Duplexer including first and second additional grating reflectors
Disclosed is a miniaturized duplexer having a good isolation characteristic. A duplexer having a high band side filter and a low band side filter that are each formed in a ladder-type filter provided on a common piezoelectric substrate is provided with a first elastic wave resonator to be included in one of these filters, a second elastic wave resonator to be included in the other of the filters, and a first additional grating reflector provided between these resonators to reflect an elastic wave leaked from a grating reflector of the first elastic wave resonator, and in which an additional grating reflector is not provided on a side opposite to the second elastic wave resonator in the first elastic wave resonator.
1. 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.
2. The duplexer according to claim 1 , wherein the respective parallel arms in the high band side filter and the low band side filter are disposed in peripheral edge regions on the piezoelectric substrate, and ground ports are disposed around the periphery of the piezoelectric substrate, and the ground ports and the respective parallel arms are connected.
3. The duplexer according to claim 1 , wherein a pitch between electrode fingers provided in said additional grating reflectors is not less than 0.97 times nor more than 1.03 times a pitch between electrode fingers in the grating reflectors from which elastic waves to be reflected in said additional grating reflectors leak.
4. The duplexer according to claim 1 , wherein the electrode fingers provided in said additional grating reflectors are disposed to be each inclined with a narrow angle larger than 0° and smaller than 90° with respect to a direction in which elastic waves that leak from the grating reflectors and are reflected in said additional grating reflectors propagate.