To provide a planar antenna having orthotropic, anisotropic radiation characteristics.

A dielectric substrate 11 is cut away at a position corresponding to a slot line 12 that is an electromagnetic wave propagation path, and a slit 14 that changes a relative dielectric constant is provided. Thus, a planar antenna 10 with an orthotropic, anisotropic radiation characteristics can be obtained. Furthermore, without having to cut a part of a dielectric substrate 71 corresponding to a slot line 72, a projecting part 75 is formed such that the dielectric substrate 71 is reduced gradually, with respect to an electromagnetic wave propagation direction. Thus, H-plane directivity obtains wide-angle characteristics, in comparison with conventional planar antennas, the orthotropic, anisotropic radiation characteristics can be obtained, and deterioration of the antenna radiation efficiency caused by surge impedance non-matching on the slot line 72 can be reduced.