Australia is perhaps the country most suitable in the world for mobile satellite (MSAT) communications. This is because of its size and due to the remote nature of its inland regions. It is therefore not surprising that Australia represents the first country in the world to establish its own full domestic MSAT communications service. Launched in 1994 and called the Optus MobilesatTM service, it was designed to allow mobile users to communicate via satellite from anywhere within the country including 200 km out to sea. Two and a half years before the MobilesatTMservice was launched however, the Australian government in conjunction with a microwave communications firm called Mitec Ltd awarded an Australian Postgraduate Research Award (Industry), APRA(I), to the author of this thesis. The objective of the APRA(I) project was to develop a fully working, low cost vehicle antenna system for use with the future MobilesatTM service of Australia.
When the project was started in January 1992, achieving the main objective was a particularly challenging task for a number of reasons. Firstly, the MobilesatTM service was still in its early development which meant that there were no examples of Australian MSAT antenna systems from which to gain experience. And since Australia was leading the world in the development of its domestic MobilesatTM service, there was little experience to be gained from research overseas. The few antenna designs that had been proposed overseas were generally very costly designs which were being produced to satisfy much different requirements. Consequently, the antenna development performed in the project needed to be pioneering work. In addition, the size of the Australian continent in conjunction with the position of the MobilesatTM satellite(s) made the task very challenging. That is, for a vehicle antenna to be used from the lower regions of the country to the upper regions with the MobilesatTM service, it needs to work over a wide range of elevation angles (approximately 28° to 66°) in order to communicate with the satellite(s). Note that researchers designing systems for other continents such as Europe and Japan, do not face this particular challenge because of smaller elevation coverages required.
Nevertheless despite all of the challenges, the work described in this thesis was completely successful in that the main goal as well as all of the other objectives were fully achieved. To satisfy the main goal, a vehicle mounted antenna array was developed which allows mobile communications via satellite throughout the Australian continent. The vehicle mounted design is a fourteen element electronically steered antenna that achieves more than sufficient gain coverage in the azimuth and elevation directions, without the need for expensive and troublesome phase shifters. The fully operational design uses tilted dual patch array elements and a satellite tracking system to track the satellite as the vehicle moves and changes direction. Testing of the antenna array involved both extensive indoor testing (within an anechoic chamber) and outdoor testing with the design mounted to a land vehicle.
For the project to be successful. a large number of system components needed to be produced in order to form the overall design. These components included antenna array elements , 3 dB quadrature couplers , an array housing, a power division network, and a microprocessor controlled satellite tracking system. In this thesis, the design, development and testing of all of these components is presented. In addition, the thesis describes other investigations which were performed within the project. For example, studies were carried out into the design of increased bandwidth circular and elliptically shaped 3 dB couplers. This was done to produce couplers of increased bandwidth should they be needed for future use with the antenna system. An investigation was also performed into the design of a briefcase system for satellite communications. The motivation behind this work was to produce a low cost alternative design to the vehicle mounted antenna. The briefcase system eventually developed in the project has the advantage that it can be carried by hand and used from areas which are not accessible to land a vehicle. It is also a very user friendly satellite communications system as will be revealed in the pages to follow.