Two electrical and computer engineering professors at the University of Wisconsin-Madison have received a $1 million grant from the Office of Naval Research to study a new type of antenna for the U.S. Navy’s mobile troposcatter communications systems.
Nader Behdad
McFarland-Bascom Professor Nader Behdad and Duane H. and Dorothy M. Bluemke Professor and Vilas Distinguished Achievement Professor John Booske are leading the project titled “Novel Mobile Troposcatter Communications Antennas Enabled by Rapidly Reconfigurable Phased-Arrays.”
John Booske
In troposcatter communications, radio signals are transmitted toward the troposphere, the lowest layer of Earth’s atmosphere, from which the signals bounce off and scatter. Some of that signal is scattered in the forward direction towards intended receivers, enabling secure over-the-horizon communications without the use of satellites or relay stations.
Troposcatter communications systems were used by the military for several decades until they were mostly replaced by satellite communications. Now, however, as satellite jamming and eavesdropping techniques have become more sophisticated and the demand for high-throughput beyond line-of-sight communications has increased, there is an interest in developing advanced troposcatter technologies to enable secure ship-to-ship and ship-to-shore communications.
The major difficulty is that for these links to work well, they need to have their antennas precisely pointed. On land, fine tuning the large antennas needed to pick up the relatively narrow communications beam can be challenging. But maintaining antenna accuracy and stability on a ship that may be pitching or rolling in rough seas presents another layer of complexity. “Our innovation is really on the antenna side. As the ship is moving, you have to stabilize the antenna beam within half a degree of accuracy towards a given point,” says Behdad.
To do that, the phased array antenna conducts rapid beam scanning which allows it to electronically compensate for the movements of the platform or changes in the environment and maintain the desired direction to send and receive the beam. “These are physically large, fixed structures where you can have lots of teeny-tiny antennas radiating in a synchronous fashion. By basically changing the relative phases of excitation of these different elements you can electronically steer the beam off the antenna,” says Behdad. “If you can do this fast electronic scanning, you can also use the information to figure out exactly where the beam should be pointed to maximize the quality of the connection.”