Transversely Coupled Resonator Filters Utilizing Reflection of Bleustein-Gulyaev-Shimizu Wave at Free Edges of Substrate

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Smaller-sized and lower insertion loss surface acoustic wave(SAW)filters are urgently required for mobile telecommunications. We describe here that miniature, low-loss transversely coupled resonator filters without reflector electrodes could be realized and commercialized by utilizing the edge reflection of a Bleustein-Gulyaev-Shimizu(BGS)wave for the first time. The transversely coupled resonator filter has a narrower bandwidth than a longitudinally coupled one. A small, low-loss resonator filter for a first intermediate-frequency stage(first IF)of a spread spectrum(SS)codeless telephone system could be realized using a piezoelectric ceramic substrate with a coupling factor(k)of 0, 20 and the transversely coupled resonator filter consisting of single finger electrodes. A filter for the first IF of the global system for mobile communication(GSM)requires a narrower bandwidth than SS codeless telephone, but a suitable substrate with a small coupling factor is not available. However, we could realize the small transversely coupled filter for GSM using split finger electrodes.
社団法人応用物理学会の論文
2000-05-30