| 摘要 |
PURPOSE:To improve the isolation characteristic of a three-branch line 3dB hybrid circuit, by partially cutting off the branched section of the central one among the lines which are connected in parallel with input-output lines and making the band for degree of coupling and band for isolation characteristic coincident with each other. CONSTITUTION:This three-branch line 3dB hybrid circuit is composed of 1st lines 5 and 8 and 2nd lines 6 and 7 which are connected in series with input-and output-side lines 1-4 and lines 9-11 which are connected with the lines 5-8 in parallel. By making the impedance of the 1st and 2nd lines 5 and 8, and 6 and 7, equal to the impedance of the input-and output-side lines 1-4 and providing notched sections 12 and 13 in the 1st and 2nd lines 5 and 8, and 6 and 7, in the vicinity of the branched sections of the central line 10 of the parallel lines 9-11, the center frequency for degree of coupling is made coincident with the center frequency for isolation. Therefore, the isolation characteristic of this hybrid circuit can be improved.
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