Operation mechanism of double-mode surface acoustic wave filters with pitch-modulated IDTs and reflectors.
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.
Hashimoto
Ken-ya
KY
Department of Electronics and Mechanical Engineering, Chiba University, Chiba 263-8522, Japan. k.hashimoto@ieee.org
Omori
Tatsuya
T
Yamaguchi
Masatsune
M