| dc.description.abstract | To set up an efficient wireless mobile communication system, it is necessary to characterize the environment and its components, in particular suitable antennas, and hence explore its RF requirements. Presented in this thesis are the results of investigations on these major aspects.
A ray?tracing?based site?specific modeling has been proposed for line?of?sight and out?of?sight propagation paths in rural and urban environments for a cellular structure. Computation of the received field strength with diffraction effects at the mobile has been carried out as a function of the distance of the mobile from the base station. The effect of variation of the height of the base station is also studied. The results show that the diffraction effects are pronounced. Also, base?station antenna height needs to be optimized for improved field strength.
As a requirement to handle large traffic density, microcellular structures are proposed. An efficient and fast algorithm for computation of field strength at the mobile in the microcellular environment is developed, taking into consideration the various possible reflections and diffractions. Multiple?image theory, Fermat抯 principle, and the Uniform Theory of Diffraction (UTD) have been incorporated in order to simulate the effect. This modeling technique is efficient compared to other modeling techniques reported in the literature, as it restricts the propagation paths to relevant ones, thereby effectively reducing the computation time for calculation of field strength at specific locations. The proposed model substantiates the measured values.
Effect of atmospheric attenuation on the path?loss characteristics in the above models has been computed. Polarisation effects on the propagation characteristics are also analysed. These analyses are carried out at 900 MHz, 1.956 GHz, 6 GHz, 11 GHz, and 60 GHz. It is inferred that higher microwave frequencies are strongly affected by heavy rain and are not suitable for large cells. Also, it is recommended that due to atmospheric gases and rain attenuation, 60 GHz can be used only for microcells and picocells.
An attempt has been made to replace the existing dipole of handheld portable telephones by microstrip antennas as a step toward miniaturised conformable antennas. The dipole pattern has been simulated using back?to?back appropriately designed microstrip patches. In order to minimise radiation hazard, a beam with a cone of silence towards the user抯 head is achieved by combining the different modes of two patch antennas.
Finally, some observations have been recorded regarding the improved characteristics of patch antennas for specific applications. A large bandwidth improvement is achieved by loading. Beam scanning using an optically driven substrate is also suggested. | |
