US Patent No. 9,450,564

ELASTIC WAVE FILTER


Patent No. 9,450,564
Issue Date September 20, 2016
Title Elastic Wave Filter
Inventorship Ryuji Kajihara, Saitama (JP)
Assignee NIHON DEMPA KOGYO CO., LTD., Tokyo (JP)

Claim of US Patent No. 9,450,564

1. An elastic wave filter, comprising:
a piezoelectric substrate;
an input side interdigital transducer (IDT) electrode that includes a pair of busbars and an electrode finger, the pair of
busbars being arranged so as to be separated from one another in a direction perpendicular to a propagation direction of an
elastic wave on the piezoelectric substrate, the electrode finger each extending from each of the pair of busbars toward an
opposed busbar in a comb shape;

an output side IDT electrode that includes a pair of busbars and an electrode finger, the pair of busbars being disposed at
positions separating in the propagation direction of the elastic wave with respect to the input side IDT electrode, the pair
of busbars being arranged so as to be separated from one another in the direction perpendicular to the propagation direction
of the elastic wave on the piezoelectric substrate, the electrode finger each extending from each of the pair of busbars toward
an opposed busbar in a comb shape; and

a reflector that includes a pair of reflector busbars and a reflector electrode finger, when viewed from a line arrangement
of the input side IDT electrode and the output side IDT electrode, the respective pair of reflector busbars being arranged
at one side and another side in the propagation direction of the elastic wave, the pair of reflector busbars being disposed
so as to be separated from one another in the direction perpendicular to the propagation direction of the elastic wave, the
reflector electrode finger connecting between the reflector busbars, wherein:

assuming that a length dimension at which the electrode fingers adjacent to one another intersect is referred to as an intersection
length, at least one IDT electrode among the input side IDT electrode and the output side IDT electrode is weighted only with
a main lobe among an apodized weighting method, such that the intersection length becomes short from a part at which one electrode
finger is opposed to another electrode finger adjacent to the one electrode finger toward an end portion of the at least one
IDT electrode in the propagation direction of the elastic wave, and

a part with the largest intersection length in the at least one IDT electrode is shifted to any one of one side and another
side in the propagation direction of the elastic wave from a center position at the at least one IDT electrode in the propagation
direction of the elastic wave,

wherein the input side IDT electrode and the output side IDT electrode are each weighted with the apodized main lobe,
when viewed from one reflector among the pair of reflectors, the part with the largest intersection length at the input side
IDT electrode is disposed at a position shifted to one side from the center position at the input side IDT electrode in the
propagation direction of the elastic wave, and

when viewed from the one reflector, the part with the largest intersection length at the output side IDT electrode is disposed
at a position shifted to the one side from the center position at the output side IDT electrode in the propagation direction
of the elastic wave.