| 摘要 |
PROBLEM TO BE SOLVED: To provide a band pass filter, in which a configuration, miniaturization, reduction of weight and tuning are made simple, flexibility is improved while having variable characteristics and an application range is wide. SOLUTION: The logical configuration diagram of a serial multistage type band pass filter 30 configured by respectively adding amplifiers to two band pass filters 20 one by one and further serially connecting them is shown in figure 16. For example, by sequentially connecting filters and amplifiers like such a band pass filter 30, a circuit simultaneously fulfilling both desired filter characteristics and amplifier characteristics can be configured. As an amplifier to be used here, the amplifier of wide band such as a distributed amplifier, for example, is suitable. Further, it is preferable that a function as an isolator is presented. In such a configuration, for example, the band pass filter, in which the fluctuation of an amplification factor in respect to a frequency change is sharp, bandwidth is narrow and a central frequency is variable, can be formed or is easily formed compact and thin.
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