For the modeling of multipath propagation in every wireless systems, the ray tracing method has been widely studied. However, large errors may result due to the approximation of geometrical optics in curved surfaces. This paper therefore focused on the curved surfaces and edges, which are difficult to handle in ray tracing. Examples of curved surfaces can be found in arched cross-section tunnels which are common in highway networks of mountainous areas. The traditional ray tracing method of dividing the curved surface into smaller flat plates is not so accurate as the size of smaller plates may not satisfy the geometrical optics assumption, and the reflection point which satisfies Fermat's principle may not exist. In this work, a new ray tracing method is proposed with 2 contributions. The first one is the implementation of the reflection coefficient for curved surfaces in ray tracing. The second is applying the physical optics method on the caustics region. To evaluate these methods, path gain simulation results for an arched cross-section model are compared with measurements made inside an arched tunnel. To further improve the simulation results, the effect of rough surface is introduced, and the results are again compared with measurement.

In order to realize a higher density version of the conventional optical disk, shorter wavelength laser and narrower track pitch have been put to practical use. However, using narrow track pitch can cause the increase of the crosstalk from the adjacent tracks. Moreover, the use of narrow pitch and short wavelength can also give rise to the increase of deterioration of the detected signal characteristics due to the microscopic roughness of disk surface. In this paper, in order to estimate the effect of surface roughness theoretically, we try to analyze the light-beam scattering and detected signal characteristics of a blue laser optical disk model with random rough surfaces by the Finite Difference Time Domain (FDTD) method.

A program is developed to simulate the signal received by a bistatic pulse radar for a defined scenario. The signal collected at the receiving antenna is calculated as a function of time by taking into account the vectorial aspect of the electromagnetic waves and various elements operating in the radar radiolink. The radar radiolink is designed in a modular structure for a general configuration where the transmitter, the target and the receiver are moving. Modules such as elements characterizing the antennas radiation or defining the target scattering can be inserted in accordance with the desired radar scenario. Then the developed model permits to simulate a wide range of radar scenarios where returns from targets and clutter can be individually processed and their characteristics can be investigated in time or frequency. The interest of this model is great because it permits, for a defined scenario, to generate radar data which can be used in signal processing algorithms for target detection, clutter suppression or target classification. This paper shows the implementation of the simulation program considering a concrete radar scenario. The presented scenario deals with the simulation of the sea clutter occurring in a bistatic radar radiolink over the sea surface. In this application where the sea surface is considered as the target, the electric field scattered from the sea surface is calculated by assuming that the surface is described by two independent scales of roughness.

In this paper we report the results of a study regarding the backscattering from wind-roughened water surfaces. The reference profile data has been deducted by an experiment held at the University of Heidelberg circular wave tank facility. The scattering theory is based on a fractal description of the surface and a combined use of the Kirchhoff approximation and the small perturbation method (SPM). The scattering results are tested versus the ones obtained via the periodic-surface moment method. The study shows the reliability of the novel approach.