Development of small antenna duplexer using SAW filters for handheld phones

For smaller handheld telephones, we have developed a small antenna duplexer. This paper describes the fabrication and characteristics of our duplexer. Our package, which comprises two cavities and impedance control circuits with a strip line, has a multilayered structure. The package is made of glass-ceramic of size 7.5×8.5×2.5 mm³. The conductor patterns of the package are made of Cu. For the SAW filter of the duplexer, we used the ladder type filter composed of one-port SAW resonators. Typical frequency response characteristics of the AMPS specification are 2.5/3.5 dB.(transmitter/receiver) insertion loss at maximum in the 25 MHz passband, and 35/29 dB stopband rejection. We also improved the filter lifetime using a three-layer Al-Cu/Cu/Al-Cu electrode film structure to 300 times the lifetime of a comparable Al-Cu single-layer filter. From the Arrhenius plot, the lifetime was estimated at more than 500000 hours at 120°C for an input power of 1 W