US 3,987,379 AGranted

Acoustic surface wave filter having combined split-isolated and split-connected coupler

AssigneeZenith Radio Corporation

InventorAdrian J. DeVries

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Abstract

An acoustic surface wave filter has offset transmitting and receiving transducers formed on the wave propagating surface of a piezoelectric substrate. A two-segment multistrip coupler is interposed on the propagating surface and provides "track switching" or "sidestepping" action for signals within the coupler passband. The coupler includes a split-connected portion formed by electrically connected filamentary conductor pairs and a split-isolated portion formed by electrically continuous filamentary conductors and interleaved conductors having a discontinuity at their center. The split-connected portion attenuates the symmetrical mode components of acoustic waves within the coupler stop band while the split-isolated portion attenuates the anti-symmetrical mode portion of acoustic waves within the coupler stop band, producing an improved trap response.

Claims7

Dependent claims

An acoustic surface wave filter having a transfer characteristic including a passband and a stop band comprising:

a piezoelectric substrate defining a wave propagating surface;
transmitting and receiving transducer means formed on said surface for launching and receiving acoustic surface waves via a propagation path, said waves resolvable into symmetrical and anti-symmetrical mode components;
a multistrip coupler formed on said surface interposed between said transducer means within said wave propagation path including first coupling means substantially attenuating the symmetrical mode component while coupling the anti-symmetrical mode component of signals within said stop band unattenuated and second coupling means substantially attenuating the anti-symmetrical mode component while coupling the symmetrical mode component of signals within said stop band unattenuated, said first and second coupling means being arranged serially in said propagation path.

Dependencies are inferred from the claim text.