Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Inaug.-diss.--Königsberg i. Pr.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: Theodore S. Rappaport. Vita. Includes bibliographical references.

No description available.

No description available.

The growing usage and demand for microwave communications has led to the increase in system density, particularly in urban areas, and consequently to the increase in the probability of mutual interference between systems sharing the same frequency band. Satellite and point to point microwave communication systems might have to rely on site shielding to reduce the level of this co-channel interference. In urban areas, there is a great possibility of a building obstructing the interference path, thus providing protection. However, there could be more than one interference path. Scattered interference from other buildings in the vicinity of the site is one which can be found to be almost as harmful as the direct interference. Although site shielding has long been identified as an interference reduction technique, most studies have been devoted to the protection obtained from the obstruction of interference paths, namely diffraction. There is little information available regarding the effects of building scatter in site shielding. The work reported in this thesis was set to carry out theoretical and experimental investigations and characterisation of building scatter. The studies are aimed at the effects of building scatter on site shielding at microwave frequencies. Building scatter prediction models are developed based on Fresnel-Kirchhoff diffraction theory and verified against results obtained from measurement campaigns conducted at a frequency of 11.2 GHz using firstly a perfectly conducting reflector and later a number of buildings in urban environments as the scattering obstacles. Scattering prediction models are developed as extending to that originally applicable to the far field for use in the near and very near field regions of the scattering surface. The very near field model is found to be particularly useful in site shielding applications in urban environments. Furthermore, it has been possible to establish the scattering characteristics in terms of angular and distance dependence of the scattering coefficient using the expansions of the Fresnel integral with appropriate approximations. The effects of building features and surface variations, e.g. protruding and recessed features, windows and surface deviations, are analysed and characterised. These effects are particularly significant in the interpretation of measurement results obtained from buildings in typical urban environments. The thesis provides a prediction procedure which radio system planners and design engineers can use for determining the effects of building scatter on the site shielding factor for specified radio path geometries. The procedure is expected, through UK study group 3, to add considerably to a revised ITU-R (CCIR) procedure and recommendations for building scatter effects in radiowave propagation. The work has also contributed regularly to the technical output of European COST project 235.

Wireless Communications are revolutionising personal and telecommunications services and the way in which they are utilised. Overall growth in cellular, fixed and satellite communication system markets in recent years has exceeded expectations. There is a widespread anticipation that customer demand for wireless telecommunication systems will continue to expand in the foreseeable future. Such systems rely in their planning, design and implementation on the availability of radiowave propagation models. These models are required to describe and characterise with sufficient accuracy the interaction of radiowaves with the environment, especially the various obstacles in the radio path. Prediction tools are highly desirable to radio planners in achieving appropriate coverage planning, determination of the propagation modes and the prediction and control of mutual co-channel interference between existing and new radio links. In the case of land mobile systems as well as wireless fixed access systems, trees, singly or in a group, are usually present in the radio cell environment, giving rise to both absorption and scatter of radio signals. An important part of the modelling process applied to vegetation effects is aimed at analysing the radio propagation modes and the identification of individual signal contributions to the scattered signal caused by various elements of the tree. Past research work on vegetation available in the literature does not account for the interaction between an incident plane wave and individual elements constituting the tree. The work reported in this thesis describes detailed studies aimed at the characterisation of propagation mechanisms arising in single trees of various types. It explores effects of geometrical and physical properties of the tree on radiowave propagation modes arising specifically, i.e. absorption, scatter and depolarisation. These have been addressed through a combination of analytical, computational and experimental modelling, based on thorough examination of the re-radiation functions of single trees. Appropriate measurements performed in both anechoic and outdoor environments at microwave and millimetre wave frequencies, covering frequency band from 2 to 62.4 GHz, provided both model validation and a deeper insight into the problem. Single tree scatter has been shown to be modelled adequately in terms of a re-radiation function with parameters which can be deduced from measured data. This is an important extension to the Radiative Energy Transfer (RET) model, which hitherto has been applied to a homogeneous forest half space. Forward, side and back scatter regions have been identified and characterised. Depolarisation effects were subjected to detailed study with the help of an idealised metallic structure. Analyses of measured results provided deep insight into the causes of depolarisation and the specific polarisation states likely to arise in vegetation. Reasons for signal fades or nulls in the re-radiated signals are established. Wideband channel measurements performed at 2 GHz provided valuable information on the dispersive effects of single trees, whose subsequent analyses revealed the sources of scattering, effects of tree elements, e.g. leaves and branches, and wind effects. The thesis provides also a novel method based on the Finite Difference Time Domain (FDTD) technique, used in studying the propagation modes due to interaction with single trees, starting from primary models for leaves, trunk and branches. Re-radiation fields in 3D of the entire tree are predicted by combining the effects of the single elements forming the tree. The model is shown to be capable of predicting the near-field radiated signal and the radar cross section (RCS). RCS predictions yielded good agreement with measurements and have provided a good basis for a planning model capable of accounting for single trees in the radio path. Overall, the thesis contributes new information, results and models which are very useful in radio system planning and design of broadband wireless communication services.

The overall growth in cellular, fixed and satellite communications markets, has exceeded many expectations and there is a widespread anticipation that the demand for wireless telecommunication systems will continue to expand in the foreseeable future. Such systems rely in their planning, design and implementation on the availability of radiowave propagation models. In the particular case of land mobile radio systems and wireless fixed access systems, obstacles in the form of vegetation volumes, e.g formations of trees, are likely to influence radio propagation, giving rise to absorption and scattering of radio signals. In this context, this thesis investigates suitable techniques to characterise and model the effects of inhomogeneous volumes of vegetation on the propagation modes of radiowaves. The thesis proposes an enhanced model based on the Radiative Energy Transfer theory (RET) which was discretised to accommodate forests formed by different vegetation species with their distinct propagation characteristics. The discretised model computational structure, comprises several element cells, whose characteristic propagation parameters may be assigned independently. The discretised RET (dRET), is therefore capable of gathering the interactive responses between the element cells comprising the computational structure, leading to the determination of the received signal inside or around a given illuminated vegetation medium. The performance of the proposed model, was assessed utilising results from an extended range of measurements, carried out in different environments. Such measurements comprised those necessary for the model input parameters extraction. Others enabled the model assessment through comparison between the model predictions and the actual directional profile of the measured received signal results. An initial assessment of the model was carried out in the laboratory, using an idealised test forest formation placed inside an anechoic chamber, whereas the final model assessment was performed in an outdoor tree groupings formed by several different full size trees. Both indoor and outdoor measurements, confirmed good overall model performance and predictions of both absorption and scattering propagation modes caused by the presence of vegetation in the radio path. This was demonstrated at micro- and millimetre wave frequency bands, centered at 11.2, 20, 40 and 62.4 GHz frequencies. The thesis provides a valid tested method to evaluate the dRET propagation parameters for various isolated volumes of vegetation. Such parameters, may subsequently be utilized into the proposed propagation model, which is shown to be capable of dealing with typical and non homogeneous forests thereby effectively predicting the received signal directional profile at several locations inside and around the inhomogeneous forest. The thesis has many novel features. These include the development and extension of the basic dRET model removing many limitations. The parameter extraction including the effects of the receive antenna radiation pattern is another novel contribution. Further novelty lies in the application of the dRET model to mixed, finite and inhomogeneous vegetation formations. As a result of these refinements and extensions, the dRET propagation model has been shown to yield predicted results which agree well with measurements.

The ever growing application of wireless communication systems requires accurate models for characterising radiowave propagation when affected by the presence of a variety of obstacles. In particular if the obstacles take the shape of vegetation volumes, like single trees or groups of trees and are present in the radio path, they give rise to absorption and scattering of radio signals. This thesis presents a literature review of common models for radiowave propagation through vegetation, the theory of Radiative Energy Transfer (RET) is one of these models and provides an accurate analysis of radiowave propagation through a vegetation media. Extensive measurements have been designed and conducted in a controlled indoor environment to provide valuable measurement data for later development of deconvolution approaches. It can be shown that the measured directional spectra are convolution products of the phase function pattern and the receiver antenna radiation patterns, which impacts determination of the RET input parameters. Consequently, in order to achieve more accurate determination of the RET input parameters, the adverse influence caused by receiver antenna radiation patterns have to be removed from measured directional spectra by implementing a process of deconvolution. This thesis provides successful implementation of two iterative based deconvolution techniques on the measurement directional spectra. To the author's knowledge, this is its first kind of application to eliminate distortion caused by the receiver antenna radiation pattern during measurements. This thesis reports a number of novel approaches. These include the further development and extension of deconvolution techniques such as combining the Bennia-Riad criterion and an error function to determine optimal parameters, as well as using pre-filtering techniques to improve the deconvolution results. Development of clearly defined criteria based on the knowledge of the central-limit theorem and discussion of loss of information avoidance during convolution is another novel contribution. Further novelty lies in the modification of the two methods to suit implementation on the measurement data from radiowaves impacting on vegetation volumes. As a result of these refinements, extracted RET input parameters from the restored patterns after applying the deconvolution processes show evident improvements compared to those extracted from directly measured patterns. Early stage results of this project are published in the IEEE Proceedings on Next Generation Applications, Services and Technologies.