Patent ID: 7057558

Claim:
An antenna device for high frequency comprising: a radiator made of a planar conductor having one of shapes of: (i) a substantial circle whose diameter is a substantially half wavelength; (ii) a substantially regular polygon where a length of a diagonal line passing through a center point of the regular polygon is a substantially half wavelength; and (iii) a substantial quadrangle whose edge length is a substantially half wavelength; a ground plate separated from the radiator by a predetermined distance and disposed in parallel with the radiator; a first feeding port coupled to a first feeding point on the radiator; and a second feeding port coupled to a second feeding point on the radiator, wherein the first feeding point is disposed in a region where high-frequency voltage generated by feeding from the second feeding port is zero, and the second feeding point is disposed in a region where high-frequency voltage generated by feeding from the first feeding port is zero, and wherein a line segment passing through a center point of the radiator and the first feeding point and a line segment passing through the center point of the radiator and the second feeding point intersect at substantially right angles, and wherein a third feeding port is coupled to a center point of the radiator to isolate the third feeding port from the first and second feeding ports.