Dimitra I. Kaklamani

Circular and Elliptical CPW-Fed Slot and Microstrip-Fed Antennas for Ultrawideband Applications

This letter presents novel circular and elliptical coplanar waveguide (CPW)-fed slot and mictrostip-fed antenna designs targeting the 3.1¿10.6 GHz band. The antennas are comprised of elliptical or circular stubs that excite similar-shaped slot apertures. Four prototypes have been examined, fabricated and experimentally tested, the three being fed by a CPW and the fourth by a microstrip line, exhibiting a very satisfactory behavior throughout the 7.5 GHz of the allocated bandwidth in terms of impedance matching

Aspects of the Method of Auxiliary Sources (MAS) in computational electromagnetics

(hbox VSWR¿2)

Electromagnetic scattering analysis of coated conductors with edges using the method of auxiliary sources (MAS) in conjunction with the standard impedance boundary condition (SIBC)

, radiation efficiency and radiation pattern characteristics. Measured impedance bandwidths of beyond 175% will be presented.

Accuracy analysis and optimization of the method of auxiliary sources (MAS) for scattering by a circular cylinder

The method of auxiliary sources (MAS) is a numerical technique, alternative to the standard surface integral-equation formulation, suitable for solving elliptic boundary-value problems appearing in electromagnetic scattering analysis, antenna modeling, waveguide structures, etc. This paper provides an overview of MAS as applied to computational electromagnetics. The fundamentals of MAS are presented and its advantages over the method of moments are highlighted, while special emphasis is given to a number of advanced issues. Moreover, a selection of recent developments in the method is presented, with a detailed description of several challenging topics. Finally, the potential applicability of the method to a broader range of problems is contemplated.

RADIATION OF A DIPOLE IN AN INFINITE TRIAXIAL ANISOTROPIC MEDIUM

A novel combination of the method of auxiliary sources (MAS) and the standard impedance boundary condition (SIBC) is employed in the analysis of transverse magnetic (TM) plane wave scattering from infinite, coated, perfectly conducting cylinders with square cross sections. The scatterer is initially modeled by a SIBC surface and the scattering mechanism is subsequently analyzed via MAS. Although SIBC as well as MAS possess theoretical limitations with regard to an edge, the numerical results show that the MAS/SIBC method provides results of high accuracy for a range of structures with edges. The SIBC modeling of coated conductors with edges has previously been investigated in the literature and thus, this work focuses on comparing MAS and the method of moments (MoM) for SIBC surfaces (MoM/SIBC). A detailed complexity analysis shows that the MAS/SIBC method is, under certain conditions, more efficient than the MoM/SIBC method, proving that the proposed novel combination is a powerful and advantageous computational tool.

An improved accuracy version of the method of auxiliary sources for computational electromagnetics

This paper presents a rigorous accuracy analysis of the method of auxiliary sources (MAS), when applied to scattering problems. A benchmark, canonical geometry, consisting of a perfectly conducting, infinite, circular cylinder, is chosen for clarity and simplicity. For this particular structure it is shown that the MAS square matrix can be inverted analytically, yielding exact mathematical expressions for the discretization error and the condition number of the pertinent linear system. It is also demonstrated that the error increases very abruptly for source locations associated with the characteristic eigenvalues of the scattering geometry, precisely as predicted in theory. Various plots depict comparisons between analytical and computational data for the boundary condition error, and all occurring discrepancies are fully explained. Among several important results of the analysis, the fundamental MAS question concerning the optimal location of the auxiliary sources is thoroughly investigated and resolved on the grounds of error minimization.

Statistical Analysis for On-Body Spatial Diversity Communications at 2.45 GHz

Abstract The radiation of an elementary dipole placed inside an infinite triaxial anisotropic medium is analyzed. A Fourier analysis is employed to compute the field which is represented by using a dyadic formulation. The near and far field expressions are obtained by pursuing integration of the Fourier integrals. Conventional spherical scalar wave functions are employed to represent the dyadic Greens functien. Singularity source terms of the Greens function dominant in the near field region, are treated independently. Two separate spherical waves compose the far field, where also a non-zero radial term appears.

Service Composition: State of the art and future challenges

The method of auxiliary sources (MAS) is normally applicable to electromagnetic problems involving structures of significant thickness, so that an adequately large distance between source and collocation points is guaranteed. For thin or open geometries the accuracy of the method is depleted, due to numerical instabilities caused by the highly singular terms of the dyadic Greens function (DGF). In this paper a modified MAS (MMAS) is developed to circumvent this particular difficulty. Higher order terms of the DGF are numerically calculated by introducing a canonical grid, where derivatives can be accurately computed via a discrete scheme, unlike standard MAS, where the DGF analytical, problematic expression is invoked instead. This procedure is equivalent to the involvement of auxiliary currents and charges in the solution, instead of the elementary source fields used in standard MAS.

An integrated remote monitoring platform towards Telehealth and Telecare services interoperability

An investigation of the fading experienced by on-body diversity channels at 2.45 GHz is presented by focusing on the effects of the receive antennas position and the human body movement. This investigation is based on the conduction and analysis of signal measurements in an indoor office environment using bodyworn antennas. Three principal combining techniques, namely selection combining (SC), equal gain combining (EGC) and maximal ratio combining (MRC) are considered. A statistical characterization of the fading experienced by dual diversity on-body channels is performed in terms of first and second order statistics. Our investigations have shown that among several distributions tested, the α - μ distribution provides sufficient fit to measured combined signal envelopes and also offers a good approximation to second order statistics for the majority of test cases.

Subcarrier allocation algorithms for multicellular OFDMA networks without Channel State Information

Service discovery and service composition constitute challenging tasks of service provisioning. Service composition is especially gaining on importance, as it can produce new composite services with features not present in the individual services. Many methods have been proposed over the years to address these issues. Simple Mobile Services (SMS) is a project aiming at creating innovative tools that will introduce a new class of mobile services enabling individuals and small businesses to become service providers. In this paper an attempt is made to present an overview of all existing techniques on service composition and examine them in the context of SMS. The enumeration of the techniques is complete and focuses mostly on recent approaches. Moreover, service composition is discussed under the prism of mass service provisioning by mobile operators where some techniques currently seem to be more suitable than others.