A filter includes series units and shunt units. Each series unit includes at least one bulk acoustic wave resonator. Each shunt unit includes at least one bulk acoustic wave resonator and is disposed between one of the series units and a ground. One of the series units or one of the shunt units includes a first bulk acoustic wave resonator, a second bulk acoustic wave resonator, and a third bulk acoustic wave resonator connected in series. The second bulk acoustic wave resonator has a polarity different from a polarity of the first bulk acoustic wave resonator and a polarity of the third bulk acoustic wave resonator.