Antennas for smart radio systems at micro- and millimeter-wave frequencies 

During the last years the demand for high data rate mobile communications is permanently increasing. High capacity radio systems with better coverage, high transmission quality and more efficient use of the radio spectrum are required. The need for the new radio systems drives developments in millimeter-wave frequencies. Smart radio systems, which can be a good option to improve the system's capacity, comprise several research areas such as antenna design, signal processing algorithms, channel modelling and coding. In this thesis, micro-and millimeter-wave antenna designs, scattering properties of different surfaces, and radio wave propagation modelling in indoor environments are studied. The first part of the work deals with antennas and starts with the characterization of a printed inkjet monopole antenna on different metallic platforms. The information obtained during measurements shows that the realized gain of the antenna can be increased if the antenna is disposed on a metallic platform. This peculiarity can be used in millimeter-wave identification systems. In this work the performance of reconfigurable fluidic and conformal antennas are studied. The size and shape of liquid metal radiating element can be changed in order to modify the directional pattern of the antennas. Conformal antennas with a beam switching network can be used to improve the system capacity. In the second part of the thesis radio wave propagation at millimeter-wave frequencies was studied. In this work empirical characterization of scattering patterns of two built surfaces, i.e. brick and glass wall, was done. This information can be utilized in geometry-based channel modelling. In addition, we performed ray tracing simulations with the antenna structures developed in the first part of the thesis, in a conference room scenario to estimate optimum antenna configuration. To evaluate realistic conditions of radio wave propagation in indoor environments, human shadowing was also considered. It was shown that the preliminary information about radio wave propagation in the defined scenario can be obtained by performing ray tracing simulations and realistic antenna configurations can be replaced with Gaussian shaped antenna patterns before final antenna design development.