Kazem F. Sabet

A hybrid MoM/FDTD approach for an efficient modelling of complex antennas on mobile platforms

The use of a hybrid Method of Moments (MoM)/Finite Difference Time Domain (FDTD) method can be effective for solutions of electromagnetic propagation problems, which are intractable for single numerical methods. This paper presents a rigorous, hybrid full-wave analysis of effects pertinent to vehicular multi-antenna system performance for wireless communication applications. For a fast solution of such complex electromagnetic problems essential for an efficient design and optimization of high performance antennas under the influence of mobile platforms, MPI-based parallelization strategies are developed. Applications where the combined MoM/FDTD simulation of wire antennas mounted on a vehicle sheds light into the impact on the antenna performance are provided.

Compact wireless antennas using an artificial dielectric lens

This paper presents a novel design for compact multifunction antennas for wireless applications. To reduce the physical size of the antenna, a high permittivity substrate or superstrate is utilized. In order to suppress the surface waves in the dielectric slab, a grading of the index profile is proposed in both axial and radial directions. Furthermore, the index grading can be done in the antenna feed area to achieve impedance matching. A low-cost and easy-to-manufacture way of achieving the graded index profile is proposed, whereby a set of air voids are created inside the dielectric material to realize an effective dielectric constant. Extensive simulation and experimental results are presented for a slot ring antenna with a high permittivity dielectric superstrate lens.

Compact wireless antennas using a superstrate dielectric lens

Todays vehicles have been transformed into sophisticated platforms for transmission and reception of a wide spectrum of electromagnetic waves. These include the traditional AM/FM radio, personal communication services (PCS) like cellular phone and pager systems, remote feature access (RFA) like keyless entry, navigation systems using GPS, and direct satellite radio broadcast. The transmission and reception of electromagnetic waves out of and into the vehicle is conducted through a multitude of vehicular antennas usually in the form of metallic rods protruding out of the vehicles body. In commercial vehicles, protruding antennas impose aesthetic and mechanical problems and are exposed to vandalism. In military vehicles, they aggravate radar visibility and reduce survivability. This paper is concerned with the development of compact wireless antennas with high radiation efficiency, which offer the capability of multifunction performance on a common platform.

An accelerated hybrid genetic algorithm for optimization of electromagnetic structures

This paper presents a novel optimization technique that combines classical and statistical methods in an innovative and efficient way. In specific, an evolutionary genetic algorithm (GA) has been developed that utilizes a local minimization scheme based on the method of conjugate directions. The proposed optimizer has been applied to the design of planar microwave circuits and printed antenna arrays. The advantages of the proposed technique are illustrated by ample numerical results.

Numerical simulation of scattering from rough surfaces: a wavelet-based approach

Haar and B-spline wavelet basis functions are applied to the method of moments (MoM) in order to speed up the Monte Carlo simulation of scattering from rough surfaces. Application of wavelet basis functions in conjunction with imposed threshold levels produce sparse impedance matrices which are then solved efficiently using search routines such as the conjugate gradient method. These different threshold levels are imposed on matrix element values with respect to the element of largest magnitude in order to determine the accuracy versus computing speed criterion. Results are compared to previous results computed using a conventional pulse basis function and point matching as well as the existing theoretical solutions for rough surfaces. It is shown that wavelet basis functions provide substantial reductions in both memory requirements and computation time while providing very accurate results.

A study of dielectric resonators based on two-dimensional fast wavelet algorithm

This letter reports the implementation of orthonormal wavelets for the moment method characterization of three-dimensional dielectric structures. The formulation is based on a 3-D volume integral equation, which is solved numerically using a 2-D multiresolution analysis in conjunction with a sub-domain pulse basis. The use of multiresolution expansions leads to highly sparse linear systems that can be solved very efficiently using the bi-conjugate gradient method. To speed up the numerical evaluation of moment integrals, the fast wavelet algorithm (FWA) has been employed.

K and Ka-Band silicon micromachined evanescent mode resonators

High-Q silicon micro ma chined evanescent-mode resonators for K and Ka-band are investigated. Such structures can be realized by loading a below the cut-off waveguide cavity with capacitive posts and can easily be combined to form multi- pole filters. The capacitive post placed inside the cavity lowers its resonant frequency. Therefore, compared to a resonant cavity, the size of the evanescent cavity is dramatically reduced, while still achieving the same resonant frequency. The loss also increases, but relatively high unloaded quality factor can be maintained. Design methods with full-wave analysis and circuit-modeling results are presented. Experimental results for K and Ka-band resonators are also presented.

A hybrid-statistical approach for accurate characterization of MEMS on complex platforms

Micro-electromechanical systems (MEMS) are used in a diverse group of fields. In this paper, we are concerned with the communication and sensing applications, particularly in connection with the Reconfigurable Aperture Antenna (RECAP) project. We present a finite element method (FEM)-based approach to characterizing MEMS devices in the presence of radiators. We concentrate on modeling the MEMS switches since this problem has its own challenges. By modeling, we mean extracting a lumped element model consisting of resistors, inductors and capacitors.

Manufacturable wafer-scale microstrip patch antennas

The antenna bandwidth depends on the thickness of the Si wafer on which it is fabricated. Unfortunately, increasing the thickness of the substrate, results in more power leaking to substrate modes and surface waves, therefore the efficiency of the antenna is reduced. By using deep-reactive- ion-etching (DRIE) the Si underneath the patch antennas can be very accurately etched, in order to form cavities with specific size and depth. However, achieving a uniform etch depth on multiple backside cavities located along a 4-inch wafer is challenging. As will be shown in the subsequent section even minor non-uniformities in the cavities depth can significantly de-tune the patch antennas and thus deteriorate the array performance. This paper presents a successful effort to improve the DRIE uniformity along a 4-inch Si wafer, and demonstrates consistent antenna performances.

A hybrid approach for modeling complex antenna systems on vehicular platforms

The use of multi-antenna systems on vehicular platforms, for the implementation of ad-hoc wireless network architectures, is typically hampered by the problem of co-site interference between transceivers loading neighboring radiating elements and the impact of the platform on the radiation pattern. This paper presents a rigorous, full-wave analysis of effects pertinent to vehicular multi-antenna system performance, based on a hybrid time/frequency domain analysis that combines the method of moments (MoM) with the finite difference time-domain method (FDTD). For the fast solution of such problems, MPI-based parallelization strategies are developed. Applications where the combined MoM and FDTD simulation of multi-antenna systems sheds light on the serious impact of mutual transceiver interference on wireless network operation are provided.