US 5,331,247 AGranted

Surface acoustic wave device and communication device using the same

AssigneeHitachi, Ltd.

InventorsHiroaki Ikeda, Takashi Shiba, Osamu Hikino

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Abstract

In an interdigital electrode of a surface acoustic wave device having nonexciting portions formed by removing fingers, fingers having an excitation source located nearest to a nonexciting portion in between are so positioned as to approach the nonexciting portion as compared with arrangement pitch of other fingers. Fingers having an excitation source located nearest to an end of the electrode in between are so positioned as to approach the end of the interdigital electrode as compared with arrangement pitch of other fingers. Fingers having an excitation source located in the central portion of the electrode group in between are so positioned as to approach each other as compared with arrangement pitch of other fingers.

Claims14

Dependent claims

A surface acoustic wave device comprising a surface acoustic wave substrate and a pair of interdigital electrodes formed on said substrate, each of said electrodes having a bus bar and a plurality of electrode fingers extending from said bus bar generally perpendicular thereto and interdigitated with electrode fingers of the other electrode so that finger pairs are formed between adjacent electrode fingers extending from different bus bars, wherein:

at least one withdrawal weighting gap is provided with respect to said pair of interdigital electrodes on said substrate such that said electrode fingers of said pair of interdigital electrodes are divided into a plurality of electrode finger groups, and no finger exists in said gap to form a nonexciting portion in said surface acoustic wave device, each of said electrode finger groups including electrode fingers regularly arranged with a predetermined pitch, said withdrawal weighting gap of said nonexciting portion having a width as viewed in a surface acoustic wave propagating direction equal to a distance between one electrode finger and another electrode finger not adjacent to said one electrode finger in said regularly arranged electrode fingers, said nonexciting portion causing a distortion of distribution of an electric field to be generated by electrode fingers of said pair of interdigital electrodes when an electric voltage is applied across said bus bars with all of said electrode fingers of said pair of interdigital electrodes being arranged with said predetermined pitch;
and
at least one distortion cancelling finger pair being included in each of said electrode finger groups and being arranged such that a length between a central line between said distortion cancelling finger pair and a central line between a finger pair adjacent to said distortion cancelling finger pair is different from a length between central lines between other adjacent two finger pairs in said regularly arranged electrode fingers in said electrode finger groups to cancel said distortion of the electric field distribution, said central lines being viewed generally in a lengthwise direction of said electrode fingers.

at least one withdrawal weighting gap is provided with respect to said pair of interdigital electrodes on said substrate such that said electrode fingers of said pair of interdigital electrodes are divided into a plurality of electrode finger groups, and no finger exists in said gap to form a nonexciting portion in said surface acoustic wave device, each of said electrode finger groups including electrode fingers regularly arranged with a predetermined pitch, said withdrawal weighting gap of said nonexciting portion having a width as viewed in a surface acoustic wave propagating direction equal to a distance between one electrode finger and another electrode finger not adjacent to said one electrode finger in said regularly arranged electrode fingers, said nonexciting portion causing a distortion of distribution of an electric field to be generated by electrode fingers of said pair of interdigital electrodes when an electric voltage is applied across said bus bars with all of said electrode fingers of said pair of interdigital electrodes being arranged with said predetermined pitch;
and
each of two centrally located electrode finger pairs centrally located in each of said electrode finger groups is arranged such that a length between a central line between said centrally located finger pair and a central line between a finger pair outwardly adjacent to said centrally located finger pair is smaller than a length between central lines between other adjacent two finger pairs in said regularly arranged electrode fingers in an associated electrode finger group to cancel said distortion of said electric field distribution, said central lines being viewed generally in a lengthwise direction of said electrode fingers.

Dependencies are inferred from the claim text.