Wide-band duplexer based on electrical balance of hybrid transformer having two notches

A tunable transformer duplexer having two notches has been proposed and demonstrated for a broadband operation. The suggested duplexer using GaAs pseudomorphic high electron mobility transistor (pHEMT) technology shows isolations of over 55 dB at the transmitter (Tx) band and over 45 dB at the receiver (Rx) band across 145 MHz bandwidth. The insertion losses are -3.35 and -3.52 dB for the Tx band and the Rx band, respectively, for 500 MHz bandwidth. At all ports, the return losses are under -15 dB. The duplexer is tunable simply by tuning the four components. Although this broadband duplexer has a very compact size with tunable capability, its performance is comparable with the front end module integrated duplexer.