Isolation Bandwidth Enhancement of Electrical Balance Duplexers

In In-Band Full Duplex (IBFD) transceivers, newly suggested Electrical Balance Duplexer (EBD) technique works by coupling transmitter, receiver, antenna, and balancing impedance using a hybrid junction where the balancing impedance needs to be equal to the antenna impedance to achieve a high Transmit-Receive (TX-RX) isolation. This isolation implements a form of self-interference (SI) cancellation to facilitates simultaneous transmission and reception from single antenna. Variations in antenna impedance with respect to frequency significantly reduces the isolation bandwidth and is dominant factor in limiting the isolation. A frequency independent antenna with a core structure of equiangular Archimedean spiral is designed by authors with high impedance stability in ultra-wideband (UWB) frequency domain of 1.5GHz to 3.5GHz while the antenna impedance is smoothened using some electromagnetic techniques. In comparison with the literature, using this antenna in the EBD stage along with a simpler balancing impedance is resulted to six times wider isolation bandwidth in the EBD stage.