| 摘要 |
First and second directional couplers each having a primary arm, a through arm and two secondary arms with a resonant circuit constructed to include the two secondary arms of each directional coupler. The directional filter forms a four port device with signals of a first frequency being applied to the first port and coupled to the fourth port by the resonant circuit, and signals applied to the third port being conveyed directly to the first port. Signals other than those at the first frequency are not coupled between the first and fourth ports.
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