A surface acoustic wave filter includes a first reflector, a first IDT, a
second IDT, a third IDT, and a second reflector arranged in that order on
a piezoelectric substrate. The first IDT and the third IDT, connected in
parallel, are together also connected to an unbalanced signal terminal.
The second IDT includes two separate comb-like electrodes arranged in the
direction of propagation of a surface acoustic wave, and electrically
connected in series to each other at a serial junction. The comb-like
electrodes are respectively connected to balanced signal terminals. The
outermost electrode finger of the first IDT is connected to the unbalanced
signal terminal, and the outermost electrode finger of the third IDT is
grounded. The first IDT only or both the first IDT and the third IDT are
weighted so that the number of excitation regions of the surface acoustic
wave between the second IDT and the first IDT becomes equal to the number
of excitation regions of the surface acoustic wave between the second IDT
and the third IDT.
