2X2 MIMO In-band Full Duplex Radio Front-end with 55-dB/60-dB Self-interference Cancellation over 200-MHz/100-MHz Bandwidth

This paper presents a 2X2 MIMO in-band full duplex radio front-end with 55-dB self-interference cancellation (SIC) over 200-MHz bandwidth at 3.7 GHz. For 55-dB SIC, a passive 30-dB suppression is achieved by using an antenna board composed of a decoupling network and circulator with reflection coefficient controller. Additional active 25-dB cancellation is achieved by using a RFSIC board composed of four 3-tap RF cancellers between 2 transmitters and 2 receivers for the broadband operation. Each tap of the RF canceller is composed of a variable attenuator, phase shifter, group delay controller and replaceable delay filter. The RF cancellers can be adapted to not only entire 200-MHz band, but also any channel band between 3.6--3.8 GHz of the antenna board, resulting in a higher SIC. Active 30-dB cancellations and total 60-dB SIC can be achieved when the RF cancellers are adapted to lower and upper 100-MHz bandwidth.