A UMTS-900 duplexer

Due to its wide bandwidth (35 MHz) and narrow duplex gap (10 MHz), UMTS900 is a very difficult standard for the implementation of the duplexer with current technologies. In this paper, we present the design and performance of a UMTS-900 duplexer based on thin film bulk acoustic resonator (FBAR) technology. We have used external inductors to compensate the inadequate electromechanical coefficient of resonators. Inductors are used to adjust locations of filter transmission zeros to achieve better attenuation in stopband as well. We have achieved very good insertion loss (less than -2 dB) and the Tx/Rx isolation better than -55/50 dB respectively. The size of the duplexer is 3times3 mm.