Filter device with sharp attenuation characteristic in narrow bandwidth and branching filter using the same

摘要

In a filter device (10) constituted by circuit elements formed on a single substrate (11), the circuit elements include a first wiring section (14) formed between an input signal electrode (12) and an output signal electrode (13), first resonators (15a,15b,15c) located in the first wiring section (14) and having a predetermined resonance frequency, second wiring sections (17a,17b,17c,17d) formed between the first wiring section (14) and a ground electrode (16), second resonators (18a,18b,18c,18d) located in the second wiring sections (17a,17b,17c,17d) and having an anti-resonance frequency forming a pass-band with the predetermined resonance frequency of the first resonators (15a,15b,15c). An effective electric and mechanical coupling factor of the second resonator (18a) is different from those of the other resonators (15a,15b,15c,18b,18c,18d).