A surface acoustic wave filter apparatus includes extensional-coupling-resonator-mode
first through fourth SAW filter devices which are disposed on a piezoelectric substrate.
Each SAW filter device includes three interdigital transducers (IDTs) arranged
in a SAW propagating direction, and reflectors arranged such that they sandwich
the IDTs therebetween. The SAW filter devices have a balanced-to-unbalanced input/output
function. The reflectors of the first and second SAW filter devices are different
from those of the third and fourth SAW filter devices in at least one of the number,
the pitch, the duty, and the thickness of the electrode fingers of the reflectors.
