ERA Technologies of the UK is responsible for carrying out the ESA Telecom funded project. The idea for the project began in 2003 when the company had already developed a Ku band-scanning antenna. It was thought that by coupling a tracking system and receiver equipment to it, a commercially viable device capable of receiving satellite TV services could be constructed for use aboard a variety of vehicles.
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Not only commercial automotive but also High-Speed trains as well as, in the future, aircraft will be the beneficiaries of the antenna. A test bed aboard an SUV (Sport Utility Vehicle) was demonstrated at the recent ASMS conference at ESA ESTEC (image top-left). Another test bed for the American market has also been developed (image right). |
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In order to meet demands laid down by potential customers, the antenna needed to be part of a system which can locate a satellite automatically and track it while the vehicle is moving. For installation in a vehicle, a maximum height profile of 10 cm was required. Equally important were weight and of course, a low cost in order to maximise its market share.
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The completed antenna has a number of innovations, not the least of which is a series of waveguides (image left), each containing a longitudinal slot in one broad wall. A polarizer covers the whole antenna and can be rotated through 90º to receive either clockwise or counter-clockwise polarised TV signals, making the antenna compatible with the US market. |
The signals from each waveguide are combined using a waveguide beamforming structure, It is possible to vary the widths of the radiating waveguides and scan the beam without the use of electronic phase shifters or tilting the antenna.
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Construction of a prototype required ERA to also develop a range of low-cost fabrication techniques for injection moulded plastics. This makes the manufacturing costs comparable to reflectors in high volume applications. Ruggedness was only one of the factors that had to be considered. Height considerations were minimised by carefully optimising the various components. The image at right shows the mechanical layout of the antenna starting with the polarizer, then moving down, the horn, slot and moving plates and finally the motorised base plate. The ERA antenna has a completed height of just 96.5 mm. |
Mass too was a consideration, and all major parts were designed with this mind so that the rotating portion of the antenna has a weight of just 12 kg. The use of plastics in the manufacturing was key to this.
Initial acquisition is generally achieved by detecting a satellite ID code. By having prior knowledge of the satellites that are visible from the operating location, it is possible to achieve very rapid acquisition by identifying the first satellite that is detected, calculating the offset of the wanted satellite, and moving rapidly to this transponder. Once acquired, tracking is maintained by mechanically dithering the antenna and monitoring signal strength.
If the satellite signal is lost, on-board sensors maintain the required look direction while the vehicle is in motion. This allows immediate re-acquisition when the satellite becomes visible again. Rapid re-acquisition can also take place while the on-board sensors remain sufficiently stable. When transmit antennas are included in the system, TX beam pointing is achieved by slaving the TX and RX antennas together.
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Further development of this antenna is currently underway with a prototype for aeronautical applications (image left) expecting its first demonstration in early 2005. |
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"I believe we've built one of the best performing low profile solutions available in the market place," stated Barry Driscoll of ERA Technologies. "It is viable from both technical and commercial standpoints." Partnered with an American company ERA is selling the product in the US market competing direct with local manufacturers. Further applications in Europe are expected. |
To read more about ERA Technologies' Low-cost (and Low-profile) Scanning Array Antenna click under Related Links on the right of this page.
