Passive and Active Electrical Balance Duplexers

Electrical balance duplexing enables simultaneous transmit and receive from a single antenna; however, the transmit-to-receive isolation depends on the ability of the balancing algorithm to determine the correct balancing impedance. A novel balancing algorithm based on in situ characterization of the duplexer self-interference channel is proposed. The algorithm requires no a priori knowledge of the antenna impedance or hybrid junction characteristics and automatically compensates for circuit imperfections. A novel balancing network implementation that uses active signal injection is also proposed. A hardware prototype implementing the proposed balancing algorithm and combining passive and active balancing techniques has achieved 81.5-dB isolation over an 80-MHz bandwidth.