Patent ID: 7369088

Claim:
A circularly polarized microstrip antenna comprising: a dielectric substrate; a λ/2-type emitting electrode that generates circularly polarized waves on a front surface of the dielectric substrate; a coplanar signal line that feeds the emitting electrode on a back surface of the dielectric substrate; and a ground electrode on the back surface of the dielectric substrate, wherein the signal line is electromagnetically coupled to the emitting electrode and the ground electrode covers the entire area of the back surface of the dielectric substrate excluding a region in which the signal line is provided, wherein the signal line extends from an edge of the back surface of the dielectric substrate to a position between the edge of the back surface of the dielectric substrate and a center position of the emitting electrode on the back surface of the dielectric substrate, and wherein the signal line has a length that allows an image current in the around electrode to travel along paths that pass through the center position of the emitting electrode without being obstructed by the signal line for feeding the emitting electrode.