Longitudinally coupled resonator filter using edge reflection of Bleustein-Gulyaev-Shimizu and shear horizontal waves with various bandwidths realized by selecting substrates

A conventional surface acoustic wave (SAW) resonator filter requires reflec tors with many grating fingers at both sides of the interdigital transducer s (IDTs). On the other hand. a small-sized low-loss resonator filter withou t grating fingers can be realized by utilizing the reflection of a Bleustei n-Gulyaev-Shimizu (BGS) wave or a shear horizontal (SH) wave at the edge of a substrate. As a result. the authors have developed longitudinally couple d resonator filters using the reflection of BGS and SH waves at the edges o f a substrate. Longitudinally coupled resonator filters on piezoelectric ce ramic substrates for the first intermediate frequency (IF) stage have been realized to be low-loss, small-sized and extremely wide bandwidth (fraction al bandwidth of 15%) filters as compared to the ordinary resonator filters, and they can have various kinds of bandwidths (2 to 15%) by employing cera mic substrates with various electromechanical coupling factors. On the othe r hand, the edge-reflection-type resonator filters on LiTaO3 single crystal for various first IF stages have also been realized to be low-loss and sma ll-sized filters. In spite of being a wire-bonding type of IF filter, the p ackage size of this filter is the same as that of the radio frequency (RF) SAW filter.