Ahmed A. Sakr

An Integral Equation Formulation for TM Scattering by a Conducting Cylinder Coated with an Inhomogeneous Dielectric/Magnetic Material

A volume-surface integral equation (VSIE) formulation is developed for determining the electromagnetic TM scattering by a two-dimensional conducting cylinder coated with an inhomogeneous dielectric/magnetic material. The electric fleld integral equations (EFIEs) are utilized to derive the VSIE. The surface EFIE is applied to the conducting surface, while the volume EFIE is applied to the coating region. By employing the surface and equivalence principles, the problem is reduced into a set of coupled integral equations in terms of equivalent electric and magnetic currents radiating into unbounded space. The moment method is used to solve the integral equations. Numerical results for the bistatic radar cross section for difierent structures are presented. The well-known exact series-solution for a conducting circular cylinder coated with multilayers of homogeneous materials is used along with the available published data to validate the results. The in∞uence of using coatings with double-positive (DPS) and/or double-negative (DNG) materials on the radar cross section is investigated.

Electromagnetic TE scattering by a conducting cylinder coated with an inhomogeneous dielectric/magnetic material

The problem of electromagnetic TE scattering by an infinitely long conducting cylinder coated with an inhomogeneous dielectric/magnetic material is analyzed. A volume-surface integral equation (VSIE) approach is utilized to model the problem. By imposing the boundary conditions on the conducting surface, a surface magnetic field integral equation (MFIE) is developed. Inside the volume of the coating region, volume MFIEs are applied. The resultant integral equations are solved using the moment method. Numerical results for the bistatic radar cross section for different structures are presented. The results are validated using the exact series solution for a conducting circular cylinder coated with multilayers of homogeneous materials. Two types of coating materials are studied: the conventional or double positive (DPS) materials and the double negative (DNG) materials.

A surface integral equation formulation for electromagnetic scattering from a conducting cylinder coated with multilayers of homogeneous materials

A surface integral equation formulation is presented for electromagnetic scattering by a conducting cylinder coated with multilayers of homogeneous materials. Each layer may have a nonunity relative permittivity and permeability. Both the TM and TE polarizations are considered. The surface equivalence principle is utilized to model the problem where each layer is replaced by equivalent surface currents residing on the enclosing boundaries. A systematic procedure is developed to generate a set of coupled integral equations for an arbitrary number of layers. The method of moments is invoked to convert these equations into a sparse matrix equation which can be solved using sparse matrix routines. Numerical results are presented to demonstrate the accuracy and efficiency of the proposed method. The performance of the method is compared with that of the volume-surface integral equation formulation where a great saving in memory storage and computation time is achieved.

Theory of Polarization-Selective Coupling and Its Application to Design of Planar Orthomode Transducers

With the rapid and continuous development of new generations of wireless technologies and networks, exploring the underutilized millimeter-wave (mm-wave) band becomes inescapable. Polarization diversity has been an essential factor in the performance and capacity enhancement of various wireless systems including cellular networks. Accordingly, the design and development of dual-polarized antenna feeding structures in the mm-wave band is a must. In this paper, a compact wideband orthomode transducer design in the Ka-band is proposed and explored. The proposed architecture and design are based on a forward mode polarization-selective coupling strategy between two unconventional waveguides. These special waveguides are a combination between two types of guiding structure, namely, nonradiative dielectric waveguide and substrate-integrated waveguide. Polarization-selective coupling can be achieved in these structures due to different mechanisms by which orthogonally oriented modes are guided. Theoretical coupling levels of 0 dB are possible in the designed structure. Analytical analysis and design steps are given in detail. This analysis facilitates a complete control on the single-mode operation for each polarization. This control, besides the structure being planar, represents the main advantages of the proposed structure. Finally, a prototype is implemented and measured where an excellent agreement is achieved with the simulation results.

Characterization of substrate integrated non radiative dielectric slab waveguide for cross-polarized mm-wave components

Hybrid Substrate Integrated Non Radiative Dielectric Slab Waveguides are proposed as a new guiding structure suitable for mm-wave components. The proposed structure is a combination of two well-known guiding structures, each of which has its wide variety of applications but in different regimes of operation. The combination of the two guiding mechanisms in one physical structure gives unique characteristics to the resulting hybrid waveguide. A systematic analytical way is presented in this paper to characterize the new waveguide in terms of its dispersion relation, modes of operation, field solution, bandwidth of single mode operation, and power handling capability. Some possible applications and design recipes are discussed.