Surface acoustic wave (SAW) resonator, SAW filter and SAW antenna duplexer using the SAW resonator

1. A surface acoustic wave (SAW) resonator comprising:

a piezoelectric substrate:

an interdigital transducer (IDT) electrode formed on said piezoelectric substrate; and

a reflector electrode disposed adjacent to said IDT electrode;

wherein said IDT electrode comprises:

a plurality of first finger-electrodes;

a plurality of second finger-electrodes;

a plurality of strip-line electrodes;

a first bus-bar electrode coupled to said first finger-electrodes; and

a second bus-bar electrode coupled to said second finger-electrodes;

wherein said first finger-electrodes and said second finger-electrodes do not overlap with each other, but are acoustically coupled together by said strip-line electrodes,

wherein said strip-line electrodes overlap with at least one of said first finger-electrodes and said second finger-electrodes,

wherein said IDT electrode and said reflector electrode form at least two resonating units,

wherein said at least two resonating units are coupled in series via said strip-line electrodes,

wherein said IDT electrode further comprises a plurality of dummy electrodes respectively disposed between said first finger-electrodes and said second finger-electrodes such that each of said dummy electrodes faces a respective one of said strip-line electrodes, and

wherein each of said dummy electrodes has a width greater than that of each of said first finger-electrodes and that of each of said second finger-electrodes.

2. The SAW resonator of claim 1 , wherein said first finger-electrodes and said second finger-electrodes are arranged in a face-to-face manner.

3. The SAW resonator of claim 1 ,

wherein said first finger-electrodes are respectively arranged at intervals of a propagation wavelength of the SAW,

wherein said second finger-electrodes are respectively arranged at intervals of a propagation wavelength of the SAW, and

wherein said first finger-electrodes are arranged to directly face said second-finger electrodes along a propagating direction of the SAW.

4. The SAW resonator of claim 3 , wherein said strip-line electrodes are disposed with a deviation of λ/2, where λ=a wavelength of the SAW, from respective centers of said first finger-electrodes and said second finger-electrodes.

5. The SAW resonator of claim 4 ,

wherein a first area, where said first finger-electrodes and said strip-line electrodes overlap with each other, forms a first resonating unit, and

wherein a second area, where said second finger-electrodes and said strip-line electrodes overlap with each other, forms a second resonating unit.

6. The SAW resonator of claim 1 ,

wherein said first finger-electrodes are respectively arranged at intervals of a propagation wavelength of the SAW,

wherein said second finger-electrodes are respectively arranged at intervals of a propagation wavelength of the SAW, and

wherein said first finger-electrodes and said second finger-electrodes are respectively arranged to face each other and to deviate from each other by a given distance along a propagation direction of the SAW.

7. The SAW resonator of claim 6 , wherein the given distance is one of λ/2 and λ/4, where λ is the propagation wavelength of the SAW.

8. The SAW resonator of claim 6 , wherein said strip-line electrodes are separated from said first finger-electrodes and said second finger-electrodes respectively with substantially equal spaces in between, and wherein each one of said strip-line electrodes is shaped like a dogleg.

9. The SAW resonator of claim 1 , wherein each of said dummy electrodes has a length of not less than λ/2, where λ=a wavelength of the SAW.

10. The SAW resonator of claim 1 , wherein each of said dummy electrodes faces a respective one of said strip-line electrodes with a space in-between of not more than λ/4, where λ=a wavelength of the SAW.

11. A surface acoustic wave (SAW) filter comprising:

a piezoelectric substrate;

a plurality of interdigital transducer (IDT) electrodes disposed on said piezoelectric substrate adjacent to each other along a propagating direction of the SAW;

a first reflector electrode disposed at a first side of said plurality of IDT electrodes; and

a second reflector electrode disposed at a second side of said plurality of IDT electrodes,

wherein at least one of said IDT electrodes includes a first finger-electrode, a second finger-electrode and a strip-line electrode, and

wherein said first finger-electrode and said second finger-electrode do not overlap with each other but are acoustically coupled together by said strip-line electrode.

12. The SAW filter of claim 11 , wherein said plurality of IDT electrodes includes a first IDT electrode, a second IDT electrode, and a third IDT electrode,

wherein said second IDT electrode is disposed between said first IDT electrode and said third IDT electrode, and includes said first finger-electrode, said second finger-electrode and said strip-line electrode,

wherein said first finger-electrode and said second finger-electrode do not overlap with each other but are acoustically coupled together by said strip-line electrode,

wherein each of said first IDT electrode and said third IDT electrode are formed of two IDT electrode patterns coupled together in parallel.