Their breakthrough is the design of an antenna that can break reciprocity – the natural symmetry in radiation that characterises antennas. By breaking reciprocity, the researchers’ antenna can control incoming and outgoing signals independently with large efficiency.
“Our achievement is that we break the symmetry between transmission and reception signals, so we are able to prevent the antenna from having to listen to reflections and echoes that affect the source,” said Professor Andrea Alù. “We show that it is possible to efficiently overcome these constraints using temporally modulated travelling wave antennas.”
The advantage of this development is the possibility of sending out a signal, while keeping out noise and echoes that come back toward the antenna. This is likely to enable faster data rates and improved connections, while requiring less bulky antenna systems.
Conventional antennas are subject to reciprocity, meaning they transmit and receive signals with the same efficiency; if a conventional antenna is a very good emitter of signals in a certain direction, it is also a very good receiver from the same direction. This property is not always beneficial, says the team, because transmitting antennas are prone to absorb surrounding reflections or echoes, reducing the quality of the transmitted signals.
In its experiments, the team fed the antenna with two signals simultaneously: the RF signal they wanted to transmit or receive; and a weak low frequency modulation signal that slowly changes the properties of the antenna as the RF signal travels along it. This modulation breaks the antenna’s inherent symmetry in transmission and reception.
The researchers are now looking into how this concept may be extended to applications such as optics, believing that by pushing these concepts to higher frequencies, it will be possible to break a similar constraint affecting energy harvesting devices such as thermophotovoltaic cells.