J. Litva

A dispersive boundary condition for microstrip component analysis using the FD-TD method

A dispersive absorbing boundary condition (DBC) which allows the dispersion characteristics of waves to be used as a criterion for designing absorbing boundary conditions is presented. Its absorbing quality is superior to that of the presently used Murs first-order boundary condition for microstrip component analysis, and its implementation is much simpler when compared to that of the super boundary condition treatment. Due to the significant performance improvement of the new boundary condition, the memory requirement can be reduced greatly when applying this boundary condition to microstrip component analysis. >

Accurate characterization of planar printed antennas using finite-difference time-domain method

The finite-difference-time-domain method (FD-TD) is used to characterize complex planar printed antennas with various feed structures, which include coaxial probe feed, microstrip line feed, and aperture coupled feed structures. A coaxial probe model is developed by using a three-dimensional FD-TD technique. This model is shown to be an efficient and accurate tool for modeling coaxial line fed structures. A novel use of a dispersive absorbing boundary condition is presented for a printed antenna with a high dielectric constant. All the numerical results obtained by the FD-TD method are compared with experimental results, and the comparison shows excellent agreement over a wide frequency band. >

A physical spatio-temporal model of multipath propagation channels

This paper presents a spatio-temporal model of multipath propagation channels based on a physically defined propagation process for testing and validation of the antenna array systems operating in multipath propagation environments. The idea behind the model is to generate a set of spatially distributed reflectors or scatterers which will act as sources for the signals arriving at the receiver in accordance with the distribution of excess delay times. The large scale and small scale signal fadings are incorporated into the model, which allows an easy and flexible simulation of multipath vector channels.

Fast finite-difference time-domain analysis of resonators using digital filtering and spectrum estimation techniques

The use of digital filtering and spectrum estimation techniques for improving the efficiency of the FD-TD algorithm in solving eigenvalue problems is discussed. The great improvement of the efficiency of the method is demonstrated by means of both numerical and measurement results. In addition, several improvements to the present FD-TD method for eigenvalue analysis are presented. These include the analysis of open dielectric resonators and the extraction of the resonant frequencies from the FD-TD results. The result for the open dielectric resonator analysis is validated using measured data. >

The use of fractals for modeling EM waves scattering from rough sea surface

A rough surface model based on fractal geometry is presented for the study of surface scattering. In particular, the Pierson-Moskowitz spectrum is incorporated into this model to represent a fully developed sea surface. The Kirchoff approximation is used to evaluate the scattered field from this rough surface. Some interconnection are found between the surface model developed and the statistical characteristics of the scattered field. These include: 1) the relationship between the surface correlation length and the surface fractal dimension; 2) the relationship between the shape parameter of the K-distribution and the surface fractal dimension; 3) the mean value of the scattered amplitude as a function of the surface fractal dimension; and 4) the effect of the incident angle on the scattered field.

A combined full-wave CG-FFT method for rigorous analysis of large microstrip antenna arrays

An accurate and efficient technique is presented for the analysis of large microstrip antenna arrays. The technique consists of an amalgamation of a spatially discrete scheme, consisting of the CG-FFT method and the complex discrete image (CDI) technique. The unique feature of this approach is the use of the spatially discrete CG-FFT for analyzing microstrip structures. The aliasing and truncation errors are thoroughly eliminated in this approach. In addition, the grad-div operators are transformed from singular Greens functions to differentiable expansion and testing functions by using Galerkins procedure, thereby improving the accuracy and the rate of convergence. To show the accuracy and efficiency of this technique, a number of microstrip arrays, including a large microstrip reflectarray, have been studied. It is found that the simulations carried out using this technique are in very good agreement with measurements.

Using linear and nonlinear predictors to improve the computational efficiency of the FD-TD algorithm

It is well known that the Finite-Difference Time-Domain (FD-TD) method requires long computation times for solving electromagnetic problems, especially for high-Q structures. The reason for this is because the algorithm is based on the leap-frog formula. In this paper, both linear and nonlinear predictors, which are widely used in signal processing, are introduced to reduce the computation time of the FD-TD algorithm. A short segment of an FD-TD record is used to train the predictor. As long as the predictor is set up properly, an accurate future realization can be obtained. We demonstrate, by means of numerical results, that the efficiency of the FD-TD method can be improved by up to 90%. With this result, the FD-TD algorithm becomes a much more attractive technique for solving electromagnetic problems. >

A new approach for estimating indoor radio propagation characteristics

Presents a new approach for estimating the propagation characteristics of indoor radio channels. The technique is based on the use of principal component analysis and the information theoretic criterion. It is shown, based on the simulation results, that the new technique can be used to overcome difficulties experienced by conventional methods and, as a result, is able to produce greater accuracy in its estimates of the channel parameters. The authors demonstrate the use of this technique by carrying out data analysis using measured indoor radio channel data. >

Radial basis function neural network for direction-of-arrivals estimation

The authors propose the use of a radial basis function (RBF) network for direction-of-arrival (DOA) estimation. The RBF network is used to approximate the functional relationship between sensor outputs and the direction of arrivals. Simulation results show that the new technique has a better performance in terms of estimation errors than the standard MUSIC algorithm.<<ETX>>

A new finite-difference time-domain algorithm for solving Maxwell's equations

An algorithm is presented for deriving finite-difference-time-domain (FD-TD) solutions of Maxwells equations. When compared with Yees method (1966), it is found that the stability conditions for this method exceed those of Yees method by the factors 1.41 and 1.73, respectively, for the two-dimensional and three-dimensional cases. The algorithm is compatible with both Yees method and the finite-element-time domain method, thereby allowing for unification of the two. The algorithm will also provide greater flexibility in formulating and studying the multigrid method, the variable mesh method, and the method of finite difference approximations of the boundary conditions.<<ETX>>