Abstracts Mathematics

Antenna systems research

by Keith Malcolm Keen

This thesis is an overview of a number of investigations on antenna systems and related subjects over a period of 28 years, which has resulted in 44 publications in the technical literature, one current patent, and an M.Sc. thesis. The investigations have been grouped into 7 categories: - Log periodic antennas, - Antenna performance measurement techniques, - Spacecraft Antenna Systems, - Satcom Terminal Antennas, - Transmission lines and baluns, - High Radar Cross Section Reflectors for Spaceborne Radar Calibration, - Miscellaneous Antenna Investigations. These investigations have resulted in various outcomes: in new antenna types and in improved antenna configurations; in improved techniques for antenna rf performance evaluation; in new knowledge relating to materials used with spacecraft antenna systems; in the development of computer software and computer-numerical methods for specific purposes; and in the advancement of accurate radar cross section prediction methods for spaceborne radar calibration targets. In the discipline of log-periodic antennas, a planar 'printed circuit 1 antenna structure has been devised which has a toroidal shaped radiation pattern distribution with horizontal linear polarization. A non-planar form of this radiating structure with a unidirectional beam has also been demonstrated. Some new techniques for measuring the rf characteristics of antenna systems have been devised. These include special techniques for frequency scaled ship model hf radar antenna measurements, and techniques for measuring scattering from the feed support struts of large Earth station parabolic reflector antennas. A novel method of acquiring near field phase and amplitude data using an interference technique for determining antenna far field performance characteristics by near field to far field data processing transformation has been demonstrated. Correction factors which allow gain comparison measurements to be made in short range length facilities, such as certain types of anechoic chamber, have also been presented. Antenna measurement techniques which are applicable to spacecraft antenna systems have been reviewed. With regard to spacecraft antenna systems, a number of diverse studies have been carried out, one of which has resulted in the composition of a mathematical procedure for predicting the complex beamshapes of contoured beam satellite reflector antenna systems. Also, experimental work has been described which showed that spacecraft reflector antennas constructed with carbon fibre reinforced plastics do not require metallic surface coatings, and that thermal control paint applied to spacecraft does not cause antenna performance degradation. Other programmes of research involved VHP turnstile antenna systems on large satellites, and future technology, geostationary orbit multi-role satellites with 'plug-in' payloads. New satcom terminal antenna configurations has been a very important area of research, resulting in high performance circularly polarized antenna configurations…