SAW Microstrip Antenna-Duplexer for Radio Communication Transceivers in the GHz Range

Design, fabrication and performance of a SAW microstrip front-end circuit at 1.7 GHz for applications in time division multiple access (TDMA) systems are reported. The front-end consists of a transmitter part (containing a SAW filter for noise suppression and amplifiers), a receiver part (containing a stripline filter for preselection, a SAW filter, and a low noise amplifier), and a duplexing circuit. Both the transmitter SAW filter and the receiver SAW filter are low-loss filters with a center frequency of 1.684 GHz. The substrate material used for the SAW filters is 36rot YX-LiTaO3 and the acoustic wave type is a leaky surface acoustic wave (LSAW). The front-end operates at 1.684 GHz and has a 1 dB-bandwidth of 30 MHz with a pin-diode switch used in the duplexer. The output power at the antenna port is 23 dBm and the transmitter-receiver isolation is better than 50 dB. The present work arose from a requirement of a miniature low-cost front-end for digital cordless telephone systems. The paper also presents some new design and fabrication techniques for low-loss SAW filters in the upper UHF band.