| CPC H03H 9/568 (2013.01) [H03H 9/133 (2013.01); H03H 9/173 (2013.01)] | 21 Claims |
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1. An acoustic wave filter comprising:
a plurality of series resonators;
a plurality of shunt resonators disposed between the series resonators and a ground, at least one shunt resonator of the plurality of shunt resonators including a substrate and a pair of interdigital transducer (IDT) electrodes disposed on the substrate, each of the IDT electrodes including a bus bar and a plurality of fingers extending from the bus bar, fingers of one IDT electrode arranged interleaved with respective fingers of the other IDT electrode, the plurality of fingers of the pair of IDT electrodes including a first group of fingers located at a center region of the pair of IDT electrodes and a second group of fingers located at edge regions on both sides of the center region, the first group of fingers having an average pitch distance shorter than an average pitch distance of the second group of fingers such to improve a response at a rejection band of the acoustic wave filter, the at least one shunt resonator being configured to induce a longitudinal mode response formed by waves confined in a resonant cavity of the acoustic wave filter, such to increase a bandwidth of the rejection band of the acoustic wave filter; and
a dielectric film formed to cover at least a part of the substrate and the pair of IDT electrodes.
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