Design and performance of SAW microstrip antenna-duplexers for mobile phones in the UHF-band

Low-cost hybrid-integrated surface acoustic wave (SAW) filter duplexers consisting of receiver top filter, transmitter final-stage filter and antenna terminal have been developed. The prototype designs were oriented at the GSM system specifications in the 900 MHz-band. Three-stage ladder-type SAW filters having 3dB-bandwidths of 44 MHz at their center frequencies of respectively 902.5 MHz and 947.5 MHz and an insertion loss of 1 dB have been designed to perform the duplexing function by the use of only one transmission line. Leaky SAW phenomena as well as parasitics of package and chip layout effects have thoroughly been taken into account, and a very good agreement between simulation and measurement has been obtained. In the transmitter (Tx) and receiver (Rx) path, the complete duplexer has respectively an insertion loss of 1.2 dB (Tx) and 2.1 dB (Rx) and a 3 dB-bandwidth of respectively 40.1 MHz (Tx) and 47.4 MHz (Rx).