Glaucio L. Ramos

Propagation measurements of a 3.5 GHz signal: path-loss and variability studies

The results of propagation measurements of a 3.5 GHz signal realized on a typical urban environment at Rio de Janeiro city are presented. The path-loss, obtained from two different urban environments, is calculated and compared with the most popular prediction models in the literature. Variability characteristics such as the large-scale fading and small scale fading of the envelope of a received signal are estimated from some known probability functions. The obtained statistics together with other such the level crossing rate (LCR) and average fade duration (AFD) formulations are also compared with the results obtained from the measurement data.

Parallel Implementation of a Combined Moment Expansion and Spherical-Multipole Time-Domain Near-Field to Far-Field Transformation

A time-domain spherical-multipole near-to-far-field algorithm running in a parallelized code version is introduced in this paper. Such an approach is employed to obtain UWB antenna radiated fields and radiation patterns directly in time domain, which is more convenient to perform a unified characterization in time and frequency domains. We propose the use of the OpenMP, an application program interface that permits the code parallelization with almost no intervention. The results show that the proposed technique allows a code running 28 times faster when using a computer with 24 processors, each one with two threads, when compared with the sequential one. It also suggested a moment expansion technique to improve the accuracy and computational efficiency when using Gaussian pulse excitation when compared with the Fourier transform.

Characterization of the radiation pattern of antennas via FDTD and time-domain moment expansion

An alternative method is proposed to characterize the radiation pattern of antennas from an impulse response, based on a moment expansion together with a frequency domain near-to-far-field transformation via a FDTD/CPML solver. The approach introduced in the present work is intended for printed antenna analysis in special cases when the geometries to be modeled require a high degree of discretization in the space-time domain, which directly affects the frequency resolution when using FFT to perform the conventional NF-FF techniques. Results are compared with those obtained by a reference frequency-domain NF-FF technique and the applicability of the proposed method is demonstrated.

Moment expansion and nonuniform FFT applied to antenna reflection parameter characterization using a FDTD/WP-PML algorithm

This paper presents the results of the application of a moment expansion and a nonuniform FFT technique together with a FDTD algorithm in order to determinate the return loss parameter of printed antennas. The impedance characterization of wideband printed antennas with lossy substrates is introduced by means of an approach based on FDTD method and the WP-PML absorbing boundary condition. It was used a simple voltage source model where an excitation plane with an Gaussian vertical electrical field was imposed to a rectangular area just below the structure to be analyzed. Results obtained for the return loss of a multiband and an UWB printed antenna are compared to those determined from conventional FFT based methods available in the scientific literature as well as measurements previously done, in order to show the applicability of the methodology that has been developed herein. The results obtained for return loss parameter showed good agreements between the techniques proposed by this work and the results previous done.

Multi-band printed antennas impedance characterization using a FDTD/WP-PML based methodology

This paper presents the results of the application of a FDTD technique to determinate the return loss parameter of two printed multi-band antennas. The impedance characterization of wide-band printed antennas with lossy substrates is introduced by means of an approach based on FDTD method and the WP-PML absorbing boundary condition. It was used a simple voltage source model where an excitation plane with an Gaussian vertical electrical field was imposed to a rectangular area just below the structure to be analyzed. Preliminary results obtained for the return loss of MIMO multi-band antennas are compared to those determined from other FDTD-based methods available in the scientific literature in order to show the applicability of the methodology that has been developed herein. The results obtained for return loss parameter showed good agreements between the technique proposed by this work and the results previous done.

18 GHz propagation measurements and analysis in Belo Horizonte/Brazil

This paper presents a 18 GHz cm-Wave measurement-based campaign and path-loss analysis and a comparison with the traditional Alpha-Beta (AB) and the Close-in (CI) propagation models. A suburban scenario in the city of Belo Horizonte, Minas Gerais, Brazil, was considered and measurements were done considering LOS and NLOS conditions. The recorded samples data were processed and an outdoor propagation path loss was obtained, and then fitted in a curve to compare with the reference propagation models. It was observed a path loss exponent of 4.737 for the AB model, an exponent of 2.923 and 2.472 for the CI model with reference distances of 1 m and 2.5 m, respectively. A Beam Combining Gain (BCG) analysis was also performed and a mean value of 3.4 dB was obtained when using the 3 strongest components of two measurement points.

An improved Bi-Yagi antenna through metamaterial technology

In this paper Capacitively-Loaded Loop (CLL) metamaterial structures are applied to a Bi-Yagi antenna in order to improve its overall performance. Preliminary results show that the new antenna can be designed with an improvement of 13.48 dB on the reflection parameter, 0.37 dB on the gain, followed by a reduction of 11% on its area, when compared to the conventional Bi-Yagi antenna found in the literature.

FDTD near field data reduction using principal component analysis

A time domain spherical multipole near-to-far-field algorithm running together with a principal component analysis (PCA) signal processing technique is introduced in this paper. Such approach is employed to reduce the near fields obtained by a finite-difference time-domain (FDTD) code that will be used as input to a spherical multipole near-to-far-field transformation algorithm. The technique is applied to obtain the radiation pattern of a half-wavelength dipole, thus validating the code, and also for a configuration of two array dipole. Preliminary results show that when we compare the original signal with the reconstructed using a threshold value of 0.1 the required near-field data is reduced by an average value of 83% for the half-wavelength dipole and also shown that even if the technique is more sensitive in the presence of lobes it can significantly reduce the near-field components.

Characterization of the radiation pattern of antennas using time-domain spherical-multipole and moment expansion

This paper presents results of a time-domain spherical-multipole near-to-far-field transformation together with a moment expansion applied to antenna radiation patterns. The equivalence principle is applied to the tangential fields all over the FDTD/WP-PML spatial grid and the use of the spherical-multipole expansion leads to the near-to-far-field transformation, and energy and power norms of temporal signals are used to obtain the antenna radiation patterns for transient and steady-state responses. Such approach is employed to obtain UWB antenna radiated fields and radiation patterns directly in time-domain, it being more convenient to perform an unified characterization in time and frequency domains.

Caracterização Morfológica Utilizando Imagens de Satélites

Este artigo apresenta uma tecnica de caracterizacao morfologica utilizando imagens de satelites. A caracterizacao morfologica possibilita mapear os recursos naturais de uma regiao. Imagens digitalizadas provenientes do sensor ETM+ do satelite Landsat-7 foram utilizadas e geoprocessadas pelo software Spring. O geoprocessamento foi realizado em quatro etapas: georeferenciamento, composicao das bandas, segmentacao e classificacao. Foi realizado o mapeamento morfologico da regiao de Foz do Iguacu – PR. A tecnica utilizada apresentou resultados satisfatorios no que concerne a exatidao e a qualidade das imagens.