| 摘要 |
PROBLEM TO BE SOLVED: To provide an inexpensive tunable filter which can regulate the central frequency electrically through a simple arrangement and can be mounted on an apparatus easily. SOLUTION: The tunable filter comprises rectangular waveguides 11 and 12 divided into two, a three layer substrate 13 held between the rectangular waveguides divided into two and provided with resonators 203-205, and active elements 304-306 mounted in the resonators wherein the central frequency and/or the bandwidth is regulated by applying a bias voltage to the active elements from the outside of the three layer substrate through the line pattern of the inner layer of the three layer substrate. The line pattern of the inner layer of the three layer substrate can be utilized as a line for applying a bias voltage and a varactor diode can be employed as the active element. A low-pass filter for attenuating a high frequency signal and preventing leak of a signal to the outside can be provided in the line for applying a bias voltage. COPYRIGHT: (C)2007,JPO&INPIT
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