Patent ID: 8093961

Claim:
A duplexer formed on a piezoelectric substrate, the duplexer comprising: an antenna port formed on a center portion toward a rearward side of the piezoelectric substrate; a first signal port positioned more forward than the antenna port; a second signal port positioned more forward than the antenna port; a low band side filter provided at one side relative to a center of the antenna port between the first signal port and the antenna port and formed of a ladder-type filter including elastic wave resonators that form series arms and elastic wave resonators that form parallel arms, wherein a first parallel arm is formed at a stage closest to the first signal port and a second parallel arm is formed at a stage closer to the antenna port than the stage closest to the first signal port; and a high band side filter having a pass band higher than that of the low band side filter, provided at another side relative to the center of the antenna port opposite said one side between the second signal port and the antenna port, and formed of a ladder-type filter including elastic wave resonators that form series arms and elastic wave resonators that form parallel arms, wherein a third parallel arm is formed at a stage closest to the second signal port and a fourth parallel arm is formed at a stage closer to the antenna port than the stage closest to the second signal port; and wherein a ground side of the second parallel arm and a ground side of the fourth parallel arm are mutually connected via a conductive path that is formed toward the rearward side, rearward of the antenna port, away from a forward side of the first signal port and away from a forward side of the second signal port, the second parallel arm provided at a position rearward of the first parallel arm and the fourth parallel arm provided at a position rearward of the third parallel arm.