Patent ID: 7439827

Claim:
A longitudinally-coupled-resonator surface acoustic wave filter device comprising: a piezoelectric substrate; a first IDT disposed on the piezoelectric substrate; second and third IDTs arranged on either side of the first IDT in a direction of propagation of surface waves; fourth and fifth IDTs arranged on either side of a portion in the direction of propagation of surface waves where the first to third IDTs are disposed; and first and second reflectors arranged on either side of a portion in the direction of propagation of surface waves where the first to fifth IDTs are disposed; wherein when the number of electrode fingers and electrode finger pitch of the first IDT are represented by N 1 and P 1 , respectively, the number of electrode fingers and electrode finger pitch of the second and third IDTs are represented by N 2 and P 2 , respectively, and the number of electrode fingers and electrode finger pitch of the fourth and fifth IDTs are represented by N 3 and P 3 , respectively, the numbers of electrode fingers and electrode finger pitches of the first to fifth IDTs are determined so as to satisfy a relationship of N 1 <N 2 , N 1 <N 3 , P 1 <P 2 , and P 1 <P 3 .