Ezzeldin A. Soliman

Dual-polarized omnidirectional planar slot antenna for WLAN applications

A novel planar slot antenna is presented in this paper. The antenna provides dual-polarization and omnidirectional radiation patterns. Hence, it is suitable for hand-held equipments of wireless systems. The proposed antenna is optimized for operation at 5.2 GHz. The antenna, without ground plane extension, occupies an area of 2.17/spl times/2.17 cm/sup 2/. An impedance bandwidth of 10.6% is obtained, with a very good isolation between the two excitation ports. Appealing omnidirectional radiation patterns are maintained over the entire impedance bandwidth. The gains of the two polarizations are 2.59 and 3.52 dB, while the radiation efficiencies are 93% and 99.8%.

Accelerated gradient based optimization using adjoint sensitivities

An electromagnetic feasible adjoint sensitivity technique (EM-FAST) has been proposed recently for use with frequency-domain solvers . It makes the implementation of the adjoint variable approach to design sensitivity analysis straightforward while preserving the accuracy at a level comparable to that of the exact sensitivities. The overhead computations associated with the estimation of the sensitivities in addition to the system analysis are due largely to the calculation of the derivatives of the system matrix. Here, we describe the integration of the EM-FAST with two methods for accelerated estimation of these derivatives: the boundary-layer concept and the Broyden update. We show that the Broyden update approach (Broyden-FAST) leads to an algorithm whose efficiency is problem independent and allows the computation of the response and its gradient through a single system analysis with practically no overhead. Both approaches are illustrated through the design of simple antennas using method of moments solvers.

Neural networks-method of moments (NN-MoM) for the efficient filling of the coupling matrix

In this paper, novel radial basis function-neural network (RBF-NN) models are presented for the efficient filling of the coupling matrix of the method of moments (MoM). Two RBF-NNs are trained to calculate the majority of elements in the coupling matrix. The rest of elements are calculated using the conventional MoM, hence the technique is referred to as neural network-method of moments (NN-MoM). The proposed NN-MoM is applied to the analysis of a number of microstrip patch antenna arrays. The results show that NN-MoM is both accurate and fast. The proposed technique is general and it is convenient to integrate with MoM planar solvers.

Propagation of Electromagnetic Waves in Planar Bounded Plasma Region

This paper aims at developing a technique to calculate the reflection, absorption, and transmission of electromagnetic waves by a bounded plasma region. The model chosen for this study is a magnetized, steady-state, two-dimensional, nonuniform plasma slab, which is presented by a number of parallel flat layers. It is assumed that the electron density is constant in each layer such that the overall electron density profile across the slab follows any prescribed distribution function. The proposed technique is referred to as Scattering Matrix Model (SMM). The fields in each layer are written in the form of summation of the appropriate eigen functions weighted by unknown scattering coefficients. These coefficients are determined via the application of the appropriate boundary conditions at each interface. The effect of varying the wave frequency and the plasma parameters on the reflected, transmitted, and absorbed powers are presented and discussed.

Optimization and Characterization of Electromagnetically Coupled Patch Antennas using RBF Neural Networks

A new neural network model is presented in this paper. It utilizes radial basis functions neural network. The model solves the problem of the electromagnetically coupled microstrip patch antennas. At a specific resonance frequency, the proposed model predicts the optimum geometrical dimensions of both the patch and feeding microstrip line. Moreover, it provides the important characteristics of the optimum design. These characteristics include the impedance bandwidth, gain, and radiation efficiency. The proposed neural network model is very accurate and extremely faster than the classical approach.

Theoretical Study of Metal-Insulator-Metal Tunneling Diode Figures of Merit

The performance of metal-insulator-metal (MIM) diodes is investigated. In this paper, we derive an analytical model that uses the Transfer Matrix Method based on the Airy Functions (AF-TMM) for the tunneling transmission probability through any number of insulating layers. The fast-computing AF-TMM simulator results show a complete matching with the numerical Non-Equilibrium Greens Function and a reasonable matching with previously published experimental results. This study shows the effect of the work function difference and insulator thickness on MIM diode performance. The advantage of using two insulator layers on enhancing the diode responsivity, resistance, and nonlinearity is also investigated.

An adjoint variable method for sensitivity calculations of multiport devices

Recently, an adjoint variable method (AVM) for sensitivity calculations has been proposed for use with the method of moments solvers. In this paper, we extend this method to be suitable for application to multiport devices. The target objective function is usually represented in terms of the devices S-parameters. Our AVM obtains the sensitivities of the S-parameters with respect to all design variables using only one full simulation with additional overhead. This overhead is usually less than the computation time of a full simulation. An analytical expression for the adjoint excitation is derived, leading to stable sensitivities. The potential of the proposed technique is demonstrated by analyzing low-pass and bandpass filters. The results show very good agreement between the proposed AVM and the conventional finite-difference approach (FDA). Moreover, the AVM is always faster than the FDA. The speed-up factor increases as the size of the problem increases.

Antenna arrays in MCM-D technology fed by coplanar CPW networks

In this paper, the design, fabrication, and characterization of planar antenna arrays in the MCM-D technology are presented. The arrays are fed by coplanar feeding networks built using coplanar-waveguide lines. 2/spl times/2 and 4/spl times/4 arrays of slot dipoles designed to work in K-band, around 25 GHz, are also presented. The analysis was carried out both theoretically and experimentally. The results include the return loss, radiation patterns, and antenna gain. The proposed arrays are compatible with the driving electronics technology, enjoying high-impedance bandwidth, low cross polarization, high gain, and high radiation efficiency.

Full-wave analysis of multiconductor multislot planar guiding structures in layered media

In this paper, a generalized two-dimensional formulation for solving planar guiding structures is presented. The formulation is capable of analyzing guiding structures consisting of an arbitrary number of slots and strips with arbitrary width, thickness, and conductivity in a full-wave regime. Integral equations solved with the method of moments in the spatial domain are used in the analysis. All information related to the fundamental modes of the guiding structure are available from the presented theory. This information includes (for each mode) the propagation constant, electric and magnetic current distribution, modal power, and the characteristic impedance. Numerical results for a number of planar guiding structures are presented, which validate the proposed theoretical formulation.

The Ellipsoidal Technique for Design Centering of Microwave Circuits Exploiting Space-Mapping Interpolating Surrogates

A new technique for design centering of microwave circuits is introduced. This technique exploits the space-mapping interpolating surrogate (SMIS) with a modified ellipsoidal technique. The design centering solution for microwave circuits is obtained with a small number of fine model evaluations and, hence, the number of electromagnetic simulations is greatly reduced. Practical and demonstrative examples are included to show the efficiency of the new technique