Ultra-wideband T- and π -type ladder filters using a fundamental shear horizontal mode plate wave in a LiNbO ₃ plate

A fundamental shear horizontal mode (SH 0 ) plate wave in a thin (0°, 115°–120°, 0°) LiNbO 3 plate has electromechanical coupling factor k 2 larger than 50%. In this study, ultra-wideband π -type and T-type ladder filters composed of three SH 0 plate wave resonators were fabricated and characterized. The interdigital transducer (IDT) pitch ( P ) ratio of IDTs in the parallel and series arm resonators (PR: IDT pitch of parallel arm resonator ( P parallel )/that of series arm resonator ( P series )) was experimentally investigated. The 3 dB bandwidth is as large as 33%–61%, depending on the IDT pitch ratio. The insertion loss and shape factor in terms of the IDT pitch ratio are also reported.