Surface acoustic wave filter device and duplexer

A surface acoustic wave filter device comprising:

• a piezoelectric substrate;
• a first surface acoustic wave filter provided on the piezoelectric substrate;
• and
• a second surface acoustic wave filter provided on the piezoelectric substrate;
• wherein
• the first surface acoustic wave filter includes a longitudinally coupled resonator-type first filter section and a longitudinally coupled resonator-type second filter section, the second filter section being electrically connected in parallel or series with the first filter section on at least one of an input signal side and an output signal side;
• the first filter section includes a first interdigital transducer (IDT) group including three IDTs arranged in a line in a surface acoustic wave propagation direction and a pair of first reflectors arranged on either side of the first IDT group in the surface acoustic wave propagation direction;
• the second filter section includes a second IDT group including three IDTs arranged in a line in the surface acoustic wave propagation direction and a pair of second reflectors arranged on either side of the second IDT group in the surface acoustic wave propagation direction;
• the second surface acoustic wave filter includes a third IDT group that is cascade connected to the first filter section and the second filter section and includes a first IDT, a second IDT, a third IDT, a fourth IDT, and a fifth IDT arranged in order in a line in the surface acoustic wave propagation direction, and a pair of third reflectors arranged on either side of the third IDT group in the surface acoustic wave propagation direction;
• the second IDT and the fourth IDT of the third IDT group are connected together to one of an input terminal and an output terminal;
• a first wiring line connects the first IDT of the third IDT group to a first IDT of the first IDT group;
• a second wiring line connects the third IDT of the third IDT group to a third IDT of the first IDT group;
• the first wiring line and the second wiring line are opposite to each other in phase;
• a third wiring line connects the third IDT of the third IDT group to a first IDT of the second IDT group;
• a fourth wiring line connects the fifth IDT of the third IDT group to a third IDT of the second IDT group;
• the third wiring line and the fourth wiring line are opposite to each other in phase;
• a second IDT of the first IDT group and a second IDT of the second IDT group are connected together to one of the output terminal and the input terminal;
• and
• an integrated common reflector defines one of the pair of first reflectors and one of the pair of second reflectors.