Surface acoustic wave band-pass filter with different phase weighted transducers

Claim 1

In a surface acoustic wave band-pass filter comprising a surface acoustic wave propagating substrate, a first surface acoustic wave device disposed on said substrate, a second surface acoustic wave device disposed on said substrate, said first and second surface acoustic wave devices are symmetrically arranged about a line therebetween and a propagating direction of a surface acoustic wave being parallel to said line, said first surface acoustic wave device including a first electro-acoustic transducer unit divided in the surface wave propagating direction into a plurality of repetitively arranged first electro-acoustic transducers, said plurality of first electro-acoustic transducers being connected commonly to an input electric signal source for converting said input electric signal to a first surface acoustic wave, and said first surface acoustic wave device including a first acousto-electric transducer unit having a plurality of first acousto-electric transducers arranged repetitively and alternatively to said first electro-acoustic transducers for receiving said first surface acoustic wave emitted from said first electro-acoustic transducers and converting said first surface acoustic wave into an intermediate electric signal, said second surface acoustic wave device including a second acousto-electric transducer unit divided in the surface acoustic wave propagating direction into a plurality of repetitively arranged second acousto-electric transducers, said plurality of second acousto-electric transducers being connected commonly to an output terminal, and said second surface acoustic wave device including a second electro-acoustic transducer unit having a plurality of second electro-acoustic transducers arranged repetitively and alternatively to said second acousto-electric transducers and correspondingly electrically connected to said plurality of first acousto-electric transducers of said first acousto-electric transducer unit for converting said intermediate electric signal from said first acousto-electric transducer unit into a second surface acoustic wave and emitting said second surface acoustic wave to said second acousto-electric transducer unit which provides an output electric signal at said output terminal, an improvement comprising: at least one of a first acousto-electric transducer and a correspondingly electrically connected second electro-acoustic transducer being phase-weighted differently from each other and each said first acousto-electric transducer and said second electro-acoustic transducer being respectively phased weighted differently from other transducers of the same type on the same device.