DUAL TRACK TYPE ACOUSTIC SURFACE WAVE FILTER INCLUDING FIRST AND SECOND ACOUSTIC CHANNELS

摘要

PURPOSE: A dual track type acoustic surface wave filter including first and second acoustic channels is provided to increase steepness of the filter characteristic and suppress effectively out-of-band response. CONSTITUTION: A first acoustic channel includes a first input transducer(3a) and a first output transducer(3b). The first acoustic channel is weighted so as to define a first transfer function by the first input transducer and the first output transducer. A second acoustic channel(4) includes a second input transducer(4a) and a second output transducer(4b). The second acoustic channel is weighted to define a second transfer function by the second input transducer and the second output transducer. The first and second input transducers are electrically connected in parallel. The first and second output transducers are electrically connected in parallel. The first and second transfer functions are substantially in phase within a pass band and have substantially opposite phases outside the pass band. The bandwidth of the second acoustic channel is narrower than the bandwidth of the first acoustic channel. A first side lobe of the second transfer function of the second acoustic channel has a phase opposite to a phase of a main lobe of the first transfer function of the first acoustic channel.