Patent ID: 7501917

Claim:
A SAW filter comprising: a piezoelectric substrate; a first inter-digital transducer having a first comb-shaped electrode with electrode fingers, disposed along a surface acoustic wave propagation path on said piezoelectric substrate, said first inter-digital transducer having a resonance frequency and being connected serially in a signal path; a second inter-digital transducer having a second comb-shaped electrode with electrode fingers, disposed in proximity to said first inter-digital transducer and along the surface acoustic wave propagation path, said second inter-digital transducer being connected between the signal path and a ground, having a resonance frequency different from said resonance frequency of said first inter-digital transducer; a first reflector electrode disposed on an outermost side of said first inter-digital transducer; a second reflector electrode disposed on an outermost side of said second inter-digital transducer; and a strip line electrode disposed between said first inter-digital transducer and said second inter-digital transducer so that said electrode fingers of said first inter-digital transducer, said strip line electrode, and said electrode fingers of said second inter-digital transducer are arranged almost continuously; wherein an electrode finger of said electrode fingers of said first inter-digital transducer that is the closest to said second inter-digital transducer and an electrode finger of said electrode fingers of said second inter-digital transducer that is the closest to said first inter-digital transducer determine peaks and troughs of surface acoustic waves along said surface acoustic surface wave propagation path, wherein said first comb-shaped electrode and said second comb-shaped electrode are connected, wherein a polarity of said first inter-digital transducer and a polarity of said second inter-digital transducer fall in reversed phases from each other relative to surface acoustic waves along said surface acoustic wave propagation path, and wherein a pitch of said electrode fingers of said strip line electrode is between a pitch of said electrode fingers of said first inter-digital transducer and a pitch of said electrode fingers of said second inter-digital transducer.