Design of a passive self-interference cancellation network with high cancellation ratio

A passive self-interference cancellation network (SICN) is proposed in this paper. The network is composed of three directional couplers and microstrip delay lines. By adjusting the coupling factor of the two parallel coupled line directional couplers and the length of the delay lines, the proposed SICN is able to produce an optimized reference signal with approximate equal amplitude and 180° phase difference to the self-interference signal (SIS), and the cancellation of SIS is thus achieved. Numerical simulation results of the proposed network shows a better reflection coefficient level less than -23 dB over the LTE band of 2.5GHz - 2.57GHz. The cancellation ratio is more than 12dB, while the insertion loss of receive channel is about 0.12dB. Another numerical example for the band of 2.62GHz - 2.69GHz is also simulated and discussed. Details of the proposed cancellation network designs are described and the simulated results are presented and discussed.