JultikaUniversity of Oulu repository

Abstract

Radio waves interact differently with different materials. The knowledge of reflection and transmission characteristics of the electromagnetic waves through and from the building walls is the key in designing a radio propagation model. The dielectric properties of the material determine the behavior of reflection and transmission of the electromagnetic waves. Therefore, an oblique reflection model is implemented in this thesis to estimate the dielectric properties of various walls at frequency range of 0.7–7 GHz (6.3 GHz bandwidth). The measurement setup consists of a four-port vector network analyzer, two wideband dual-polarized cross-shaped Vivaldi antennas and two 8 m long coaxial cables. Measurements for parallel and perpendicular polarizations are achieved simultaneously by using the dual-polarized antennas. Time-domain gating is applied to separate the desired reflection and eliminate all other multiple reflections from the environment and to suppress the Line-of-Sight component from the delayed response.

The estimation of dielectric property of a material is an optimization problem where a suitable objective function is minimized to get the appropriate value. A theoretical model is implemented, so that the minimum difference between the theoretical and measured absolute value of reflection coefficient gives an estimated value of complex relative permittivity. The non-linear least squares algorithm is used for optimization purpose. The real and imaginary part of complex relative permittivity is investigated in this thesis. The real part signifies the amount of electric energy stored in a material, and is called dielectric constant whereas the imaginary part is called the loss factor, which signifies the dissipation of the radiated energy. The estimated values are in good agreement with the values found in the literature. The estimated dielectric properties in this study, such as dielectric constant, loss tangent and Brewster angle of the various materials can be utilized further in designing radio propagation models for similar environments.