| 摘要 |
PROBLEM TO BE SOLVED: To make steep the attenuation characteristics of a filter device and a communication device which attenuate unwanted frequency components of a signal. SOLUTION: For example, a distributing means 1 distributes an object signal to be attenuated, a filter (BPF) 2 attenuates unwanted frequency components of one distributed signal, and an attenuating means 3 attenuates the other distributed signal, and a phase unit 4 and a delay circuit 5 put the signal attenuated by the filter 2 and the signal attenuated by the attenuating means 3 in phase relation, so that frequency components having the same amplitude cancel each other and a composing means 6 puts them together. Furthermore, a filter (BPF) 7 attenuates unwanted frequency components of the signal, after having been composed by the composing means 6 (or before being distributed by the distributing means 1).
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