High performance low-loss SAW filters for mobile radio with improved stopband rejection

A low-loss surface acoustic wave (SAWs) filter configuration is presented that uses a dual-track configuration with a transducer coupling between the tracks. This filter was developed to obtain a high stopband rejection, small passband ripple, and small size, which is needed in mobile communication systems. A partial finger-splitting and an optimized binary withdrawal weighting were also incorporated into the design together with a nonresonant unidirectional configuration. Filters at 450 MHz were fabricated on 36°rotYX-LiTaO₃ using a simple single-layer technology. An insertion loss of 3 to 4 dB was achieved over a bandwidth of 6.5 MHz with a passband ripple of less than ±0.5 dB. The stopband rejection is better than 50 dB