Work began in March 1967 with the design and construction of the fixed interferometer (described in Chapter 2) for measuring the elevation angle of arrival of 20MHz signals from the satellite Beacon-B. Also during this first year most of the computing was completed for the theoretical calculations on ray paths presented in Chapter 5; these results along with some previously obtained experimental results form the basis of a paper accepted by Radio Science. Records were obtained from the interferometer from April 1968 to the end of the transmitting life of Beacon-B in January 1970. The analysis of the phase traces from the two aperture interferometer was complicated by the automatic antenna switching procedures; each transit had to be annotated and the useful chart delineated manually before the analysts recorded the phase at intervals of a few seconds on a semi-automatic digital recording system. The antenna switching was designed to save electronics and one channel on the chart recorder, but lead to a computer programming effort which may have been more costly in time and lost transits than the saving achieved by avoiding two separate interferometers (Chapter 2). While this programming and analysis were going on, the computing delays on the University’s overworked IBM 1130 gave time to follow up the idea of recording the fast Faraday fading on 20 MHz signals from a satellite near to or even below the horizon. This project was simplified by the availability of an easily converted 20 MHz receiver and a digital recording system. The report on this project is given in Chapter 4 and also in a short paper. The elevation angle measurements from the interferometer were converted to virtual height increment versus equivalent vertical frequency plots and thence to electron density profiles (Chapter 3, Part I). This analysis was developed from ideas given originally by Titheridge (1964). The interpretation of the resulting values of the scale height at the peak (Chapter 3, Part II) in terms of ionosphere morphology depended heavily on the total content hourly values maintained on computer disk by Dr Titheridge. The results and discussion in Chapter 3 will be presented as a separated paper. Chapter 6 is a review of the effects of the ionosphere on transmitted satellite signals and in particular gives a wider view of Faraday fading than is normally taken. Because of its general nature Chapter 6 can serve as an introduction to satellite radio propagation techniques; it appears at the end of this thesis as common ground after the diversions of Chapters 4 and 5. Since this work falls into three separate projects of ray elevation angle measurements, fast Faraday fading, and second order Faraday rotation calculations, the reports on each have been written with minimal cross referencing; this should facilitate reading but has resulted in a small amount of repetition.

The single-polynomial method for ionogram analysis is adapted to give a least-squares procedure in which the number of scaled virtual heights is greater than the number of terms in the real-height polynomial. The general principles are described in detail and the procedure is applied to the valley problem in bottomside ionogram analysis. It is shown that only a single parameter, the integrated valley ionisation, is obtainable from typical ionograms. The least-squares technique is then applied to the problem of topside ionogram analysis where the facility for using any mixture of ordinary and extraordinary ray virtual depth data is very useful. The method is shown to offer many advantages over the more traditional methods. The effects of horizontal ionisation gradients on bottomside and topside ionograms are extensively investigated by a new technique for synthesising ionograms corresponding to a given model of a moving disturbance in the ionosphere. A number of interesting and important ionogram characteristics are identified and explained. Finally, the specific problem of a large disturbance seen on total electron content records during summer nights is briefly re-examined using topside ionogram data. It is suggested that the disturbance is not primarily a topside phenomenon as originally supposed.

Chapter 1 Introduction. The magnetic field lines that emerge from the polar regions extend to great distances from the earth. The auroral zone closely approximate the boundary between those field lines that are closed within the magnetosphere and those that form the geomagnetic tail. the field lines int he tail may be open or possibly joined with the interplanetary field. this introduces considerable coupling between the polar ionosphere and the distant regions of the earth's atmosphere. High energy charged particles from the sun and disturbances in the magnetosphere, therefore cause large changes in the polar ionosphere, with auroral displays and regions of increased or irregular ionisation. Increasing attention is therefore, being paid to studies of the polar ionosphere to gain some insight into the changes occurring at great heights.

Work began in March 1967 with the design and construction of the fixed interferometer (described in Chapter 2) for measuring the elevation angle of arrival of 20MHz signals from the satellite Beacon-B. Also during this first year most of the computing was completed for the theoretical calculations on ray paths presented in Chapter 5; these results along with some previously obtained experimental results form the basis of a paper accepted by Radio Science. Records were obtained from the interferometer from April 1968 to the end of the transmitting life of Beacon-B in January 1970. The analysis of the phase traces from the two aperture interferometer was complicated by the automatic antenna switching procedures; each transit had to be annotated and the useful chart delineated manually before the analysts recorded the phase at intervals of a few seconds on a semi-automatic digital recording system. The antenna switching was designed to save electronics and one channel on the chart recorder, but lead to a computer programming effort which may have been more costly in time and lost transits than the saving achieved by avoiding two separate interferometers (Chapter 2). While this programming and analysis were going on, the computing delays on the University’s overworked IBM 1130 gave time to follow up the idea of recording the fast Faraday fading on 20 MHz signals from a satellite near to or even below the horizon. This project was simplified by the availability of an easily converted 20 MHz receiver and a digital recording system. The report on this project is given in Chapter 4 and also in a short paper. The elevation angle measurements from the interferometer were converted to virtual height increment versus equivalent vertical frequency plots and thence to electron density profiles (Chapter 3, Part I). This analysis was developed from ideas given originally by Titheridge (1964). The interpretation of the resulting values of the scale height at the peak (Chapter 3, Part II) in terms of ionosphere morphology depended heavily on the total content hourly values maintained on computer disk by Dr Titheridge. The results and discussion in Chapter 3 will be presented as a separated paper. Chapter 6 is a review of the effects of the ionosphere on transmitted satellite signals and in particular gives a wider view of Faraday fading than is normally taken. Because of its general nature Chapter 6 can serve as an introduction to satellite radio propagation techniques; it appears at the end of this thesis as common ground after the diversions of Chapters 4 and 5. Since this work falls into three separate projects of ray elevation angle measurements, fast Faraday fading, and second order Faraday rotation calculations, the reports on each have been written with minimal cross referencing; this should facilitate reading but has resulted in a small amount of repetition.

The single-polynomial method for ionogram analysis is adapted to give a least-squares procedure in which the number of scaled virtual heights is greater than the number of terms in the real-height polynomial. The general principles are described in detail and the procedure is applied to the valley problem in bottomside ionogram analysis. It is shown that only a single parameter, the integrated valley ionisation, is obtainable from typical ionograms. The least-squares technique is then applied to the problem of topside ionogram analysis where the facility for using any mixture of ordinary and extraordinary ray virtual depth data is very useful. The method is shown to offer many advantages over the more traditional methods. The effects of horizontal ionisation gradients on bottomside and topside ionograms are extensively investigated by a new technique for synthesising ionograms corresponding to a given model of a moving disturbance in the ionosphere. A number of interesting and important ionogram characteristics are identified and explained. Finally, the specific problem of a large disturbance seen on total electron content records during summer nights is briefly re-examined using topside ionogram data. It is suggested that the disturbance is not primarily a topside phenomenon as originally supposed.

Chapter 1 Introduction. The magnetic field lines that emerge from the polar regions extend to great distances from the earth. The auroral zone closely approximate the boundary between those field lines that are closed within the magnetosphere and those that form the geomagnetic tail. the field lines int he tail may be open or possibly joined with the interplanetary field. this introduces considerable coupling between the polar ionosphere and the distant regions of the earth's atmosphere. High energy charged particles from the sun and disturbances in the magnetosphere, therefore cause large changes in the polar ionosphere, with auroral displays and regions of increased or irregular ionisation. Increasing attention is therefore, being paid to studies of the polar ionosphere to gain some insight into the changes occurring at great heights.

Work began in March 1967 with the design and construction of the fixed interferometer (described in Chapter 2) for measuring the elevation angle of arrival of 20MHz signals from the satellite Beacon-B. Also during this first year most of the computing was completed for the theoretical calculations on ray paths presented in Chapter 5; these results along with some previously obtained experimental results form the basis of a paper accepted by Radio Science. Records were obtained from the interferometer from April 1968 to the end of the transmitting life of Beacon-B in January 1970. The analysis of the phase traces from the two aperture interferometer was complicated by the automatic antenna switching procedures; each transit had to be annotated and the useful chart delineated manually before the analysts recorded the phase at intervals of a few seconds on a semi-automatic digital recording system. The antenna switching was designed to save electronics and one channel on the chart recorder, but lead to a computer programming effort which may have been more costly in time and lost transits than the saving achieved by avoiding two separate interferometers (Chapter 2). While this programming and analysis were going on, the computing delays on the University’s overworked IBM 1130 gave time to follow up the idea of recording the fast Faraday fading on 20 MHz signals from a satellite near to or even below the horizon. This project was simplified by the availability of an easily converted 20 MHz receiver and a digital recording system. The report on this project is given in Chapter 4 and also in a short paper. The elevation angle measurements from the interferometer were converted to virtual height increment versus equivalent vertical frequency plots and thence to electron density profiles (Chapter 3, Part I). This analysis was developed from ideas given originally by Titheridge (1964). The interpretation of the resulting values of the scale height at the peak (Chapter 3, Part II) in terms of ionosphere morphology depended heavily on the total content hourly values maintained on computer disk by Dr Titheridge. The results and discussion in Chapter 3 will be presented as a separated paper. Chapter 6 is a review of the effects of the ionosphere on transmitted satellite signals and in particular gives a wider view of Faraday fading than is normally taken. Because of its general nature Chapter 6 can serve as an introduction to satellite radio propagation techniques; it appears at the end of this thesis as common ground after the diversions of Chapters 4 and 5. Since this work falls into three separate projects of ray elevation angle measurements, fast Faraday fading, and second order Faraday rotation calculations, the reports on each have been written with minimal cross referencing; this should facilitate reading but has resulted in a small amount of repetition.

The single-polynomial method for ionogram analysis is adapted to give a least-squares procedure in which the number of scaled virtual heights is greater than the number of terms in the real-height polynomial. The general principles are described in detail and the procedure is applied to the valley problem in bottomside ionogram analysis. It is shown that only a single parameter, the integrated valley ionisation, is obtainable from typical ionograms. The least-squares technique is then applied to the problem of topside ionogram analysis where the facility for using any mixture of ordinary and extraordinary ray virtual depth data is very useful. The method is shown to offer many advantages over the more traditional methods. The effects of horizontal ionisation gradients on bottomside and topside ionograms are extensively investigated by a new technique for synthesising ionograms corresponding to a given model of a moving disturbance in the ionosphere. A number of interesting and important ionogram characteristics are identified and explained. Finally, the specific problem of a large disturbance seen on total electron content records during summer nights is briefly re-examined using topside ionogram data. It is suggested that the disturbance is not primarily a topside phenomenon as originally supposed.

With the increase in and more diverse applications of microwave radio communications, the probability of a signal propagating through a medium of vegetation is increased. As a direct result of this demand for microwave communication systems, knowledge is required of the effects of vegetation media on the propagating microwave signal. This enables radio system planners to predict the signal loss more accurately, necessitating a detailed study of the propagation effects of vegetation. A vegetation depth attenuation model has been developed based on the International Telecommunications Union-Radio Sector model and validated against measurements conducted at two microwave frequencies of 11.2 GHz and 20 GHz. The measurements were conducted on a number of sites of differing geometries at different times of the year to obtain the two extreme states of foliage, in- and out-of-leaf. The trees found at the sites were of a number of indigenous species. A variety of species and environments were employed for the outdoor measurements as it was felt that any variation in the signal, occurring as a direct result of the species, climate, environment etc., would be reduced. A further study has been conducted in an anechoic chamber, the purpose being to investigate the depolarising effect of vegetation, to characterise and to ascertain how and to what extent the polarisation of the incident signal is changed as it passes through the vegetation without the effects of climate, location and environment affecting the resultant signal. To enable larger quantities of data to be obtained, collated and subsequently analysed and also to remove any scope for error during the collection of results, two data acquisition programs were written for the two main environments in which the measurements were to be undertaken, that is to say, outdoor and indoor (anechoic chamber) environments. In seeking to provide a model for the prediction of attenuation a radio wave will suffer as it is propagated through a body of vegetation, several models have been examined in turn and their relative merits discussed together with their applicability to the study. After examining the possible models available, the thesis provides a model which enables the prediction of additional attenuation a radiowave signal will suffer as a function of path length (depth) of the vegetation medium and frequency. The model can be recommended for use in the 10-30 GHz band. The study on the depolarisation of signals by vegetation has shown that the components of a vegetation medium e.g. tree trunks, branches and leaves, can cause considerable changes in the polarisation of the incident signal as it propagates through a volume of vegetation. The work presented in this thesis contains new measured results of the polarisation state of the radio wave as it emerges from a vegetation specimen. These results obtained in an anechoic chamber under controlled conditions have demonstrated that additional effects, other than attenuation by absorption and scatter need to be considered in order to characterise and subsequently model the overall effect of vegetation in the radio path of propagating signals.

In Code Division Multiple Access (CDMA) systems forward error correction (FEC) is an important factor in improving system performance. Because of the multiple access interference observed in asynchronous CDMA, FEC is required to improve system capacity. Several alternative coding techniques are available, including "trellis codes" specifically designed for CDMA, very low rate convolutional codes and conventional convolutional codes. An analytic approach is developed to compare the performance of different coding techniques for CDMA on the same basis by extending several improved analysis techniques which were developed for uncoded CDMA. Analytic results are presented for additive white Gaussian noise (AWGN) channels and frequency non-selective Rician Fading (FNRF) channels. The performance of coded CDMA systems in frequency selective Rayleigh fading channels is also analyzed using simulation techniques. Both analytic and simulation results show that by using trellis codes or very low rate convolutional codes significant performance improvement is achieved over conventional convolutional codes. Trellis codes outperform very low rate convolutional codes in AWGN and FNRF channels while both codes show similar performance in frequency selective Rayleigh fading channels. / Master of Science