Low-loss acoustic wave filter device

Details Low-loss acoustic wave filter device Low-loss acoustic wave filter device

1983-05-12

1985-04-23

Nussbaum, Marvin L.

Wave transmission lines and networks

Coupling networks

Electromechanical filter

310313C, 333151, 333154, 333196, H03H 9145, H03H 964

Patent

active

045132615

ABSTRACT:
An acoustic wave filter device with low loss and low passband ripple characteristics. The filter comprises three bidirectional electroacoustical transducers disposed along a common axis on the surface of a substrate of piezoelectric material. The two outer transducers of the three function as input transducers and the center transducer functions as an output transducer. One of the input transducers is of the antisymmetric type and has a transfer characteristic that differs in phase angle by ninety degrees with respect to the other input transducer, which is of the symmetric type. This ninety-degree difference applies at all frequencies, so that any energy reflected from the output transducer and again reflected by an input transducer will be subject to a phase shift of 180 degrees in the case of energy reflected from the antisymmetric input transducer, and no phase shift in the case of the symmetric input transducer. Accordingly, these triple-transit echoes will cancel at the output transducer, for all frequencies. For the primary energy propagation from the input transducers to the output transducer, a ninety-degree phase shifter in one input circuit ensures that the signals from the two input transducers are in phase when they reach the output transducer.

REFERENCES:
patent: 3859608 (1975-01-01), Hartmann et al.
patent: 3908137 (1975-09-01), Hunsinger et al.
patent: 4044321 (1977-08-01), Vasile
patent: 4237432 (1980-12-01), Huang et al.

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