| 摘要 |
A directional coupler (500), which comprises a dielectric substrate (501) on top of a metal plate (510), is functioning as a ground plane. The transmission path is a suspended stripling so that there is a recess on the ground plane below the transmission conductor (520) being on the surface of the substrate. The sensing conductor (530) is a very small-sized conductive strip on the surface of the substrate. It has been connected from its head end to the measurement port (P3) and from its tail end via a termination resistor (550) to a small ground strip (515). The ground strip is next to the sensing conductor on the side of the output port (P2) of the directional coupler. With such an asymmetric structure, some directivity is obtained despite the small size of the sensing conductor. Also below the sensing conductor (530) there is a recess (506) on the ground plane, which joins the recess below the transmission conductor (520). By dimensioning the recess below the sensing conductor suitably, the velocities of the even and odd waveform occurring in the line constituted by it and the ground plane are obtained the same and thus directivity can be improved. The directional coupler is very space saving on the circuit board. As the substrate, an ordinary circuit board material can be used, whereby the board can have in addition to the directional coupler also other parts of radio-frequency circuits. The directional coupler does not require tuning in production. |
