The multiband behavior of the fractal Sierpinski (1915) antenna is described. Due to its mainly triangular shape, the antenna is compared to the well-known single-band bow-tie antenna. Both experimental and numerical results show that the self-similarity properties of the fractal shape are translated into its electromagnetic behavior. A deeper physical insight on such a behavior is achieved by means of the computed current densities over the antenna surface, which also display some similarity properties through the bands.

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On the behavior of the Sierpinski multiband fractal antenna

Numerical Techniques in Electromagnetics is designed to show the reader how to pose, numerically analyze, and solve electromagnetic (EM) problems. It gives them the ability to expand their problem-solving skills using a variety of available numerical methods. Topics covered include fundamental concepts in EM; numerical methods; finite difference methods; variational methods, including moment methods and finite element methods; transmission-line matrix or modeling (TLM); and Monte Carlo methods. The simplicity of presentation of topics throughout the book makes this an ideal text for teaching or self-study by senior undergraduates, graduate students, and practicing engineers.

Numerical Techniques in Electromagnetics, Second Edition

Photoconductive antennas (PCAs) have been extensively utilized for the generation and detection of both pulsed broadband and single frequency continuous wave terahertz (THz) band radiation. These devices form the basis of many THz imaging and spectroscopy systems, which have demonstrated promising applications in various industries and research fields. The development of THz PCA technology through the last 30 years is reviewed. The key modalities of improving device performance are identified, and literature is reviewed to summarize the progress made in these areas. The goal of this review is to provide a collection of all relevant literature to bring researchers up to date on the current state and remaining challenges of THz PCA technology.

https://www.spiedigitallibrary.org/journals/optical-engineering/volume-56/issue-1/010901/Review-of-terahertz-photoconductive-antenna-technology/10.1117/1.OE.56.1.010901.pdf

Review of terahertz photoconductive antenna technology

A wireless communication system consists of various passive components, including antennas, directional couplers, phase shifters, and filters. These components have many dimensional parameters that must be determined. For instance, a coupled line section has line width, gap between the coupled lines, and the length of the line as the parameters to be determined. Identifying these parameters through trial and error is ineffective. Meanwhile, the mathematical approach may be very complex and may use some assumptions in the calculation that introduces differences between the calculated dimensions and the actual dimensions.

Multiobjective Optimization

The theoretical limit for small antenna performance that was derived decades ago by Wheeler and Chu governs design tradeoffs for size, bandwidth, and efficiency. Theoretical guidelines have also been derived for other details of small antenna design such as permittivity, aspect ratio, and even the nature of the internal structure of the antenna. In this paper, we extract and analyze experimental performance data from a large body of published designs to establish several facts that have not previously been demonstrated: (1) The theoretical performance limit for size, bandwidth, and efficiency are validated by all available experimental evidence. (2) Although derived for electrically small antennas, the same theoretical limit is also generally a good design rule for antennas that are not electrically small. (3) The theoretical predictions for the performance due to design factors such as permittivity, aspect ratio, and the internal structure of the antenna are also supported by the experimental evidence. The designs that have the highest performance are those that involve the lowest permittivity, have an aspect ratio close to unity, and for which the fields fill the minimum size enclosing sphere with the greatest uniformity. This work thus validates the established theoretical design guidelines.

Experimental Validation of Performance Limits and Design Guidelines for Small Antennas

Graphene-based devices constitute a pioneering field of research for their extraordinary electromagnetic properties. The incorporation of appropriate models into numerical simulators is necessary in order to take advantage of these properties. In this work, we propose a method to incorporate graphene-sheet models into the FDTD method. The use of vector-fitting techniques expands the permittivity of graphene into a rational function series of complex conjugate pole-residue pairs, which is implemented into FDTD by an auxiliary differential equation formulation. Simple waveguiding problems validate our approach.

FDTD Modeling of Graphene Devices Using Complex Conjugate Dispersion Material Model

This letter presents a new hybrid method that efficiently combines two versatile numerical techniques, viz., the finite difference time domain (FDTD) and the method of moments in the time domain (MoMTD). The hybrid method is applicable to complex geometries comprising arbitrary thin-wire and inhomogeneous dielectric structures. It employs the equivalence theorem to separate the original problem into two subproblems: (1) the region containing the wires, which is analyzed by using the MoMTD, and (2) the dielectric zone that is modeled with the FDTD. The application of the method is illustrated by analyzing two canonical problems involving thin wires and inhomogeneous media.

A hybrid technique combining the method of moments in the time domain and FDTD

This paper describes an extension of the alternating direction implicit finite-difference time-domain (ADI-FDTD) method to analyze problems involving Debye media.

Extension of the ADI-FDTD method to Debye media

Some recent developments and extensions of the method of moments for analyzing, in the time domain, the interaction of transient electromagnetic waves with perfect electric conductors are described. The electric and magnetic time-domain integral equations (TDIEs) are formulated and their characteristics briefly discussed. Some issues involved in the formulation and solution of the thin-wire electric-field integral equation are examined. The solution of the magnetic- and electric-field integral equations for bodies modeled by patches is considered. The problem of the instabilities that appear in the solution of the TDIEs is addressed. The possibilities of using postprocessing of the time-domain data to visualize the history of electromagnetic phenomena are illustrated. >

Time-domain integral equation methods for transient analysis

This paper describes a hybrid technique directly operating in time domain that combines the finite element time domain (FETD), the finite-difference time-domain (FDTD) and the integral-equation-based method of moments in the time domain (MoMTD) techniques to analyze complex electromagnetic problems involving thin-wire antennas radiating in the presence of inhomogeneous dielectric bodies whose shape can be arbitrary. The method brings together the ability of the FDTD scheme to deal with arbitrary material properties, the versatility of the FETD to accurately model curved geometries, and that of the MoM to analyze thin-wire structures. Working in the time domain provides wide-band information from a single execution of the marching-on-in-time procedure and simplifies the interfacing of the FE and MoM methods with the FDTD, an approach specifically designed for time domain analysis. Numerical results that validate the hybrid method and show its capabilities are presented in the paper.

A hybrid time-domain technique that combines the finite element, finite difference and method of moment techniques to solve complex electromagnetic problems

Rafael Gomez Martin

Papers

FDTD Modeling of Graphene Devices Using Complex Conjugate Dispersion Material Model

A hybrid technique combining the method of moments in the time domain and FDTD

Extension of the ADI-FDTD method to Debye media

Time-domain integral equation methods for transient analysis

A hybrid time-domain technique that combines the finite element, finite difference and method of moment techniques to solve complex electromagnetic problems