Siniša Antonijević

Time-Domain Generalized Telegrapher's Equations for the Electromagnetic Field Coupling to Finite Length Wires Above a Lossy Ground

In this paper, a time-domain variant of the generalized telegraphers equations for transient electromagnetic field coupling to a finite-length wire above a lossy half-space is derived. The approach is fully based on the thin-wire antenna theory. The lossy ground effects are taken into account by means of the reflection coefficient approximation. The obtained equations are handled numerically via the Galerkin-Bubnov indirect boundary element method. Computational examples are presented for the case of a single-wire line excited by an electromagnetic pulse excitation source. The obtained results for the induced current along the line are compared with those obtained using 1) the method of moments solution of the electric field integral equation implemented in the numerical electromagnetics code (NEC-4), and 2) the transmission line (TL) theory. It is shown that the results obtained by the proposed method are in excellent agreement with those of NEC-4. It is also shown that the TL approximation yields in general results which are in reasonably good agreement with the full-wave results, especially for the early time response and even beyond the limits of the accuracy of the TL theory. The TL theory can, however, give accurate results only for times before the arrival of the first reflection from the TL terminations and it fails to reproduce accurately the dispersion effects occurring after the first reflection.

Transient Response of Straight Thin Wires Located at Different Heights Above a Ground Plane Using Antenna Theory and Transmission Line Approach

Transient electromagnetic field coupling to straight thin wires parallel to each other and located at different heights above a perfectly conducting or dielectric ground plane is analyzed using wire antenna theory and a transmission line method. The time-domain antenna theory formulation is based on a set of the space-time Hallen integral equations. The transmission line approximation is based on the corresponding time-domain Telegraphers equations. The space-time integral equations arising from the wire antenna theory are handled by the time-domain Galerkin-Bubnov scheme of the indirect boundary element method. The time-domain Telegraphers equations are solved using the finite-difference time-domain method. Time-domain numerical results obtained with both approaches are compared to the results computed via NEC 2 code combined with an inverse Fourier transform procedure. Some illustrative comparisons of results obtained by means of antenna theory and transmission line approach are presented throughout the paper.

Electromagnetic field coupling to overhead wires: Comparison of wire antenna and transmission line model in the frequency and time domain

The paper deals with different approaches for the analysis of electromagnetic field coupling to overhead wires of finite length based on the wire antenna theory, and transmission line method (TLM). The formulation based on the wire antenna theory in the frequency domain is based on the corresponding Pocklington equation, while the time domain formulation is based on the space-time Hallen integral equation. Transmission line model is based on the frequency and time domain Telegraphers equations.. The integro-differential and integral realtionships arising from the wire antenna theory are numerically handled via the frequency and time domain Galerkin-Bubnov scheme of the Indirect Boundary Element Method (GB-1BEM), repectively. The transmission line equations are treated using the Finite Difference Time Domain (FDTD) Method. Some illustrative numerical results obtained via different approaches are presented in the paper.

A Novel Time-Domain Reflection Coefficient Function: TM Case

In determining electromagnetic transient response of structure placed above the half space, the half space properties can be taken into account via the reflection coefficient (RC) approximation. The choice of an RC function used in RC approximation is often important with regards to accuracy and computational efficiency of the overall method. In this paper, a new time-domain RC function for the case of TM polarization is presented. The function is derived using Gaver-Stehfest algorithm for numerical inverse Laplace transform and does not require the use of Bessel functions. The resulting formulation is rather simple, and, as the results indicate, accurate and computationally efficient.

Some computational aspects of using current and voltage sources in electromagnetic models of lightning return strokes

The paper deals with some computational aspects of modeling the lightning return strokes using the full wave model. The electromagnetic model of lightning return stroke is based on the thin wire antenna theory and the related Pocklington integro-differential equation in the frequency domain while the corresponding transient response is obtained by means of hybrid (analytical and numerical) version of the Inverse Fourier Transform. The Pocklington equation is solved by the Galerkin-Bubnov Indirect Boundary Element Method (GB-IBEM). Special attention is given to the computational differences arising from the usage of current and voltage source, respectively.

Optimized numerical models of thin wire above an imperfect and lossy ground for GPR statistics

This contribution aims to demonstrate the ability of advanced time techniques to deal with Ground Penetrating Radar (GPR) applications. It is recognized that GPR systems are subjected to complex environment: parameters from setup (antennas) and environment are hardly ever known with an infinite precision. This issue is mainly due to intrinsic uncertainties (heights of antennas, soil electrical properties for instance) and may be illustrated trough time modeling of thin wire located above a lossy ground. In order to tackle the problem, the aim of this paper is to combine advanced time techniques with stochastic methods to properly access relevant statistics about GPR time responses.

Galerkin-Bubnov Boundary Element Analysis of the Yagi-Uda Array

Currents induced along the elements of a wire antenna arrey are calculated by solving the set of electric field integral equations (EFIEs). These coupled integral equations are handled via the Galerkin-Bubnov Boundary Element Method (GB-BEM). Once obtaining the currents along the wires an electric field radiated ba wire structure and the corresponding input ompedance are evaluated.

Development of electromagnetic simulators for Ground Penetrating Radar

This paper presents two electromagnetic simulators based on the Finite-Difference Time Domain (FDTD) technique and Boundary Element Method (BEM), for Ground Penetrating Radar applications. The first simulator is the new open-source version of the software gprMax, which employs Yees algorithm to solve Maxwells equations by using the FDTD method and includes advanced features allowing the accurate analysis of realistic scenarios. Additionally, E2GPR is a freeware package conceived to ease the use of gprMax: it assists in the creation, modification and analysis of two-dimensional models and can be used to plot results. The second simulator is TWiNS-II: this is free software for the analysis of multiple thin wires in the presence of two media, implementing the Galerkin-Bubnov Indirect BEM; calculations can be undertaken in the frequency or time domain. These tools have been developed by Members of the COST Action TU1208 “Civil Engineering Applications of Ground Penetrating Radar.”

Transient response of multiple thin wires located at different heights above a dielectric half-space

Transient electromagnetic field coupling to multiple parallel wires located at different heights above a dielectric half-space is analyzed using the wire antenna theory, and transmission line (TL) method. The wire antenna theory formulation in the time domain is based on the set of the space-time Hallen integral equations. Transmission line approximation is based on the time domain telegraphers equations. The space time integral equations arising from the wire antenna theory are treated by the time domain Galerkin-Bubnov scheme of the indirect boundary element method (TD GB-IBEM). The corresponding telegraphers equations are solved using the finite difference time domain (FDTD) Method. Time domain numerical results obtained with both approaches are compared to the results computed via NEC 2 code combined with Inverse Fourier transform (IFT).

Time Domain Measure for Power Flow of Thin Wire Electromagnetic Field

Time domain power measure associated with the currents and charges induced on straight horizontal wires above perfect ground is proposed. The formulation is based on a set of coupled space-time Hallen integral equations. The time domain power flow measure is given by the negative time derivative of the spatial integral of the squared current and charge along the wires