Surface acoustic wave filter

• US 4,263,571 A
• Filed: 11/15/1979
• Issued: 04/21/1981
• Est. Priority Date: 11/15/1978
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Hikita, Mitsutaka, Kinoshita, Yasuaki
• Primary Examiner(s): Nussbaum, Marvin L.
• Application Number:
  US06/094,736
• Time in Patent Office: 523 Days
• Field of Search: 333/150-155, 333/193-196, 331/107 A, 310/313
• US Class Current: 333/194
• CPC Class Codes: H03H 9/6496 Reducing ripple in transfer characteristic

Abstract

A broad-band surface acoustic wave filter of turn reflector type in which the number N of thin film finger or stripe electrode pairs in at least one transducer is selected to satisfy N=F/k² to obtain a flat selected band in the frequency response, where F is the constant determined by the material of the used piezo-electric substrate and "k² " is the electro-mechanical coupling coefficient.

Claims

1. A turn reflector type of surface acoustic wave filter comprising a transmitting transducer having a group of thin film finger or stripe electrodes on the surface of a piezo-electric substrate for converting a first electric signal to a surface acoustic wave, a receiving transducer having a group of thin film finger or stripe electrodes on the substrate for converting said surface acoustic wave to a second electric signal, and reflectors provided at both sides of said transmitting and receiving transducers;

wherein the number N of the thin film finger electrode pairs in at least one of said transmitting and receiving transducers is selected so as to satisfy N≅

F/k², where F is the constant determined by the material of said substrate and "k² " is the electro-mechanical coupling coefficient.

2. The turn reflector type of surface acoustic wave filter as defined in claim 1 wherein said piezo-electric substrate is of lithiumniobate Y-cut propagation and said constant F determined by the substrate material is selected to be 1.5.

3. The turn reflector type of surface acoustic wave filter as defined in claim 1 wherein 3 dB directional couplers are provided between said transmitting and receiving transducers and said reflectors.

4. The turn reflector type of surface acoustic wave filter as defined in claim 1 wherein said each reflector consists of a plurality of grooves cut at a 45°

angle with respect to the length of the stripe electrodes in said transmitting and receiving transducers.