Patent ID: 8354895

Claim:
A duplexer provided with a high band side filter and a low band side filter provided on a common piezoelectric substrate, in which these filters are ladder-type filters including elastic wave resonators to be series arms each provided with grating reflectors at both ends of an IDT electrode and elastic wave resonators to be parallel arms each provided with grating reflectors at both ends of an IDT electrode, the duplexer comprising: a first elastic wave resonator included in one of the high band side filter and the low band side filter; a second elastic wave resonator included in the other of the high band side filter and the low band side filter and being adjacent to said first elastic wave resonator in a main propagation direction of elastic waves; a first additional grating reflector provided between said first elastic wave resonator and said second elastic wave resonator and for reflecting an elastic wave leaked from a grating reflector of said first elastic wave resonator; and a second additional grating reflector, provided between said first elastic wave resonator and said second elastic wave resonator, for reflecting an elastic wave leaked from a grating reflector of said second elastic wave resonator; wherein an additional grating reflector is not provided on a side opposite to said second elastic wave resonator in said first elastic wave resonator, nor on a side opposite to said first elastic wave resonator in said second elastic wave resonator, and wherein said second additional grating reflector is provided between the grating reflector of said first elastic wave resonator and said first additional grating reflector.