Patent ID: 7012481

Claim:
A duplexer comprising a laminate in which dielectric layers and electrode layers are laminated alternately, the laminate comprising a first dielectric layer, a second dielectric layer, a third dielectric layer, and a fourth dielectric layer laminated successively, the duplexer comprising: a first filter for transmitting and a second filter for receiving, which are provided in the laminate and have different pass band frequencies; and a matching circuit comprising a coupling line formed in a planar shape on one plane of a laminated layer, having one end that is short-circuited and the other end that is connected to an external terminal, provided between the first filter and the second filter, a width of the coupling line being uniform from one end to the other end, wherein the electrode layers include: a first shield electrode placed on an upper surface of the first dielectric layer; an interstage coupling capacitive electrode comprising the first filter and an input/output coupling capacitive electrode comprising the second filter, placed between the first dielectric layer and the second dielectric layer; a first resonator electrode comprising the first filter, a second resonator electrode comprising the second filter, and a coupling line electrode comprising the matching circuit, placed between the second dielectric layer and the third dielectric layer; an input/output coupling capacitive electrode comprising the first filter and an interstage coupling capacitive electrode comprising the second filter, placed between the third dielectric layer and the fourth dielectric layer; a second shield electrode placed on a lower surface of the fourth dielectric layer; at least three terminal electrodes connected to the input/output coupling capacitive electrode comprising the first filter, the input/output coupling capacitive electrode comprising the second filter, and the coupling line electrode, respectively, provided on side surfaces of the first dielectric layer, the second dielectric layer, the third dielectric layer, and the fourth dielectric layer; and an end face electrode connecting the first shield electrode and the second shield electrode to each other, wherein the first filter comprises at least one first stripline resonator formed in a planar shape on the one plane, having one end that is short-circuited, the second filter comprises at least one second stripline resonator formed in a planar shape on the one plane, having one end that is short-circuited, the external terminal connected to the coupling line is on a short-circuited side of the first filter and the second filter, and the first stripline resonator and the second stripline resonator are coupled to the coupling line by electromagnetic field coupling.