Planar antenna with ring-shaped radiation element of high ring ratio

Claim 1

A planar antenna comprising: a ground conductor; a first dielectric layer laminated on one surface of said ground conductor; a second dielectric layer laminated on a second surface of said ground conductor opposite said first dielectric layer; a rectangular radiation element laminated on said first dielectric layer on a surface opposite said ground conductor, wherein a rectangular opening is formed through said radiation element at substantially a central area thereof so as to provide a ring-shaped radiation element and feed points are respectively disposed near center portions of two perpendicular sides of said opening, whereby the ratio of the length of one side of the rectangular opening divided by the length of one side of the rectangular radiation element is not greater than 0.6, and wherein said radiation element maintains a substantially isotropic property for generating two independent orthogonal propagation modes at substantially equal resonant frequencies and for producing a circularly polarized wave; a feed line provided on said second dielectric layer on a surface thereof opposite said ground conductor, wherein said feed line is coupled to said radiation element by way of two through-holes in said radiation element, said ground conductor, and said first and second dielectric layers; and a coaxial connector connected to said feed line, said coaxial connector mounted on the side of said second dielectric layer and aligned axially therewith.