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One Antenna Gives Multi-cover
Television viewers would be incensed if, to gain access to the programmes of all available stations, they had to buy individual receivers for each channel.
It is a situation faced worldwide by those needing to communicate with satellites — a single dish antenna provides access to only one individual satellite.
Australia's national science agency. CSIRO. Is about to change that with the launch of Its multi-beam antenna which can track up to 20 satellites at once.
In a recent demonstration in Sydney, the revolution-dry intenna. which was developed with the support of the Australian Department of Defence, simultaneously tuned into two television stations beamed down by Optus satellites. and a third beacon signal from an Intelsat satellite.
■’ CSIRO Division of Radiophysics researcher and team leader Dr Trevor Bird described the multi-beam antenna as completely new.
I "As the world telecommunications market continues lo
expand, it is becoming increasingly impractical for users to have a separate dish for each satellite they need to communicate with," he said.
“What we have here is like having one television set for all five local channels, instead of having to buy a different set for each channel.
Using one multi-beam antenna means you can send and receive signals to and from up to 20 satellites. These signals might include television broadcasts, telephone calls, scientific data or other information."
An example of its value in an everyday situation would be in a block of apartments where many residents might want to watch pay TV, but not all would choose the same programme. The new antenna would provide the variety of selection needed.
Dr Bird said the multi-beam antenna had a' separate feed unit for each satellite. These were able to keep track of their own satellites, so that the main reflector or dish on the satellite did not need to move. All that was needed to gain ac-
cess to another satellite was another feed unit- With conventional systems, the large reflector had to move to track each satellite, limiting each Antenna to only one satellite.
The satellite signal is sam pled as the antenna is rotated on a spherical grid, enabling the antenna's radiation pattern to be obtained. The satellite signal is recorded by another fixed antenna. The resulting data allow application of holographic techniques, including assessing the reflector surface accuracy.
This is repeated for several selected feed locations in the focal region of the antenna. Results obtained show antenna efficiencies have registered better than 65 per cent.
The system is flexible and reliable. Networks can be reconfigured to optimise transponder usage. Stand-by links to an alternative satellite also may be activated if one link fails.
— (Australian Science & Technology Newsletter)