Surface acoustic wave filter, surface acoustic wave filter device, and duplexer including a shared reflector

A surface acoustic wave filter comprising:

• a piezoelectric substrate;
• a longitudinally coupled resonator first filter section provided on the piezoelectric substrate;
• and
• a longitudinally coupled resonator second filter section that is electrically connected to the first filter section in parallel or in series on at least one of an input signal side and an output signal side and that is provided on the piezoelectric substrate next to the first filter section in a surface acoustic wave propagation direction;
• wherein
• the first filter section includes a first interdigital transducer group including a plurality of interdigital transducers arranged in the surface acoustic wave propagation direction and a pair of first reflectors disposed on each side of the first interdigital transducer group in the surface acoustic wave propagation direction;
• the second filter section includes a second interdigital transducer group including a plurality of interdigital transducers arranged in the surface acoustic wave propagation direction and a pair of second reflectors disposed on each side of the second interdigital transducer group in the surface acoustic wave propagation direction;
• the first reflector and the second reflector disposed between the first interdigital transducer group and the second interdigital transducer group are defined by an integrated shared reflector;
• a number of electrode fingers in reflecting units in the integrated shared reflector is an odd number of no less than nine;
• and
• the integrated shared reflector is located such that a distance between centers of two adjacent electrode fingers in the surface acoustic wave propagation direction is half of a wave length of the surface acoustic wave determined by a pitch of electrode fingers of the interdigital transducers.

A surface acoustic wave filter comprising:

• a piezoelectric substrate;
• a longitudinally coupled resonator first filter section provided on the piezoelectric substrate;
• and
• a longitudinally coupled resonator second filter section that is electrically connected to the first filter section in parallel or in series on at least one of an input signal side and an output signal side and that is provided on the piezoelectric substrate next to the first filter section in a surface acoustic wave propagation direction;
• wherein
• the first filter section includes a first interdigital transducer group including a plurality of interdigital transducers arranged in the surface acoustic wave propagation direction and a pair of first reflectors disposed on each side of the first interdigital transducer group in the surface acoustic wave propagation direction;
• the second filter section includes a second interdigital transducer group including a plurality of interdigital transducers arranged in the surface acoustic wave propagation direction and a pair of second reflectors disposed on each side of the second interdigital transducer group in the surface acoustic wave propagation direction;
• the first reflector and the second reflector disposed between the first interdigital transducer group and the second interdigital transducer group are defined by an integrated shared reflector;
• a number of electrode fingers in reflecting units in the integrated shared reflector is an odd number of no less than nine;
• and
• the integrated shared reflector is configured such that dimensions of the electrode fingers thereof arranged in the surface acoustic wave propagation direction and an interval between the electrode fingers thereof in the surface acoustic wave propagation direction are each about λ/4, where λ is a wavelength of a surface acoustic wave that propagates in the surface acoustic wave propagation direction.