Ultra-wideband T- and π-type ladder filters using a fundamental shear horizontal mode plate wave in a LiNbO3 plate

A fundamental shear horizontal mode (SH0) plate wave in a thin (0 degrees, 115 degrees-120 degrees, 0 degrees) LiNbO3 plate has electromechanical coupling factor k(2) larger than 50%. In this study, ultra-wideband pi-type and T-type ladder filters composed of three SH0 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. (C) 2019 The Japan Society of Applied Physics