Broadband cloaking with volumetric structures composed of two-dimensional transmission-line networks

The cloaking performance of two microwave cloaks, both based on the recently proposed transmission-line approach, are studied using commercial full-wave simulation software. The cloaks are shown to be able to reduce the total scattering cross sections of metallic objects of some restricted shapes and sizes. One of the studied cloaks is electrically small in diameter, and the other is electrically large, with the diameter equal to several wavelengths.Comment: 6 pages, 7 figure

Analysis of microstrip antennas by multilevel matrix decomposition algorithm

Integral equation methods (IE) are widely used in conjunction with Method of Moments (MoM) discretization for the numerical analysis of microstrip antennas. However, their application to large antenna arrays is difficult due to the fact that the computational requirements increase rapidly with the number of unknowns N. Several techniques have been proposed to reduce the computational cost of IE-MoM. The Multilevel Matrix Decomposition Algorithm (MLMDA) has been implemented in 3D for arbitrary perfectly conducting surfaces discretized in Rao, Wilton and Glisson linear triangle basis functions . This algorithm requires an operation count that is proportional to N·log2N. The performance of the algorithm is much better for planar or piece-wise planar objects than for general 3D problems, which makes the algorithm particularly well-suited for the analysis of microstrip antennas. The memory requirements are proportional to N·logN and very low. The main advantage of the MLMDA compared with other efficient techniques to solve integral equations is that it does not rely on specific mathematical properties of the Green's functions being used. Thus, we can apply the method to interesting configurations governed by special Green's functions like multilayered media. In fact, the MDA-MLMDA method can be used at the top of any existing MoM code. In this paper we present the application to the analysis of large printed antenna arrays.Peer ReviewedPostprint (published version

Green's functions in layered media: Imaginary axis integration and asymptotic behavior

This paper presents an efficient technique for evaluating Green’s functions associated to layered media, when cast in the space domain as Sommerfeld integrals. The theoretical developments needed to set up the numerical algorithm throw a new light on the asymptotic behavior of these Green’s functions for large transverse source-observer distances.The authors wish to thank Rich Hall from Boulder Microwave Technologies Inc.and Yan Brand from Ecole Polytechnique Fkdkrale de Lausanne for helpful discussion and advice

Integral Equation Analysis of Plane Wave Scattering by Coplanar Graphene-Strip Gratings in the THz Range

The plane wave scattering and absorption by finite and infinite gratings of free-space standing infinitely long graphene strips are studied in the THz range. A novel numerical approach, based on graphene surface impedance, hyper-singular integral equations, and the Nystrom method, is proposed. This technique guarantees fast convergence and controlled accuracy of computations. Reflectance, transmittance, and absorbance are carefully studied as a function of graphene and grating parameters, revealing the presence of surface plasmon resonances. Specifically, larger graphene relaxation times increases the number of resonances in the THz range, leading to higher wave transmittance due to the reduced losses; on the other hand an increase of graphene chemical potential up-shifts the frequency of plasmon resonances. It is also shown that a relatively low number of graphene strips (>10) are able to reproduce Rayleigh anomalies. These features make graphene strips good candidates for many applications, including tunable absorbers and frequency selective surfaces.Comment: 11 pages, 26 figure

Two Techniques for the Efficient Numerical Calculation of the Green's Functions for Planar Shielded Circuits and Antennas

In this paper we present new contributions to the computation of the Green's functions arising in the analysis of mul- tilayered shielded printed circuits and antennas. First the quasi- static term of the spectral domain Green's functions is extracted so that the convergence of the reminder dynamic modal series is enhanced. Moreover, it is shown that by extracting a second-order quasi-static term the convergence is further improved. In regard to the quasi-static terms they are computed in the spatial domain by numerically evaluating the associated spatial images series. Then a new and efficient technique is developed for the summation of the slowly convergent modal series. The technique can be viewed as the application of the integration by parts technique to discrete se- quences and greatly accelerates the convergence rate of the series involved. It is shown that the new algorithm is numerically very robust and leads to a drastic reduction in the computational ef- fort and time usually required for the numerical evaluation of the shielded Green's functions.Universidad Politécnica Federal de Lausann

The Summation by Parts Algorithm: A New Efficient Technique for the Rapid Calculation of Certain Series Arising in Shielded Planar Structures

This paper presents a new technique for the convergence acceleration of a large class of series often arising in electromagnetic problems. The technique is based on the recursive application of the integration-by-parts technique to discrete sequences, thus the given name of the "summation-by-parts" technique. It is shown that the new technique greatly enhances the convergence rate of the series treated, and very small relative errors are obtained by performing a few simple operations. The new technique is applied to the efficient numerical calculation of the Green's functions in a parallel-plate waveguide.Universidad Politécnica Federal de Lausanne (EPFL

An efficient technique for the rigorous analysis of shielded circuits and antennas of arbitrary shape

This paper presents an efficient technique for the analysis of arbitrary shaped circuits and antennas when embedded in metal-lic cavities. The technique uses the integral equation formulation and is based on the repre-sentation of the rigorous spatial domain boxed Green’s functions in terms of modal series ex-pansions. A new analytical integration scheme extended to arbitrary triangular domains is de-rived and asymptotic extraction procedures are used to enhance the convergence of the integral equation kernel. The technique thus derived is very efficient computationally and the simulated results show good agreement with measurements.The present work has been developed at LEMA/EPFL under contract No. 11698/95/NL/SB with ESA/ESTEC in collaboration with ALCATEL SPACE, Toulouse, France and CASA, Madrid, Spain

Green's Functions in Lossy Layered Media: Integration Along the Imaginary Axis and Asymptotic Behavior

This paper presents an efficient technique for eval- uating Green's functions associated to layered media, when for- mulated as Sommerfeld integrals in the space domain. The key step in the formulation is that Sommerfeld integrals are computed choosing a suitable integration path which is closed through the imaginary axis of the complex spectral plane. It is shown that with this original choice of the integration contour, the numerical effort usually involved in the evaluation of Sommerfeld integrals can be greatly reduced, specially when large source-observer distances are involved. One asset of this technique is that it can be easily incorpo- rated into integral equation based CAD packages for the efficient analysis of complex printed microwave circuit and antennas. In ad- dition, the theoretical developments needed to set up the numerical algorithm throw a new light on the asymptotic behavior of the lay- ered media Green's functions for large source-observer distances.Universidad Politécnica Federal de Lausann

The weighted averages algorithm revisited

The classic weighted averages (WA) algorithm for the evaluation of Sommerfeld-like integrals is reviewed and reappraised. As a result, a new version of the WA algorithm, called generalized WA, is introduced. The new version can be considered as a generalization of the well established Holder and Cesaro means, used to sum divergent series. Generalized WA exhibits a more compact formulation, devoid of iterative and recursive steps, and a wider range of applications. It is more robust, as it provides a unique formulation, valid for monotonic and oscillating functions. The implementation of the new version is easier and more economical in terms of basic operations. Preliminary numerical examples show that generalized WA also outperforms in terms of accuracy the classic WA algorithm, which is currently recognized as the most competitive algorithm to evaluate Sommerfeld integral tails