Full-Duplex Communications: Antenna Story

Simultaneous transmit and receive (STAR), also known as in-band full-duplex (IBFD), is a key enabling technology for the next-generation wireless networks operating in spectrum congested and contested environments. Transmitting (Tx) and receiving (Rx) at the same time and over the same frequency channel results in significant improvements in communication systems throughput and spectral efficiency. The chief challenge associated with STAR systems is the required high Tx/Rx isolation that may be obtained with transceivers that combine multiple layers of self-interference (SI) cancellation including digital back-end processing. Since transceivers "start and end" with apertures, the antenna layer is therefore critically important for STAR operation. Nowadays, ~40-50% of the required isolation can be achieved with a well-designed IBFD antenna subsystem inching us ever closer to meeting this, not so long ago considered impossible task. This review focuses on the role of antennas in IBFD systems. Performances of various antennas designed to cover different bandwidths, fields of view, and concepts of use are overviewed. What was deemed impossible a decade ago is now likely.