Multiplexer/branching filter

Abstract

The present invention relates to a multiplexer/demultiplexer for use in mobile communication devices and provides a small and low-loss multiplexer/demultiplexer. The present invention provides a multiplexer/demultiplexer including a first to a third ports each externally terminated with a pure resistance, in which the second port is made to be a common port by connecting between the first port and the ground a first resonant circuit which makes serial resonance at a frequency within a first frequency band or in its proximity, and further connecting an inductive element in series between the first port and the second port, and connecting between the third port and the ground a second resonant circuit which makes serial resonance at a frequency within a second frequency band which is different from the first frequency band or in its proximity, and further connecting a capacitive element in series between the third port and the second port.

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