title: Operation mechanism of double-mode surface acoustic wave filters with pitch-modulated IDTs and reflectors.
abstract: One of the authors (KH) previously proposed pitch-modulated interdigital transducers (IDTs) and reflectors for developing low-loss and wideband longitudinally coupled double-mode SAW (DMS) filters. This paper discusses how a wide and flat passband is realized by applying the pitch-modulated IDTs and reflectors to DMS filters. It is shown that the pitch-modulated structure enables one to adjust the location of multiple resonance frequencies simultaneously by varying an effective reflective position with frequency. That is, the IDTs are pitch-modulated so that the outer portion has slightly larger pitch than the inside, and the pitch of the outermost reflectors is made largest. Accordingly, higher-order SAW resonances occur between the two pitch-modulated IDTs. The outer portion of each IDT acts as a reflector, and the inner portion is mainly responsible for SAW excitation. Lower-order SAW resonances occur between the two reflectors.
authors.affiliation: Department of Electronics and Mechanical Engineering, Chiba University, Chiba 263-8522, Japan. k.hashimoto@ieee.org
authors.forename: Ken-ya
authors.initials: KY
authors.lastname: Hashimoto
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Omori
authors.forename: Masatsune
authors.initials: M
authors.lastname: Yamaguchi