Theoretical studies of ionospheric radiowave propagation.
2015-11-19T09:18:59Z (GMT) by
This Thesis is concerned with radiowave propagation within and below the Ionosphere at frequencies in the HF and VLF portions of the radio spectrum. The first part of the thesis is devoted primarily to a study of HF propagation based on Ray Theory concepts. An account of Ray Theory is given and the approximations used in the classical treatment are discussed. In particular, the thesis considers the so-called Complex Ray Theory in which the effect of electron collisions on the ray path is introduced. Original results are produced which detail the behaviour of the reflection and coupling points of the propagation modes for both classical and Complex Ray Theory applications. The second part of the thesis is concerned with propagation of VLF waves. The theory is formulated in terms of Waveguide Modes. An account is given of this Theory as it has been applied to the propagation of VLF waves in the Earth- Ionosphere waveguide. Reflection from the Ionosphere is discussed in terms of the classical and generalised Full Wave Theories so that the propagation of these waves may be considered below realistic model ionospheres. A computer programme based on these theories, and which enables the waveguide mode parameters to be calculated, is outlined. Original results are presented on the parametric behaviour of the waveguide modes as a function of frequency and azimuth, using tabulated night time ionospheric profiles. For one of these profiles an interesting feature of the results is the apparent interchange of identity between the two lowest order modes. Further calculations have enabled a comparison of the mode parameters using classical (non-generalised) and generalised Full Wave Theories, and a comparison of the amplitude and phase of measured and theoretically predicted field strengths at distances of less than 1000 Km from a transmitter. Some work on the application of Greens function techniques to discontinuous waveguides is presented.