Abstract: 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. It incorporates varactors, instead of fixed or mechanically adjustable capacitors, 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. It can be implemented as a Monolithic Microwave Integrated Circuit (MMIC).