| 摘要 |
PROBLEM TO BE SOLVED: To obtain an easily manufacturable band-pass type surface acoustic wave(SAW) filter capable of enhancing steepness in filter property between the passband and the stopband. SOLUTION: The filter has a ladder-type circuit comprising series arm resonators 4, 6 connected between input and output terminals IN, OUT and parallel arm resonators 3, 5, 7 connected between the series arm resonators and a reference potential, where the antiresonant frequencies of the parallel arm resonators 3, 5, 7 are substantially matched with the resonant frequencies of the series arm resonators 4, 6. In addition, the antiresonant frequency of at least one of the parallel arm resonators 3 is set to be inside the stop band of reflectors 3b, 3c and the spurious component is set outside the stopband to obtain the steepness in filter property from the passband to the stopband.
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