Small-sized low-loss reflector filters utilizing reflection of Bleustein-Gulyaev-Shimizu and shear horizontal waves at free edges of substrate

A Bleustein-Gulyaev-Shimizu (BGS) wave having only shear horizontal (SH) component has the characteristic of complete reflection at the free edges of a substrate with a large dielectric constant. A conventional surface acoustic wave (SAW) resonator filter requires reflectors with many electrode fingers on both sides of interdigital transducers (IDTs). It is considered that small-sized low-loss resonator filters without electrode reflectors can be realized by utilizing this edge reflection in place of the electrode reflectors in the conventional SAW resonator filter. We attempt to realize small-sized low-loss resonator filters by using this characteristic of BGS and SH waves. As a result, in spite of a wirebonded type of packages, resonator filters with very small sizes (3.8×3.8×1.5 mm and 4.5×5.2×1.75 mm) and a low insertion loss in the 52~190 MHz are realized for the spread spectrum (SS) codeless telephone system, the global system for mobile communication (GSM) system, the wide band code division multiple access system (CDMA) (Rx) system, and the narrow band CDMA (Tx) system.