Patent ID: 6972643

Claim:
A longitudinally coupled surface acoustic wave filter comprising: a piezoelectric substrate; and a plurality of interdigital transducer electrodes (IDT electrodes) and a plurality of reflector electrodes disposed on the piezoelectric substrate, wherein each of the IDT electrodes is an interdigital electrode including a plurality of opposed electrode fingers, wherein the IDT electrodes and the reflector electrodes are arranged in close relation along a propagation direction of a surface acoustic wave, wherein each of the IDT electrodes includes a primary excitation region having λ/2 electrode finger pitches, where λ is a wavelength of the surface acoustic wave, wherein the primary excitation region of at least one of the IDT electrodes is phase-shifted from the primary excitation region of another IDT electrode by a certain amount in accordance with a desired passband frequency response, and wherein at least one of a condition that at least one of the IDT electrodes includes, on a side thereof adjacent to another IDT electrode, a secondary excitation region having electrode finger pitches different from the λ/2 pitches, and a condition that at least one of the reflector electrodes having electrode finger pitches different from the λ/2 pitches is disposed between two of the IDT electrodes is established, the plurality of IDT electrodes includes a first IDT electrode and a second IDT electrode adjacent to the first IDT electrode, the reflector electrodes include a first reflector electrode adjacent to the first IDT electrode and a second reflector electrode adjacent to the second IDT electrode, the respective primary excitation regions of the first and second IDT electrodes are phase-shifted from each other by the certain amount in accordance with the desired passband frequency response, and the first and second IDT electrodes include, on the respective adjacent sides of the first and second IDT electrodes, respective secondary excitation regions each having the electrode finger pitches different from the λ/2 pitches, wherein the electrode finger pitches of at least one of the secondary excitation regions are all equal.