| 摘要 |
In a directional coupler having four input/output terminals in a planar circuit using strip lines or microstrip lines, a quarter-wavelength line is connected between first and third terminals, and between second and fourth terminals, respectively, and furthermore between first and second terminals, and between third and fourth terminals, individually, a branch line is connected, having a length which is (2N+1)/4 wavelength, cascading (2N+1) pieces of quarter-wavelength lines (where N is a positive integer). These (2N+1) quarter-wavelength lines composing the branch lines are set so that lines of high characteristic impedance and lines of low characteristic impedance appear alternately. The (2N+1) quarter-wavelength lines in which the lines of high characteristic impedance and low characteristic impedance appear alternately function equivalently to (2N+1)/4 wavelength lines of a higher characteristic impedance, or equivalently to (2N+1)/4 wavelength lines of a lower characteristic impedance, thereby operating as a directional coupler having a small coupling coefficient or as a directional coupler of having a large coupling coefficient.
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