Surface wave acoustic device with compensation for spurious frequency response modes

A surface acoustic wave device of the type having electrical input terminal means, primary acoustic wave sending means defining a primary wave propagation path, means coupling said primary sending means to said input terminal means, electrical output terminal means, primary acoustic wave receiving means defining a primary wave reception path offset from said propagation path, means coupling said primary receiving means to said output terminal means, and acoustic wave coupling means for offsetting a wave from said propagation path to said reception path, said primary receiving means being arranged to develop an electrical output across said output terminal means in response to said offset wave, said primary sending and receiving means being undesirably coupled to each other by a spurious wave propagated toward said primary receiving means by said primary sending means along a path other than said primary propagation path, the frequency response of said primary receiving means to said spurious wave being different from its frequency response to said offset wave;

• wherein the improvement comprises:
• auxiliary wave sending means coupled to said input terminal means and adapted to propagate an auxiliary wave;
• auxiliary wave receiving means coupled to said output terminal means and arranged to receive said auxiliary wave;
• said auxiliary receiving means being arranged to have a frequency response to said auxiliary wave which is similar to the frequency response of said primary receiving means to said spurious wave, and to develop an electrical output signal across said output terminal means in response to said auxiliary wave which is substantially opposite in phase to the output signal developed thereacross in response to said spurious wave by said primary receiving means, whereby to compensate at least partially for the effect of said spurious wave upon said primary receiving means.

A surface acoustic wave device of the type having a substrate of piezoelectric material, a primary acoustic wave sending interdigital transducer on a surface of said substrate defining an orthogonal acoustic wave propagation path, a primary acoustic wave receiving interdigital transducer on said substrate surface defining an orthogonal acoustic wave reception path offset from said propagation path, and multi-strip acoustic wave coupling means for offsetting a wave from said propagation path to said reception path, said primary sending and receiving transducers being undesirably coupled to each other by a diffracted signal propagated toward said primary receiving transducer by said primary sending transducer along a path at a substantial angle to said orthogonal paths, the frequency response of said primary receiving transducer to said diffracted wave being different from its frequency response to said offset wave;

• wherein the improvement comprises:
• an auxiliary acoustic wave sending interdigital transducer on said substrate surface;
• an auxiliary acoustic wave receiving interdigital transducer on said substrate surface, acoustically coupled to said auxiliary sending transducer;
• at least one of said auxiliary transducers being apodized in such manner that the frequency response of said auxiliary transducers is similar to the frequency response of said primary receiving transducer to said diffracted wave;
• means on said substrate surface electrically coupling said primary and auxiliary sending transducers so that the acoustic wave output of said auxiliary sending transducer is related to said diffracted wave;
• the interdigitated finger pairs of said auxiliary sending and receiving transducers being so positioned relative to those of said primary sending and receiving transducers that the electrical output of said auxiliary receiving transducer developed in response to said auxiliary sending transducer is substantially out of phase with the electrical output of said primary receiving transducer developed in response to said diffracted wave;
• and means on said substrate surface electrically coupling said primary and auxiliary receiving transducers whereby said out-of-phase output at least partially cancels said diffracted wave output.