Surface acoustic wave filter
First Claim
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1. A surface acoustic wave filter comprising:
- a piezoelectric substrate;
a longitudinally coupled resonator filter provided on the piezoelectric substrate, said longitudinally coupled resonator filter including at least three interdigital transducers arranged along a surface acoustic wave propagation direction, at least one of the at least three interdigital transducers has a different phase from the other interdigital transducers;
an unbalanced terminal and a balanced terminal which are provided for the longitudinally coupled resonator filter; and
reflectors arranged to sandwich the at least three interdigital transducers therebetween in the longitudinally coupled resonator filter, each of said reflectors being grounded.
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Abstract
A surface acoustic wave filter unit having three interdigital transducers arranged along the surface acoustic wave propagation direction is disposed on a piezoelectric substrate. An unbalanced signal terminal and balanced signal terminals are provided for the surface acoustic wave filter unit. At least one of the three interdigital transducers is out of phase relative to the other interdigital transducers. Reflectors are arranged so as to sandwich the three interdigital transducers therebetween. The reflectors are grounded. Thus, a surface acoustic wave filter having a balance-to-unbalance conversion function and having high balance between the balanced signal terminals is achieved.
26 Citations
21 Claims
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1. A surface acoustic wave filter comprising:
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a piezoelectric substrate;
a longitudinally coupled resonator filter provided on the piezoelectric substrate, said longitudinally coupled resonator filter including at least three interdigital transducers arranged along a surface acoustic wave propagation direction, at least one of the at least three interdigital transducers has a different phase from the other interdigital transducers;
an unbalanced terminal and a balanced terminal which are provided for the longitudinally coupled resonator filter; and
reflectors arranged to sandwich the at least three interdigital transducers therebetween in the longitudinally coupled resonator filter, each of said reflectors being grounded. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A surface acoustic wave filter comprising:
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a piezoelectric substrate;
a plurality of longitudinally coupled resonator filters provided on the piezoelectric substrate, each filter including at least three interdigital transducers arranged along a surface acoustic wave propagation direction, at least one of the at least three interdigital transducers has a different phase from the other interdigital transducers;
an unbalanced terminal and a balanced terminal which are provided for the plurality of longitudinally coupled resonator filters; and
reflectors arranged to sandwich the at least three interdigital transducers therebetween in each of the longitudinally coupled resonator filters, each of said reflectors being grounded. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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Specification