Cássio G. Rego

Efficient Ray Tracing for Radio Channel Characterization of Urban Scenarios

This paper presents an efficient ray tracing algorithm for the use of the uniform theory of diffraction (UTD) in radio channel characterizations of urban environments. The algorithm is based on a 2-D image theory, which is properly modified to yield 3-D ray trajectories. Multiple reflections and diffractions are considered through the classification of multipath components into four different categories. The adoption of such ray classes eliminates redundant calculations throughout the ray-tracing process, improving the analysis of the electromagnetic propagation over the coverage area

Novel Heuristic UTD Coefficients for the Characterization of Radio Channels

This work presents a novel heuristic coefficient for the uniform theory of diffraction, suited to characterize radio channels. The new coefficient combines features from two previously proposed heuristic coefficients. The diffraction by a conducting wedge is investigated in order to demonstrate the usefulness of the proposed coefficient

A High-Order Unconditionally Stable FDTD-Based Propagation Method

This letter introduces a finite-difference time-domain (FDTD) propagation method employing a moving window algorithm and a new formulation based on three features: high-order and unconditionally stable method with a material independent perfect matched layer (PML) formulation. The achievement is an efficient and accurate time-domain (multiband) propagation method. The formulation is validated through an analytic problem. Finally, we analyze two measurement campaigns with HF and VHF signals to evaluate the performance of method.

A Time-Domain Uniform Asymptotic Theory Applied to the Analysis of Pulse-Excited PEC Wedges

In this letter, a time-domain version of the uniform asymptotic theory of diffraction, henceforth named TD-UAT, is introduced and is employed to obtain the fields scattered by a perfectly electrically conducting wedge illuminated by an arbitrarily oriented electric dipole. The results of TD-UAT are compared to those obtained from an implementation of the time-domain uniform theory of diffraction (TD-UTD), and its applicability is demonstrated.

Unified characterization of UWB antennas in time and frequency domains: an approach based on the singularity expansion method

In this work, an approach based on the Singularity Expansion Method [1] is employed to obtain a semi-analytical representation for the effective length operator and a transfer function of UWB antennas. This operator can be employed in the calculation of some important parameters related to UWB antennas, such as the gain operator and the time-independent radiation pattern, allowing an unified characterization of antennas in time and frequency domains. Some preliminary results of the construction of impulsional induced currents, from which the effective length operators can be derived, are presented for antennas comprising thin wires.

Time-domain analysis of a reflector antenna illuminated by a Gaussian pulse

In this work the asymptotic Time-Domain Physical Optics and the Time-Domain Uniform Theory of Diffraction are applied to the analysis of a hyperboloidal reflector antenna illuminated by a Gaussian pulse to illustrate their applicability. The results are compared with those obtained by a reference integral-equation formulation, in order to specify the limitations of the time-domain formulations.

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.

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.

Improved High-Order FDTD Parallel Propagator for Realistic Urban Scenarios and Atmospheric Conditions

This letter introduces an improved finite-difference time-domain (FDTD) propagator for radiowave prediction in complex urban environments. The original method was based on an unconditionally stable scheme with a high-order formulation and material-independent perfectly matched layers in a moving window algorithm (US-HO-MI-MW-FDTD). In the present work, the regularization technique is applied to treat material discontinuities and consequently to improve the accuracy of the high-order formulation. This permits the inclusion of urban buildings on the FDTD analysis. Moreover, the original algorithm is parallelized with the OpenMP library to achieve high computation performance and use finer FDTD meshes. The new propagator is validated through cases involving atmospheric refraction. Finally, we present and analyze a cellular system measurement campaign.