Antonio José Martins Soares

Optimization of gain, impedance and bandwidth in Yagi-Uda antennas using genetic algorithm

A new application for genetic algorithms (GA) is introduced. After the use of this kind of algorithm in electromagnetic problems, especially those related with antennas, the present work proposes bandwidth optimization in Yagi-Uda antennas. In design of an antenna, there is more then one parameter that must be fit. Gain is just one of them, but impedance and bandwidth must also be fit. That is the main reason why a GA is often chosen; it can optimize more then one parameter at the same time and, as a stochastic method, it will not be stuck in a local minimum.

Simplified Characterization of the Urban Propagation Environment for Path Loss Calculation

This letter presents a study to characterize the urban environment in a simplified way in order to predict the power level received in mobile communication systems. The proposed method considers the morphology of the environment as a function of area occupied by buildings. The method was developed based on field measurement data obtained in Munich, Germany, and validated through comparisons with experimental tests performed in Ottawa, Canada, and Rosslyn, VA.

A New Procedure for Assessing the Sensitivity of Antennas Using the Unscented Transform

In this communication, we introduce a new procedure to analyze the sensitivity of antennas. The procedure is based on the method of unscented transform (UT) developed by Julier and Uhlman in 1997. Although the UT is used in control engineering, the method has only recently been applied to electromagnetic (EM) problems. This work describes the application of the UT both for single and multiple random variables cases. The UT method is applied to problems using examples involving different types of antennas. In each example, the UT method is combined with different numerical methods to perform the sensitivity analysis of wire or reflector antennas. In the first example, the results were validated with results from the Monte Carlo technique. The second example investigated the convergence of the UT procedure, and the final example compared UT results with measured data. The main conclusion is that UT is a feasible alternative to the popular Monte Carlo technique, with the advantage of being far less computationally expensive.

Determination of Measurement Points in Urban Environments for Assessment of Maximum Exposure to EMF Associated with a Base Station

A base station (BS) antenna operates in accordance with the established exposure limits if the values of electromagnetic fields (EMF) measured in points of maximum exposure are below these limits. In the case of BS in open areas, the maximum exposure to EMF probably occurs in the antenna’s boresight direction, from a few tens to a few hundred meters away. This is not a typical scenery for urban environments. However, in the line of sight (LOS) situation, the region of maximum exposure can still be analytically estimated with good results. This paper presents a methodology for the choice of measurement points in urban areas in order to assess compliance with the limits for exposure to EMF.

Estimating the Location of Maximum Exposure to Electromagnetic Fields Associated with a Radiocommunication Station

This paper proposes an approach to estimate the probable location of maximum exposure to electromagnetic fields associated with a radiocommunication station, based only on information of antennas height, half-power angle and tilt. This approach can be implemented when simulation tools are absent, or/and few basic information on radiating system is available. The proposed analytical expression is compared with simulated and real measured data, showing the good accuracy of the proposed technique. The focus of the work are base stations, however the results may be applicable to any radiocommunication station. As far as the authors know, this is the first study to present a mathematical formulation in closed form under the considered constraints.

Analysis of the perturbation's size and the feeding topology on the dual-mode resonator in microstrip structure using FDTD

The dual-mode resonators have characteristics that make them highly attractive for use in wireless and mobile communications systems. In this work, the method of the finite differences time domain (FDTD) is used to analyze the behavior of the structure type according to the variation of the perturbations size and to the kind of the topology feeding.

Software Architecture for the Design of Electromagnetic Simulators [EM Programmer's Notebook]

A software architecture for the design of electromagnetic simulators is presented. It is suggested that the system should be structured in layers, due to the benefits of separating responsibilities, facilitating the software adaptation to consider different environments. Using this architecture, new features can be easily added to the software at low cost. An application using the proposed architecture was developed with the Finite-Difference Time-Domain (FDTD) Method, but it allows different numerical methods to be implemented.

A surgical device for radiofrequency ablation of large liver tumors.

Radiofrequency ablation has become an accepted treatment option of patients with primary and metastatic liver tumors. We propose an ablation electrode array consisting of 4-8 blade shaped electrodes arranged in a circular geometry for the treatment of large liver tumors. We developed a 3D code based on the finite difference method for evaluating the effect of different numbers of electrodes (4, 6 and 8) and electrode distance on lesion size. The configuration with six electrodes can ablate a volume of 70 x 70 x 40 mm(3) in approximately 5 min, with tissue temperature above 50 degrees C throughout the treatment volume. We then performed an experimental study in polyacrylamide gel in order to validate the theoretical results. The average temperature error between the simulation and the experiment was 3.8% at the center of the electrode array. This study shows that the proposed device potentially allows more rapid treatment of large tumors than current radiofrequency ablation devices.

Side lobes from radio base station antenna in the evaluation of human exposure to EMF

Maximum human exposure to electromagnetic field associated to a base station is, usually, due to the main lobe of the antenna and is located in the range of some tens to a few hundred meters from its mast. In this paper, we discuss practical situations in which the side lobes of the antenna is responsible for the maximum exposure in distances closer to the base station, even transporting less energy than the main lobe. It will also be presented guidelines to estimate what portions of the pattern of the antenna contributes to the highest field strength. This guidance may be used when few radiating system information is available, like gain, height, tilt and vertical half-power angle, and side lobe level.

Measurements of a CW signal in Brazil and comparison with prediction using ITU-R P.1546-1

This paper compares the prediction given by ITU-R P.1546-1 to measurements obtained using a CW maintenance signal of a trunking system repeater operating at 856 MHz in the Brasilia, capital of Brazil.