| 摘要 |
<P>PROBLEM TO BE SOLVED: To obtain a coupler with a flat coupling degree over a wide band. <P>SOLUTION: A directional coupler comprises: a main line; an input port for inputting a transmission signal to the main line; an output port for outputting the transmission signal from the main line; a sub line for extracting a part of the transmission signal by electromagnetic field coupling with the main line; a coupling port provided on one end part of the sub line; and an isolation port provided on the other end part. A low-pass filter part having a function as a low-pass filter is provided between the sub line and the coupling port. By means of this low-pass filter part, a resonance point is formed at a higher region side than a used frequency band to flatten a coupling degree in the used frequency band. When a lower end frequency of the used frequency band is defined as F1, an upper end frequency is defined as F2, the center frequency is defined as Fc, band width is defined as BW, and a frequency of the resonance point is defined as Fr, (Fr-Fc)/Fc/BW is 0.6 to 1.2, more preferably, 0.65 to 0.9. <P>COPYRIGHT: (C)2013,JPO&INPIT |
