Patent ID: 8736402

Claim:
An elastic wave filter device comprising: a piezoelectric substrate; and a longitudinally-coupled resonator-type elastic wave filter section including first to third IDT electrodes, which are successively arranged on the piezoelectric substrate in a direction of propagation of elastic waves and each of which includes a plurality of electrode fingers, and first and second reflectors arranged on the piezoelectric substrate respectively on both sides of a region in which the first to third IDT electrodes are disposed, as viewed in the direction of propagation of the elastic waves; wherein each of the first to third IDT electrodes includes a narrower-pitch portion provided in an end portion thereof, which is adjacent to another one of the first to third IDT electrodes in the direction of propagation of the elastic waves, the narrower-pitch portion having a smaller period of electrode fingers than a period of electrode fingers in a remaining portion of the respective one of the first to third IDT electrodes; a number of electrode fingers in the narrower-pitch portion of the second IDT electrode, which is disposed on a side closer to the first IDT electrode, and a number of electrode fingers in the narrower-pitch portion of the second IDT electrode, which is disposed on a side closer to the third IDT electrode, differ from each other; and the narrower-pitch portions of the first to third IDT electrodes are arranged such that a frequency of an attenuation pole generated due to a 1st-order resonance mode of the longitudinally-coupled resonator-type elastic wave filter section is located within a transient band which is positioned between a pass band and a stop band of the longitudinally-coupled resonator-type elastic wave filter section.