This invention provides a novel electronically tunable active duplexer for wireless transceiver applications. It relates to an active duplexer with full-duplex operation, permitting simultaneous transmission and reception of signals at same or different frequencies. Instead of incorporating fixed or mechanically adjustable capacitors, and even instead of incorporating varactor diodes, it incorporates one or more capacitance tuning circuit in phase shifting networks enabling one to electronically tune, with ease and precision, the frequency at which isolation is desired, over a band in both transmit and receive modes of operations.