| 摘要 |
PURPOSE: To provide a directional coupler, free in coupling mode, provided with the function of a low-pass filter as well. CONSTITUTION: The directional coupler in the figure is composed of a lumped parameter circuit. First of all, a low-pass filter 25a is arranged at a transmission line between terminals 21 and 22, and a low-pass filter 25b is arranged at a transmission line between terminals 23 and 24 as well. A 90 deg. phase shift circuit is constituted by suitably setting the values of two inductances and ground capacitances of the low-pass filter 25a (or 25b). The transmission line between the terminals 21 and 22 and the transmission line between the terminals 23 and 24 are respectively connected by capacitances 26a and 26b before and behind the low-pass filters 25a and 25b. The degree of coupling between both transmission lines is decided corresponding to the values of both capacitances 26a and 26b. The configuration of a phase shift line for the length ofλg/ 4 is eliminated and the physical position relation between both transmission lines to be paired is made comparatively free.
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