Patent ID: 7369015

Claim:
A balanced surface acoustic wave filter having an unbalanced terminal and first and second balanced terminals and having a balanced-unbalanced conversion function, comprising: a piezoelectric substrate; and first to fifth IDTs arranged on the piezoelectric substrate along a surface acoustic wave propagation direction; wherein the second and fourth IDTs are connected to the unbalanced terminal, and the second IDT and the fourth IDT have a phase difference of 180° with respect to each other; the third IDT is divided into a first sub-IDT portion and a second sub-IDT portion along the surface acoustic wave propagation direction, the first sub-IDT portion and the first IDT are connected to the first balanced terminal, and the second sub-IDT portion and the fifth IDT are connected to the second balanced terminal; and conditions of 1.55≦N 3 /N 1 ≦2.58 and N 1 =N 5 are satisfied, where N 1 denotes the number of electrode fingers that determines the center frequency of the first IDT, N 3 denotes the number of electrode fingers that determines the center frequency of the third IDT, and N 5 denotes the number of electrode fingers that determines the center frequency of the fifth IDT.