Estimation of dielectric constant of composite materials in buildings using reflected fields and PSO algorithm

This paper presents a free-space measurement technique for estimating the complex dielectric constant and loss tangent of the walls in given building. To determine propagation characteristics in buildings for wireless indoor communications, it is necessary to obtain the reflection and transmission properties of the building structures. The measurement of walls parameters need to be measured for each particular building. The free-space technique doesn´t need material samples and measurement can be made in specific building space. The single layered and multilayered models are included in presented models. The both polarizations are included. The main parts of the proposed measurement setup consist of Vector Network Analyzer (VNA) and two horn antennas. The measurement has been made in the existing building on non-destructive manner. The estimation of the complex dielectric constant from reflection and transmission coefficients is basically an optimization process because it is necessary to obtain good curve fitting between measured and calculated reflection coefficients for different angles of incidence for given material. In this particular case two methods are compared non-linear least squares method and Particle Swarm Optimization (PSO) method. The results obtained by PSO method show lower values of mean square error then with non-linear least squares method.