Practical Millimetre wave Material Characterisation

Abstract

The rapid growth of the RF spectrum for mobile communication creating a challenge to ensure excellent wireless link quality for high data rate. Therefore, the understanding and modelling of the propagation mechanisms in the environment (including reflection and diffraction) are crucial. Propagation mechanism at higher frequency becomes an issue, due to the short wavelength, features of material cause increased scatter, high propagation loss, directivity and sensitivity to blockage. As such, just knowing the composition of the material may be insufficient to understand the propagation mechanism of any signal incident on that surface, and hence the surface roughness itself may become the more dominant feature. This thesis mainly focuses on measurement methodologies, calibration and analysis for materials in the range 20GHz to 60GHz and uses small samples (typically around 40cmx40cm) for the extraction of the pertinent material characteristics. Here two practical methods are considered. Sample materials include metal, concrete, wood and ceramic tiles. The first method uses a transverse measurement technique to identify the diffraction and attenuation of samples. This initial study considered propagation through materials, but it was apparent at an early stage that this is not possible to study material attenuation without an excellent knowledge of the reflection properties of materials. Hence the thesis subsequently concentrates on wideband reflective properties. The transverse measurements helped to yield reflection levels to normal incident signals but do not suitably identify diffuse scatter. The second method considers the angular signal spread with the goal to determine the level of surface reflection and scattering with the different incident signal angle of arrival. Measurements both in an anechoic chamber (5m range at 20GHz) and a shorter range (1m for 60GHz) were performed. Results are able to clearly identify the level of reflectivity and also a good indication of the extent of material scatter. The thesis also includes indoor propagation measurements as a means of determining the more significant effects when considering propagation between transmitter and receiver. This leads to a discussion of what features (material type, size and construction) may be most useful in inclusion in EM propagation modelling. The measurement methodologies and results presented in this thesis provide a useful guideline to extract material properties but also provide insight as to the level of ‘EM details’ required for deterministic propagation models at millimetre wave.

Date of Award	23 Jan 2020
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Andrew R Nix (Supervisor) & Geoff Hilton (Supervisor)