| 摘要 |
PROBLEM TO BE SOLVED: To provide a branching filter capable of improving mutual isolation characteristics of a transmission side and a reception side, and a communication device using the same. SOLUTION: A branching filter includes an antenna terminal 33, a transmission-side filter 25 and a reception-side filter 26 which are connected in parallel to the antenna terminal 33, and a matching circuit 22 positioned between the antenna terminal 33 and the reception-side filter 26. The reception-side filter 26 is a ladder-type filter in which the frequency of a series resonator 12 is higher than the antiresonance frequency of a parallel resonator 11. The transmission-side filter 25 is a ladder-type filter and has the capacitance in the pass band of the reception-side filter 26, and, because of the capacitance, the inductance of the impedance of the reception-side filter 26, when seen from the antenna terminal side, is reduced. COPYRIGHT: (C)2005,JPO&NCIPI
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