Low loss and high rejection RF SAW filter using improved design techniques

Abstract

A new high-performance surface acoustic wave (SAW) filter for cordless phone is presented in this paper. The transition characteristics are strongly dependent on a transducer structure and a film thickness owing to the effects of the bulk wave and the electro-mechanical coupling. Similarly the sidelobe characteristics depend on a wire-bonding and an electrode patterning because of the electromagnetic feed through effect. We have simulated and designed with consideration of the bulk wave and the feed through effects using the improved equivalent circuit model. Consequently we have developed a 3 mm square SMD SAW filter with 2.4 dB loss, 5.4 MHz transition bandwidth and over 65 dB sidelobe rejection for 900 MHz ISM band cordless phone systems. The experimental results are in good agreement with the simulations.