Through an ESA Advanced Research in Telecommunications Systems (ARTES) 5 project called Textile Antennas, Patria has been successful in demonstrating that an antenna can be built using textile or cloth materials that can be worn and used in personal satellite communication.
Explains Rolv Midthassel, TIA-T representative for this project: “Flexible antennas are becoming attractive, since the recent developments in wearable computing have opened several possibilities to integrate wireless functions to clothing.”
Oulu University in Finland is the subcontractor for this project, and have assisted Patria in their efforts. Work performed during this project included complete design flow, from material selection and characterization, to actual design implementation and verification. The resulting demonstrator antenna looks like a simple patch of cloth and is capable to operate at the Iridium and GPS band as part of clothing.
The use of the GPS and the Iridium satellite phone system for this project may be an attractive combination for a later product, says Midthassel. The Iridium satellites allow two-way voice or data communication while the GPS provides positional data to the end-user. Iridium could also be used to send the position of the end user to operational centres.
Three issues were addressed during this project, with the main issue being the selection of the actual material to use. Electrical characterization needed to be made on the material selected and considering this material data is not readily available, a number of measurement techniques needed to be performed.
The second issue was to determine the performance of the antenna when the person wearing it moves around or bends, or if the human body would actually cause a problem with efficiency. Peter de Maagt, ESA technical officer for this project, explains that the particular geometry of the antenna allows it to be bent in a direction that is least harmful for performance. Testing proved that the antenna meets the electrical specifications under bending conditions. The radiating patch antenna is shielded against environmental conditions using a protective layer. The selected geometry meets the stringent requirements imposed by Iridium and GPS, maintaining circular polarization even under bending conditions over the full bandwidth, which is commonly recognized to be hard to achieve with soft, wearable antennas.
The third issue was to find out about the actual manufacturing. Could the material be washed and at how high a temperature? How must it be stitched? Could the material be ironed?
Dr. Pekka Salonen, Research and Development manager for Patria Aviation Oy, says that working with ESA through the ARTES programme has been beneficial. "We have been pushed to go further to show that we can do to reach the goal of what we have promised to do," he says. "Comments and suggestions from ESA staff during the project have been valuable, giving us new insight into all the variables we should take into account, aside from engineering factors. The results we have gained are a good example of successful close cooperation between the customer and contractor."
Testing has indicated that a textile antenna is feasible. One of the tests conducted was to use the antenna to place a call with the Iridium phone to ESTEC, in Noordwijk, The Netherlands, from Patria’s home base in Finland. This test was successful.
“We are pleased with the results of this project,” says Midthassel. “Such an antenna can be used in occupations such as firefighting, or other emergency situations.”
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