Surface acoustic wave filter device

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 N1 and P1, respectively, the number of electrode fingers and electrode finger pitch of the second and third IDTs are represented by N2 and P2, respectively, and the number of electrode fingers and electrode finger pitch of the fourth and fifth IDTs are represented by N3 and P3, 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 N1<N2, N1<N3, P1<P2, and P1<P3.