A new radio telescope composed of an array of antennas is under development at the National Research Council. Each antenna includes a large scale multi-tethered aerostat system to hold the telescope receiver at the reflector focus. This receiver is located at the confluence point of the tethers. Starting from a previously developed dynamics simulation of the triple-tethered aerostat system, an existing statics model of the same system is incorporated into the simulation to provide an initial equilibrium condition for the dynamics. A spherical aerostat is used in both models. The two models show a very good match with each other after being merged together. This combined computer model is further developed to study the use of six tethers and the use of a streamlined aerostat instead of a spherical one. In the case of the six-tethered system, two topics were investigated: using the six tethers to control the position of the airborne receiver only; and using the six tethers to control the orientation of the receiver as well as its position. A streamlined aerostat is also modelled by a component breakdown method and incorporated into the triple-tethered system to replace the spherical one. The main findings from the simulation results are as follows: (1) the six-tethered system with reductions in the tether base radius and the tether diameter exhibited increased stiffness compared to the triple-tethered system when used to control the receiver position only; (2) the six-tethered system showed difficulty achieving satisfactory control for both the position and orientation of the receiver; (3) the streamlined aerostat showed no oscillations typical of a spherical one but the system requires more power to control in the presence of wind turbulence.

Thesis (Ph. D.)--University of Sydney, 2008. / Includes graphs and tables. Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Physics, Faculty of Science. Bibliography: p. 196-203. Also available in print form.

The Hartebeesthoek Radio Telescope is well suited to mapping large areas of sky at 2.3 GHz because of the stability and sensitivity of the noise-adding radiometer (Nicolson, 1970) and cryogenic amplifier used at this frequency, the relatively large 20' beam of the 26 m dish antenna, and its high-speed drive capability. Telescope control programs were written for the Observatory's online computer for automated mapping. Effort centred on removing the curved baseline or 'background' from each Declination (Dec) scan, due to atmospheric and ground radiation contributions varying as the antenna is scanned. Initially these backgrounds were measured over a wide range of Hour Angle (HA) for the Dec range of a map, and an interpolated curve subtracted from each on-source scan for its HA. A common base level was established by comparison with drift scans (observed with the antenna stationary). These different observations (on- and off-source Dec scans and drift scans) were combined into one in the Skymap system by performing Dec scans at a fixed starting HA for a period long enough to permit 'cold sky' and the source to drift through. A background formed by fitting a smooth curve through the lowest sample at each Dec provides a consistent relative base level for all the scans in an observation. A high scanning speed is used so that observations may fruitfully be repeated three times and interleaved to build a reliable, fully sampled map. As each observation has its own background removed, it may be made at any HA. For comparison, maps of Upper Scorpio produced by the earlier method (Baart et al., 1980) and the Magellanic Cloud region produced by Skymap (Mountfort et al., 1987) are shown. Skymap provides a simple and flexible mapping method which relies on the stability of the noise-adding radiometer and high-speed repeated scans to produce good maps of large or small extent with little computation. Correction for drift is more difficult than with systems which use intersecting scans, such as the 'nodding' scans used by Haslam et al. (1981) or the Azimuth scans of Reich (1982).

The performance of the Rhodes 22 GHz radio telescope and its improvement are discussed in this thesis. The reflector surfaces of the Cassegrain antenna were surveyed and the surface errors minimised, while the magnitude of thermal and gravitational defomations was calculated. The design and operation of the microwave front end has been improved, and the mixer performance characterised. The continuum and spectral line receivers and their sensitivity are described. The aperture efficiency, which has been raised from 0,47 to 0,57, was deduced from solar and lunar observations and atmospheric attenuation measurements. The antenna beam pattern was also obtained from the observations, with the aid of a computer program, and is compared to that predicted for the telescope.

This is an investigation of the proposed ‘Square Kilometer Array’ (SKA) for the next generation radio telescope. A parallel plate system with a circular reflector has been investigated for SKA to achieve wideband performance and beam scanning ability, in particular the theoretical analysis of the fields in the parallel plate structure using a combination of Finite Difference Time Domain method and Physical Optics. This study builds on earlier work, explores the possible limits of extension and develops an analysis of the device, which will allow all possible configurations to be simulated. It is anticipated that the final scanning arrangement will consist of at least a double reflector system, possibly with some re-configurability, where the parallel plates will have two 180 degree bends with the output being some form of directly radiating aperture. Results were obtained for a Re-configurable Monopole, where diodes are used as switches to physically vary the length of the antenna element and hence increase the bandwidth of the antenna. Re-configurable reflectors were also investigated and Geometrical Optics was used for shaping a dual-reflector Cassegrain system for beam scanning. All of these methods have produced satisfactory practical and analytical results / Doctor of Philosophy (PhD) Electrical Engineering

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