A major challenge in telecommunications is placing antennas in a highly dense environment. Since typical non-magnetic radiators or scatterers obey reciprocity and have time symmetric responses, radiation patterns of an antenna in transmit and receive modes are identical. Because of this, densely placed antennas are prone to receiving echoes of their own transmission, mutual influence from other antennas, or noise. Breaking this temporal symmetry can realize antennas that can transmit without receiving, but this typically requires bulky and expensive rare-earth metals.
Researchers at The University of Texas at Austin have developed technologies for eliminating reciprocity constraints in radiating and scattering systems such as antennas, metasurfaces, or frequency selective surfaces. The researchers use a relatively simple, compact, and inexpensive scheme of space-time modulation of a given structure. The technology works by changing the electric material properties of the structure simultaneously in space and time. The resulting design exhibits a non-reciprocal transmission response—namely, a signal that propagates and impinges on the surface at a given direction will be fully transmitted, while a signal propagating from the complementary direction will be fully reflected. In contrast with current methods of breaking radiating and scattering reciprocity which require bulky and expensive rare-earth metals, this method is cost-effective and simple. It can be implemented with off-the-shelf electronic components which may also allow for real-time reconfigurability, not easily achieved or even possible before.
This invention offers a simple and low-cost technique to break the radiating and scattering temporal symmetry which can limit the performance of communication systems. It has been demonstrated experimentally by loading traveling-wave antennas with varactor diodes which are modulated in space and time. This antenna configuration was shown to transmit with high directivity in a certain direction and not receive from that direction, and vice versa. It has also been conceived in a communication system with multiple antennas in close proximity operating in similar or different frequency bands. The technology serves to reduce the antennas’ mutual influence without limiting their performance.
Left: equal absorption and emission due to reciprocity constraint limits the performance of communication systems. Right: non-reciprocity may be used to improve performance