The Refraction of Satellite Signals

Abstract

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.