A magnetic-free in-band full-duplex RF front-end with antenna balancing structure

In this article, a design of magnetic-free in-band full-duplex (IBFD) RF front-end with antenna balancing structure is presented. The proposed magnetic-free IBFD RF front-end consists of 3 dB hybrid couplers, a Wilkinson power divider, two transmitter (Tx) antennas, and two receiver (Rx) antennas. The proposed IBFD RF front-end can be implemented and integrated at high frequencies because all the components used in the circuit are non-magnetic devices. Proposed IBFD RF front-end eliminated the 3-dB Tx insertion-loss of the Balun and transformer in conventional IBFD RF front-ends using antenna balancing structure. Moreover, there is no noise figure degradation at Rx because it realized only a passive circuit. The mathematical analysis of the cancellation characteristics between two different signals with magnitude and phase difference variations according to the normalized frequencies is presented. Accordingly, the broadband out-of-phase balancing power splitter and the antenna balancing structure are adopted to achieve broadband SIC. In order to verify the electrical performances of the proposed magnetic-free IBFD RF front-end, it was implemented at the 2.5 GHz WiMax frequency band. When the fabricated IBFD RF front-end was operated with antenna balancing structure, the measurement results show that the 60 dB SIC bandwidth and maximum SIC were 113 MHz (2.446 - 2.559 GHz) and 75.6 dB, respectively.