Wideband RF Self-Interference Cancellation Circuit for Phased Array Simultaneous Transmit and Receive Systems

Abstract

With the growing demand for spectrum utilization, the concept of full duplex transceivers has become attractive. These simultaneous transmit and receive systems (STAR) are attractive as they double bandwidth utilization. To realize STAR, we must suppress self-interference (SI) between transmit and receive antennas. Doing this across a wide bandwidth presents an even greater challenge. Further, for antenna arrays, SI can be higher due to mutual coupling among neighboring elements. In this paper, we achieve 100 dB isolation for practical STAR, across a large 500 MHz bandwidth. Specifically, four stages of the self-interference cancellation are proposed. In addition to high isolation cross-polarized array elements, we employ multi-tap filters at the transceiver RF front-end for interference cancellation. These filters emulate direct SI coupling using frequency-domain optimization techniques. Measured results show an average of 25 dB filter cancellation is possible across 500 MHz.