This paper describes a finite-element approach to the quasi-TEM analysis of several different types of isolated and coupled microwave transmission lines. Both the first- and higher order ordinary ...elements, as well as singular and infinite elements, are used to solve for the potential and field distributions in the cross section of the line. Next, the cross-sectional field distribution is inserted in a variational expression to compute the capacitance per unit length of the line, and the effective permittivity and characteristic impedance of the line are obtained from the capacitance value. A perturbational approach is developed for estimating the losses due to conductor and dielectric dissipation and computing the attenuation constant. Both the upper and lower bounds for the capacitance and the characteristic impedance are found by solving the original and the corresponding dual problem. Lines treatable by this method may contain an arbitrary number of arbitrarily shaped conductors, including a system of conductors placed either above a single ground plane or between two parallel ground planes, and inhomogeneous dielectric regions that can be approximated Iocally by a number of homogeneous subregions. The results obtained using the finite-element procedure have been compared for various types of microwave transmission lines and have been found to agree well with available theoretical and measured data.
This paper presents a novel technique referred to herein as MNM for efficient iterative solution of MoM matrices over a broad frequency range. It utilizes a combination of techniques to reduce the ...number of iterations required to generate the solution including a special choice of the initial guess, and efficient preconditioning. Numerical results are presented to illustrate the application of the MNM to representative microwave circuit analysis problems.
In this paper the authors present a general subgridding scheme for enhancing the finite difference time domain (FDTD) algorithm. It is different from the conventional approaches in that it does not ...employ weighted averages of the electric or magnetic fields in the transition zone from the coarse to the fine grid regions, but employs a novel procedure instead for transferring the information between these two regions. We illustrate the application of the subgridding algorithm by considering refinement factor of 5, and provide validation of the results obtained for this case.
This paper proposes a technique for designing flat lenses using Field Transformation (FT), as opposed to Ray Optics (RO) or Transformation Optics (TO). The lens design consists of 10 layers of graded ...index dielectric in the radial direction and 5 layers in the longitudinal direction. The central layer in the longitudinal direction primarily contributes to a bulk of the phase transformation, while the other four layers, above and below this middle layer on either side, act as matching layers that help reduce the reflections introduced by the impedance mismatch at the interfaces of the middle layer. The paper compares the performance of the lens, so designed, with those based on the RO and TO techniques. We show that the proposed lens design using field transformation is broadband, has a better than 1 dB higher gain compared to the RO and TO based designs over a wider frequency band, and that its scan capability is superior as well.
An integral equation (IE) based solution procedure is presented for the rigorous analysis of scattering
from terrain profiles. The procedure uses characteristic basis function method (CBFM), which is
...hybridized with the forward-backward method (FBM), to reduce the storage requirements of the resultant
Method of Moments (MoM) impedance matrix, as well as to accelerate the solution procedure. Numerical
results in the form of induced current and scattered field are presented to assess the accuracy and
efficiency of the solution procedure.
Electromagnetic field computation may be carried out conveniently by using the finite element method (FEM). When solving open region problems using this technique, it becomes necessary to enclose the ...scatterer with an outer boundary upon which an absorbing boundary condition (ABC) is applied; analytically-derived ABCs have been used extensively for this purpose. Numerical absorbing boundary conditions (NABCs) have been proposed as alternatives to analytical ABCs. For the two-dimensional (2-D) Helmholtz equation, it has been demonstrated analytically that these NABCs become equivalent to many of the existing analytical ABs in the limit as the cell size tends to zero. In addition, the numerical efficiency of these NABCs has been evaluated by using as an indicator the reflection coefficient for plane and cylindrical waves incident upon an arbitrary boundary. We have extended this procedure to the study of the NABCs derived, for the three-dimensional (3-D) scalar and vector wave equations from the point of view of their numerical implementation in node- and edge-based FEM formulations, respectively.
A novel conformal finite-difference time-domain (CFDTD) technique for locally distorted contours that accurately model curved metallic objects is presented in this paper. This approach is easy to ...implement and is numerically stable. Several examples are presented to demonstrate that the new method yields results that are far more accurate than those generated by the conventional staircasing approach. Example geometries include cylindrical and spherical cavities, and a circular microstrip patch antenna. Accuracy of the scheme is demonstrated by comparing the results derived from analytical and Method of Moments (MoM) techniques.
The objective of this paper is to describe two parallel algorithms, one in the frequency and the other in the time domain, both of which have been designed for solving large problems on parallel ...computing platforms.
In this paper we identify some challenges in antenna designs-both small and large types-that we have recently encountered in the process of designing antennas for personal communication, GPS, UWB, ...Millimeter waves, BANs (body area networks), sensors, RFID, and other similar applications. The primary challenges in designing small antennas arise from the specifications that are often very demanding in terms of performance expectations, e.g., gain, bandwidth, pattern characteristics (including polarization), decreased sensitivity to the environment, etc., even as the above specs concurrently place severe restrictions on the size of the available real estate in which the antenna is to be placed. We should mention that even though the antenna itself may be small, the degrees of freedom (DOFs) associated with the problem description can still be large, especially when dealing with antenna/metamaterial composites, which often pose a considerable challenge when one attempts to simulate them. Needless to say that the topic of metamaterial has attracted considerable attention in recent years, as evidenced by the number of researcher contributing to the subject, who have been very prolific indeed. It would be presumptive to attempt to fully cover and renew these developments in this presentation-given the time limitation-because it would be impossible to do justice to the diverse away of facets that have all been grouped under the general umbrella of "Metamaterials." In view of this, we narrow our focus down to the topic of "Performance Enhancement of Small Antennas using Metamaterials," because such enhancements are certain to have a very large impact on communication antenna design, which, we believe to be a centerpiece topic of this conference. The first impression that comes to one's mind when one scans through and takes a cursory look at the vast array of publications that discuss antenna-material composites is that the metamaterials provide the proverbial "Midas touch," a veritable magic bullet for curing everything that ails the small antennas. If we were to compile a wish-list for the desired features of small antennas, we would most probably include: wide bandwidth in terms of both impedance match (return loss) and radiation pattern, high directivity, and conformal nature-to name just a few of the desirable attributes of the antennas that we might be designing for communication, RFID, GPS, LAN or BAN applications. Some of the small antenna/metamaterial composite type of configurations to be discussed in the presentation are shown in Figs. 1 through 5. For large antennas, the design goals are often very different, and the emphasis here may be to realize ultra-low sidelobes, reduce EMI, achieve superior EMC characteristics, etc., just to name a few. Here, the challenge often is how to model these large structures in an accurate and efficient manner so that their performance can be predicted reliably and confidently, before the antenna is actually fabricated-the motto being "Correct by Design," or CBD. Commercial softwares are often quite limited in their ability to handle the structures which require a problem description with a very large number of DOFs that could reach-or exceed- 10 9 unknowns, because of their complexity, multi-scale characteristics and inhomogeneous nature. With the advent of powerful computers such as the IBM/BlueGene (see Fig.6), it is now possible to solve problems of this magnitude accurately and efficiently. Illustrative examples of antenna configurations that fall in this category are: Array feeds for the Square Kilometer Array (SKA); coupling between two Phased arrays mounted on a large platform, e.g., the topside of a ship; and, the design of large doubly-curved subreflectors, comprised of multilayer FSS screens, for frequency reuse applications. A few of these representative large antenna problems are shown in Figs. 7 through 10, and would be discussed in the presentation.
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