Differential Arrays for Butler Multi-Beam STAR

Simultaneous transmit and receive (STAR) over the same frequency range enables in-band full duplex (IBFD) communication with doubled spectral efficiency. This paper presents an IBFD system that connects an antenna array with a multi-beam former to decrease the impact of the self-interference (SI) existing between the transmitter (Tx) and receiver (Rx) in a multiple input and multiple output (MIMO) system. Physical symmetry is used to cancel near-field coupling. Reflections of the Tx from the surrounding environment usually leak into the receive antennas to cause SI with long delay-bandwidth products that are notoriously hard to remove; the proposed differential array greatly reduces such interference.