computational electromagnetics is discussed. The step by step VV&C procedure is given systematically through canonical scenarios and examples. Propagation over flat-Earth with linearly decreasing vertical refractivity profile, having an analytical exact solution, is taken i...

Helmholtz's wave equation can be approximated by means of two differential equations, corresponding to forward and backward propagating waves each of which is in parabolic wave equation (PWE) form. The standard PWE is very suitable for marching-type numerical solutions. The one-way Fourier split-step parabolic equation algorithm (SSPE) is highly ef...

A novel MATLAB™-based split-step parabolic-equation (SSPE) propagation package is introduced for the prediction of electromagnetic surface-wave attenuation along multiple mixed irregular and lossy paths. The impedance boundary condition is implemented via the discrete mixed Fourier transform (DMFT). Irregular terrain modeling is handled via coordin...

This paper introduces a two-way split-step parabolic equation propagation tool (2W-SSPE), which is capable of handling both forward and backward scattered waves during groundwave propagation over an irregular terrain, through inhomogeneous atmosphere. The algorithm is calibrated and tested against reference data obtained with the help of image meth...

The aim of this study is to introduce, for the first time in the literature, a two-way FEMPE algorithm (2W-FEMPE), and to perform calibration tests of both two-way FEMPE and SSPE algorithms against the Image Method and the Geometric Optic (GO) + Uniform Theory of Diffraction (UTD).

Powerful propagation-prediction tools, based on the split-step Fourier-transform and the Finite-Element-Method (FEM) solutions of the parabolic equation (PE) are discussed. The parabolic equation represents one-way propagation, and is widely used in two-dimensional (20) groundwave propagation modeling. It takes the Earth's curvature, the atmospheri...

This article aims to present a development of reduced-delay finite impulse response digital filters with amplitude requirements using equiripple passband, peak constrained least squares stopbands, and nearly constant group delay in passband for real-time applications. The filter length, passband and stopband frequencies, ripples, and attenuation ar...

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-d...

Surface wave propagation along multi-mixed-paths with irregular terrain over spherical Earth in two-dimension (2D) is discussed. For the first time in the literature, sea-land-sea (island) transition problem including non-flat (hilly) islands is investigated systematically. A finite element method based multi-mixed path surface wave virtual propaga...

This paper presents the comparison of physical spline finite element method (PSFEM), in which differential equations are incorporated into interpolations of basic elements, with least-squares finite element method (LSFEM) and mixed Galerkin finite element method (MGFEM) on the numerical solution of one dimensional Helmholtz equation applied to an a...

This paper illustrates educational issues in electromagnetic compatibility (EMC) engineering in Switzer-land and presents the contents of courses and practical materials for EMC education at the University of Technology Zurich. After giving the fundamentals of theoretical part, practical applications have been given to make students and engineers a...

In this paper, the Finite-Element Method with weighted extended basis splines (web-spline) is described and used to obtain electromagnetic fields. This new approach is applied to two-dimensional rectangular, circular, and coaxial waveguides. The electric- and magnetic-field distributions of some modes are shown. The approximated solutions of web-sp...

A finite element method (FEM)-based surface wave propagation prediction simulator is developed. The simulator is tested and calibrated against analytical ray-mode models that also take into account the Millington recovery effects. It successfully calculates path losses over multimixed propagation paths at MF and HF frequency bands where the surface...

Light scattering properties from curved surface and cylinder are important in the area of propagation and remote sensing. The radar cross sections (RCS) of a dielectric thin curved surface and cylinder are obtained by employing a quasi-static approximation. The method is applicable to the electromagnetic (EM) scattering in general. However, the sim...

Finite Element Method (FEM) is one of the popular numerical methods when studying the complex geometries and arbitrary boundaries with inhomogeneous media for electromagnetics. However, mesh generation of standard FEM causes consumption in computation time for higher dimensions. This book presents the fundamental overview of electromagnetics and FE...

This paper illustrates web-splines and their implementations for electromagnetic problems such as waveguide of arbitrary domain. The cutoff wave numbers of modes for the coaxial waveguides are studied for illustrating the two dimensional concept. The numerical results have been compared with the analytical results. The significance of web-splines i...

Weighted extended (web) b-spline method is a new type of meshless finite elements without using mesh generation. The resulting web-method does not require any grid generation and, as a consequence, can be implemented very efficiently. This paper illustrates web-splines and their implementations for axisymmetrical formulation of electromagnetic prob...

A new electromagnetic model for curved dielectric surfaces and cylinder has been introduced. The model considers scatterers as a lossy dielectric body. The theoretical and simulation results have been compared with the literature and the model agrees with the published results of the hollow cylinder for which an exact solution exists. Figures of re...

The analyses presented in this study show the suitability of the proposed method to complex electromagnetic (EM) problems. The finite element method (FEM) which uses weighted extended basis-splines (web-splines) is applied to waveguides of arbitrary domain. The eigenvalue analysis is used to compare the proposed method with the standard FEM. Firstl...

This paper illustrates the weighted extended b-splines as basis functions of finite element method of arbitrary domain for waveguides. This method does not need mesh generation for applications. The results are compared with the finite element method with triangulation method using Lagrange basis functions. This method can be used in more electroma...

In this paper, a newly developed discrete multilayer propagation model using scattering theory is studied using rectangular lossy multilayer dielectric plates which model the walls, the streets, and avenues in urban areas. The model is presented to study radio wave propagation in street environments and to compare it with previous theoretical and e...

The finite element method, which uses weighted extended basis splines (web-splines) for solving two-dimensional electromagnetic wave equations, has been studied. The web-spline method, which does not need any mesh generation, is implemented easily. The web-spline method is more accurate numerical technique than the standard finite-element method. T...

Electromagnetic (EM) scattering from curved surface and cylinder is important in the area of propagation and remote sensing in order to determine EM properties of scatterers. The radar cross sections (RCS) of a dielectric thin curved surface and cylinder are obtained by employing a quasi-static approximation. The results are complemented by numeric...

This paper considers the weighted extended b-splines as basis function for finite element method in electromagnetics and compares with the standard finite element method applied to the two-point boundary value problems with different boundary conditions. This new approach, which provides more accurate results than standard finite element method, is...

This paper illustrates the weighted extended b-splines as basis functions for finite element method in electromagnetics. This method does not need mesh generation, and is applied to coaxial waveguide applications. The results are compared with the exact solutions in literature. The maximum relative error is used for comparison. This method can be u...

This study illustrates B-splines as basis function for FEM in electromagnetics. The wave equation for one dimension has been compared with the exact results. Accurate and fast results are obtained while increasing order. This method can be used in electromagnetic applications in order to get better approximation in higher dimensions

In this paper we have introduced new RCS model for the curved arbitrary dielectric surfaces, which can be thought as consisting of N rectangular lossy dielectric plates. Our simulations revealed that the developed model is applicable for a broad band of frequencies. This model can be used effectively for prediction of RCS in situation when dielectr...

The need for wireless communication data has increased considerably in past decades. In this paper we have introduced new propagation model for the streets and avenues in urban areas that can be thought as a waveguide for EM-waves. Using our developed model it is possible to calculate the contributions of each direct and scattered wave separately....

People are concerned about the dangers that can be possibly produced by electromagnetic (EM) radiation of devices in our daily life. This concern stipulated a lot of research aimed at finding these hazards. This study is aimed to analyze electrical parameters of various parts of man, which determine the level of hazards. By using curve-fitting meth...

In this work, electric field measurements are made in three categories. These are the near field measurements very close to the GSM phone for different phases (ringing, dialing, speaking) at the front, back, right and left sides of the phone, the electric field measurements at between 0-5 cm (1 cm intervals) away from the face and back of the GSM p...