The idea lies in the transmitter – actually a series of six subtransmitters – all hooked into an artificial transmission line. Each subtransmitter sends signals at regular intervals, and their individually weighted outputs are programmed so they combine to produce an RF signal in the forward direction at the antenna port, while cancelling out at the receive port.
Because individual outputs are programmable, this allows simultaneous summation and cancellation across a wide range of frequencies and for signal strength to be adjusted at the antenna.
“In one direction, it’s a filter and you basically get this cancellation,” said Professor Alyssa Apsel. “And in the other direction, it’s an amplifier.”
Fellow researcher associate processor Alyosha Molnar, added: “You put the antenna at one end and the amplified signal goes out the antenna; you put the receiver at the other end and that’s where the nulling happens,” Molnar said. “Your receiver sees the antenna through this wire – the transmission line – but it doesn’t see the transmit signal because it’s cancelling itself out at that end.”
The work is said to be build on research reported six years ago by a group from Stanford University, which devised a way for a transmitter to filter its own transmission, allowing weaker incoming signals to be heard.
Unlike the Stanford work, the Cornell group’s subtransmitter concept will work over a range of frequencies.
“This wire is a fairly broadband structure,” Molnar said. “And the thing you do to make it work over a wide range of frequencies is just control those different subgains of the transmitters to make this cancellation always happen.”
Instead of needing a filter for every band, signal separation could be controlled digitally and upgrading to the latest version could be as simple as downloading the latest software.