A. Sebak

Array near field focusing

Antenna arrays are normally characterized in terms of their far field radiation patterns, beam width and directive gain. However, for some applications the array is focused in the near field. The focus size is determined in terms of the near field properties of the array. The focusing is done through adjusting the phase of the elements of the array. The simulations are done using the method of moments (MoM). Two methods for adjusting the phase are compared. The focusing techniques analyzed here have several applications including imaging apertures, for which high spatial resolution is of great importance.

A K-band circularly polarized cavity backed dielectric resonator

A high efficiency linear polarized antenna consisting of a patch fed cavity has already been developed for use in personal communication terminals. It possesses several desirable features for active array applications, particularly the ease of RF component integration and heat removal. As part of the continued development of this antenna, it is very desirable to extend the capabilities to include future circularly polarized (CP) applications. The logical step for achieving the CP performance is to replace the linearly polarized feed patch with a single point feed CP patch. A single point feed is preferred in order to maintain the simplicity of the feed network. This approach, however, has a major drawback of possessing a narrow axial ratio bandwidth. To improve the axial ratio bandwidth, an alternative CP feed antenna is required. Research in circularly polarized dielectric resonator antennas (DRAs) has shown that a wide axial ratio bandwidth can be achieved from a single point fed DRA. The performance of the dielectric cross within a cavity structure is investigated. The optimization of the geometry and the effects on overall operation are discussed.

Two dimensional hexagonal TLM node and velocity error correction

The original two-dimensional TLM (transmission line matrix) method is based on a rectangular lattice or orthogonal transmission lines. The authors introduce a node which is based on a lattice with hexagonal symmetry. The advantage of the node is that the velocity error is only weakly dependent on the direction of the propagation. Therefore, for a specific frequency the amount of velocity error can be determined and eliminated.<<ETX>>

Electromagnetic wave scattering by a two layered piecewise homogeneous confocal elliptic cylinder

The scattering properties of a homogeneous elliptic cylinder with a confocal dielectric or magnetic coating are investigated analytically. The method of separation of variables is used to determine, exactly, the field distributions in each region for both transverse electric and transverse magnetic excitations. The technique can be easily extended to handle any number of layers. The behavior of the scattered field in the far zone is illustrated with numerical results for different core and coating material types, axial ratios, and electrical sizes.

Transmission-line matrix (TLM) method for scattering problems

Abstract In this paper we discuss the application of the TLM method to electromagnetic scattering and radiation problems. A general formulation based on the equivalence principle is developed for exciting structures with arbitrary field distributions. Various methods of realizing absorbing boundary conditions are presented. The sample computation provided illustrates the accuracy and efficiency of the formulation for a simple two-dimensional scattering problem.

Minimizing the computational cost and memory requirements for the capacitance calculation of 3-D multiconductor systems

A new approach is presented which minimized the computational cost and memory requirements for capacitance calculations of three-dimensional multiconductor systems. The proposed approach, based on the integral equation method (IEM), calculated the capacitance of three-dimensional geometry of ideal conductors in two stages. In the first stage, the integral equation method was used to obtain the charge distribution on each conductor in isolation. In the second stage, the multiple interaction (coupling) among the conductors was included by applying the IEM to the whole structure and considering the charge distribution, obtained in the first stage, as a discretized entire domain basis function. The order of the interaction matrix was thus reduced to the order of conductors in the structure. The proposed method was tested for various geometries and it resulted in tremendous savings in computational time and memory storage; moreover, it gave very good accuracy in comparison with the classical integral equation method. >

Using the Complex Images Method To Analyze Printed Antennas in Multilayer Dielectric Media

This paper presents an efficient full wave numerical analysis method for three dimensional microstrip structures inside a stratified media. The method can analyze both vertical and horizontal components of the currents. The conducting structures are modeled using a mixed potential integral equation. The boundary conditions on the interfaces between dielectric layers are satisfied through the use of appropriate dyadic Greens functions in the spectral domain. The numerical evaluation of the Sommerfeld integrals that are encountered during the transformation of the Greens function to the spatial domain is avoided using the complex images method (CIM). A modified CIM is proposed for efficient solution of vertical conductors currents. The modification maintains the rigorous nature of the full-wave analysis method while achieving the same efficiency for both vertical and horizontal components of currents. The resulting algorithm is found to be a versatile and efficient numerical analysis tool for microstrip antennas. The accuracy of the method is tested against commercially available full wave analysis packages. Good agreement is obtained for a wide class of stacked microstrip antennas.

Multiple Scattering by Dielectric Cylinders Using a Multifilament Current Model

A numerical method is presented for the problems of transverse magnetic (TM) and transverse electric (TE) multiple scattered fields from homogeneous dielectric and imperfectly conducting parallel cylinders. The numerical solution uses fictitious filamentary sources to simulate the field scattered by and transmitted into the cylinders. The currents of the fictitious sources are solved for subject to the boundary conditions. Numerical results, for multiple scattering by two cylinders having different parameters, are given and compared with method of moments solutions.

Holographic antenna efficiency

The holographic antennas efficiency is formulated to determine the holographic antenna dimensions and feed patterns that generate optimal performance. This efficiency comprises three main contributing sources of loss, namely, the spillover, taper, and, termination efficiencies. Antenna measurements using a linear tapered slot antenna as a holographic antenna feed confirm the accuracy of the efficiency derivation.

Unrelated Illumination Approach for the Reconstruction of Three-Dimensional Inhomogeneous Dielectric Bodies

The unrelated illumination method is used to estimate the complex permittivities of three-dimensional inhomogeneous dielectric bodies. Starting from the integral representation of the electric field and using the method of moments, the object under investigation is illuminated by a group of unrelated incident fields. Computer simulations show that the method can be used to overcome the severe ill-posedness of the three-dimensional problem even in the presence of noise and with the use of only one detector to measure the external scattered field. The accuracy of the method is tested for various contrasts, number of scatterers and different cell sizes. The method is further tested using a model for the human head and a 180-cell model of the human body and very accurate reconstruction is obtained.