Patent ID: 6353371
Filing Date: 2002-03-05
Classification: H03H

Abstract:
A transversely coupled resonator type surface acoustic wave filter comprising:a surface acoustic wave substrate having opposing first and second end surfaces; and first and second surface acoustic wave resonators on the surface acoustic wave substrate, and which are arranged to generate a surface acoustic wave having an SH wave as a main component, the first and second surface acoustic wave resonators being coupled to define a stage of the transversely coupled resonator filter; wherein the first and second surface acoustic wave resonators include first and second interdigital transducers, the first and second interdigital transducers defined by a first bus bar, a second bus bar and a common bus bar all arranged so as to be substantially parallel to each other and extending in a direction of transmission of the surface acoustic wave, the common bus bar is located between the first and second bus bars, and a plurality of electrode fingers are connected to the first and second bus bars at a first end of the electrode fingers and extended towards the common bus bar, a plurality of electrode fingers are connected to the common bus bar at a first end of the electrode fingers and such that a first set of electrode fingers of the common bus bar are extended towards the first bus bar and a second set of electrode fingers are extended towards the second bus bar so that the first and second sets of electrode fingers of the common bus bar interdigitate with the electrode fingers of the first and second bus bars, respectively; wherein the surface acoustic wave substrate has a relative dielectric constant E such that E=âˆˆs11/âˆˆ0, and where E is in a range of about 0 to about 3000; an aperture y of the interdigital transducer is defined as an amount of overlap between the electrode fingers of the common bus bar with the electrode fingers of the first and second bus bars normalized by a wavelength &lgr; of the surface acoustic wave; and the filter is constructed such that y satisfies a formula: 0.945+5.49Ã—exp(âˆ’E/366)&gE;y&gE;2.46Ã—exp(âˆ’E/219)â€ƒâ€ƒ(1).