| 摘要 |
In a surface acoustic wave filter having a piezoelectric substrate (11) on which an input interdigital transducer (12) and first and second output interdigital transducers (15, 16) are disposed with the output interdigital transducers opposed to the input interdigital transducer apart therefrom, a first output port (17) for the first output interdigital transducer is directly connected to a filter output terminal (20). Between the filter output terminal and a second output port (18) for the second output interdigital transducer, a switch (22) selectively connects the second output port to the filter output terminal to make the filter output terminal produce a filtered output signal which is equal to a sum of at least one of output electric signals supplied from the first and the second output ports. The switch may be a PIN diode or a mechanical switch. The input interdigital transducer may be divided into a plurality of partial input interdigital transducers for supplying a surface acoustic wave to the output interdigital transducers, respectively. The first output interdigital transducer has a primary weighting factor while the second output interdigital transducer has a difference weighting factor.
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