Patent ID: 7821354

Claim:
A directional coupler which comprises a dielectric substrate on top of a metal plate functioning as a ground plane, an input port, an output port and a transmission path between them, which path is a suspended stripline so that there is a recess on the ground plane below a transmission conductor on a surface of the substrate, a sensing conductor, which is a conductive strip on the surface of the substrate, a head end of the sensing conductor being connected to a measurement port of the directional coupler and a tail end being connected to a termination resistor, wherein the sensing conductor is substantially smaller than an eighth of a wavelength, the directional coupler further comprises a ground strip connected to the ground plane to obtain directivity, which ground strip is located next to the sensing conductor on the side of the output port, and to which ground strip one end of said termination resistor has been connected, and there is a recess on the ground plane also below the sensing conductor to improve directivity.