| 摘要 |
A band-pass filter is provided to have a little phase change in a pass band and a steep frequency characteristic. The band-pass filter comprises a four-terminal pair and 90-degree hybrid circuit (10) and a band-elimination filter circuit. The hybrid circuit (10) distributes power to two portions, which have 90-degree phase differences with each other. The band-elimination filter has a plurality of connected unit circuits (15, 16) and resistances. Each of unit circuits (15, 16) is composed of a series circuit of an inductance coil and a capacitance and a parallel circuit of an inductance coil and a capacitance, wherein the series circuit is connected to the parallel circuit. Input terminals of the unit circuits (15, 16) are connected to coupling terminals (13, 14) of the hybrid circuit (10), respectively, while output terminals of the unit circuits (15, 16) are terminated by the resistances that have the same impedance values as output impedances of the unit circuits (15, 16), respectively.
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