A surface acoustic wave filter device, having a balanced-to-unbalanced
conversion function, in which input/output impedances are different and in
which the in-band degree of balance is satisfactory, is obtained. The
surface acoustic wave filter device has a balanced-to-unbalanced
conversion function, in which the spacing of input/output IDTs of a second
surface acoustic wave filter element is larger by approximately half the
wavelength of the surface-acoustic wave than that of a first surface
acoustic wave filter element so that the phase is inverted, wherein the
total of the electrostatic capacitance values of a plurality of IDTs of
the second surface acoustic wave filter element is larger than the total
of the electrostatic capacitance values of a plurality of IDTs of the
first surface acoustic wave filter element.
