Patent ID: 8249544

Claim:
A directional coupler comprising: a main-line; a sub-line configured to detect current flowing in the main-line; and a ground plane, wherein the sub-line includes a first line arranged to be nearer to the ground plane than is the main-line and arranged to be substantially parallel to the main-line and the ground plane; a second line running substantially parallel to the first line and provided on an opposite side of the main-line with respect to said first line in plan view from above the ground plane, and arranged to be substantially parallel to the main-line and the ground plane; a first vertical line having one end connected to an end portion of the first line and extending in a direction away from the ground plane so as to be substantially vertical with respect to the main-line; a third line having an end connected to another end of first vertical line and extending substantially parallel to the main-line and the ground plane, and overlapping with the first line when viewing the ground plane in plan view; a fourth line having one end connected to an end portion of the third line, extending to an opposite side of the main-line with respect to said third line in plan view from above the ground plane, and being substantially parallel to the ground plane; a fifth line having one end connected to another end of fourth line, extending substantially parallel to the main-line and the ground plane, and overlapping with the second line when viewing the ground plane in plan view; and a second vertical line having one end connected to an end portion of the fifth line, extending in a direction away from the ground plane so as to be substantially vertical with respect to the main-line, and being connected to an end portion of the second line, and wherein the directional coupler is constructed so that the first line to the fifth line and the first and second vertical lines of the sub-line form a loop, said loop being disposed to that a main component of a magnetic field vector vertically penetrating the loop is horizontal with respect to the ground plane.