Measurements and modelling of reflection and transmission from smooth and rough surfaces at 62 GHz
Mobile communication often suffers from interference caused mostly by multipath propagation mode. This latter is associated with signal delays and signal level fades due to reflections, scatters, transmissions and diffractions by obstacles surrounding the environment. Indoor and outdoor building layout often influence the signal. In order to understand and mitigate the signal decay, knowing the internal properties as well as the surface characteristics of building materials could improve the deterioration of the signal. This thesis presents a study on the characterisation of the internal properties and the surface of various building materials at 62.4 GHz. Models have been applied to help in the interpretation of the reflectivity, scatter and transmissivity measurements performed on different materials. Reflectivity and transmissivity measurements at 62.4 GHz have been made inside the anechoic chamber on eight different building materials, and results are expressed as functions of observation and incident angles. It has been shown that the well-known Fresnel coefficients fail to predict reflectivity and transmissivity values when the thickness of the material is not too large compared to a wavelength. A model based on multiple successive internal reflection has been developed and successfully used to explain experimental results. The effects of this reflection mechanism on changing the statistics of an indoor mobile radio channel has also been demonstrated using raytracing. The model has also been utilised to provide estimates of the dielectric parameters of building materials. Measurements of the scattered field from rough surfaces have also been presented. Purpose made rough surfaces have been constructed by impregnating concrete slabs by 10, 20 and 40 mm angular stones. Two building facades one made from big stone and the other being pebble-dash have also been measured. The parameters describing the surface roughness have been measured and used to calculate, using the Kirchhoff approximation, the scatter level. It has been shown that the scattered field is of, a diffuse and random nature. Predictions have been found to underestimate the scatter level. Further measurements have been made to quantify the amount of depolarisation by rough surfaces and examine any possible correlation with the values of the parameters describing the rough surface. It has not been possible to relate depolarization and roughness. In order to understand the reflection off rough and smooth surfaces, co and cross-polarisation measurements were made inside the anechoic chamber on surfaces made from smooth and rough parts. The semi-specular level has been found to vary with the percentage of rough surface area within the intersection area made from the transmit and receive antennas. This level has been successfully predicted by combining experimental results made on all smooth and all rough slabs by the percentage of their area within the total cross-intersection area.
Mobile communication, multipath propagation mode, signal delays, reflectivity, scatter, trasmissivity, building surface, 62.4 GHz
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