Michael A. Khayat

Numerical evaluation of singular and near-singular potential Integrals

A simple and efficient numerical procedure using a singularity cancellation scheme is presented for evaluating singular and near-singular potential integrals with 1/R singularities. The procedure not only has several advantages over singularity subtraction methods, but also improves on some aspects of other singularity cancellation methods such as polar and Duffy transformations. A theoretical analysis is presented for triangles, quadrilaterals, tetrahedrons, bricks, and prisms, and numerical results are presented for triangles and prisms.

Body-Worn E-Textile Antennas: The Good, the Low-Mass, and the Conformal

Support of ever increasing applications for wireless data and communications on a body-centric platform requires novel antenna systems that can be integrated with the body-worn environment, while maintaining free-range of movement and minimal mass impact. E-textile antennas show great promise due to their ease of integration with other textile materials, and they are inherently low-mass and flexible relative to conventional antenna materials. Much attention has been given recently to multiple-antenna communication systems due to the increased performance compared to conventional single-antenna systems. For body-centric applications, the low-mass, flexibility, and integration simplicity of e-textile antennas can enable multiple-antenna systems, which otherwise would be precluded by the rigidity and mass of conventional antenna materials. Several examples of this are considered here with e-textile antennas in an array environment. A conventional microstrip array constructed with e-textiles is shown to have robust performance with moderate amounts of bending, similar to that which might be seen with body-worn arrays. In addition to the conventional array, a wideband multiple-antenna system to support a variety of wireless communication protocols, while maintaining polarization diversity and excellent coverage over a majority of the radian sphere is demonstrated.

Mutual coupling between reduced surface-wave microstrip antennas

An investigation of the mutual coupling between reduced surface-wave microstrip antennas is presented and compared with that for conventional microstrip antennas. Numerical results are presented from a theoretical analysis of the mutual coupling along with confirming experimental results. It is shown that for electrically thin substrates, the space-wave coupling, not the surface-wave coupling, is predominant for typical element spacing, for both the conventional and reduced surface-wave antennas. In addition, the mutual coupling behavior is examined using an asymptotic analysis, which demonstrates how the coupling falls off much faster with patch separation for reduced surface wave antennas compared to conventional microstrip patch antennas.

The dependence of the input impedance on feed position of probe and microstrip line-fed patch antennas

The impedance of a rectangular patch antenna fed by an inset microstrip transmission line was measured for various feed positions. The dependence found was then compared to theoretical predictions both for this geometry and for the similar case of an inset coaxial probe feed.

An Improved Transformation and Optimized Sampling Scheme for the Numerical Evaluation of Singular and Near-Singular Potentials

In this work we compare four transformations for numerically computing singular and near-sinuglar integrals. These schemes employ singularity cancellation methods in which a change of variables is chosen such that the Jacobian of the transformation cancels the singularity. Recently, a new singularity cancellation scheme, the arcsinh transformation, was presented for handling 1/R singularities. For singular integrals the method not only has several advantages over singularity subtraction methods, but also improves on some aspects of other singularity cancellation methods such as polar and Duffy transformations. One drawback of the scheme, however, is its inability to efficiently calculate near-singular integrals. To this end, we summarize and compare the performance of four transformations to handle near-singularities: the arcsinh transform, Duffy and polar transformations extended to treat near-singularities, and, a new scheme referred to as the radial-angular transformation. We find that the performance of the radial-angular transformation is much better than the other transformations for the near-singular case and comparable to them for the singular case. Subsequently, we describe a method for optimizing computation of the radial-angular transformation when a required accuracy is specified.

Simple and Efficient Numerical Evaluation of Near-Hypersingular Integrals

Simple and efficient numerical procedures for evaluating the gradient of Helmholtz-type potentials are presented. The convergence behavior of both normal and tangential components of the gradient is examined. It is also shown that the scheme for handling near-hypersingular integrals is effective for handling nearly singular potential integrals as well, so the same quadrature scheme may be used for both simultaneously.

A comparative study of a new GPS reduced-surface-wave antenna

A new global positioning system (GPS) antenna design based on the reduced-surface-wave (RSW) microstrip antenna concept is introduced. In addition to retaining the advantages common to microstrip antennas, these new GPS antennas will be shown to provide comparable performance to the most commonly used GPS antennas, including choke-ring designs. The reduced horizon and backside levels, and good circular polarization characteristics indicate that this new antenna design is ideal for high-precision GPS applications.

EIGER ™ : An open-source frequency-domain electromagnetics code

EIGERtrade is a general-purpose, 3D frequency-domain electromagnetics code suite consisting of a pre-processor (Jungfrau), the physics code (EIGER), and post processor (Moench). In order to better enable collaborative development, EIGERtrade version 2.0 has been approved for release as open source software under a GNU Public License. EIGERtrade is primarily an integral-equation code for both frequency-domain electromagnetics and electrostatics. This version includes the following Greens functions: 2D and 3D free space, symmetry-planes, periodic and layered media. There is a thin-wire algorithm as well as junction basis functions for attachment of a wire to a conducting surface, and also thin-slot models for coupling into cavities. The code is written in Fortran 90 using object-oriented design and has the capability to run both in parallel and serial.

An improved transformation and optimized sampling scheme for the numerical evaluation of singular and near-singular potentials

Simple and efficient numerical procedures using singularity cancellation methods are presented for evaluating singular and near-singular potential integrals. Four different transformations are compared and the advantages of the radial-angular transform are demonstrated. A method is then described for optimizing this integration scheme.

Mutual coupling between cylindrical probe-fed dielectric resonator antennas

The mutual coupling between two cylindrical probe-fed dielectric resonator antennas was measured in both the E- and H-planes for varying separations. The resulting measurements were shown to verify existing theoretical predictions and indicate the applicability of these types of antennas for array applications.