Patent ID: 8330558

Claim:
A ladder type filter comprising: series resonators; one or more parallel resonators; a first resonator; a second resonator in which an excitation efficiency is reduced more than the first resonator; and an inductor connected in parallel with the second resonator, wherein no inductor is connected in parallel with the first resonator, at least one of the series resonators is the second resonator, and the other of the series resonators and the one or more parallel resonators are the first resonator; the second resonator and the inductor exhibit a resonance point, a first antiresonance point located at a frequency lower than the resonance point, and a second antiresonance point located at a frequency higher than the resonance point; and the first antiresonance point and the second antiresonance point are set between a third antiresonance point and a fourth antiresonance point, where the third and fourth antiresonance points are defined as a would-be first antiresonance point and a would-be second antiresonance point of the second resonator and the inductor if the excitation efficiency of the second resonator were the same as that of the first resonator.