PURPOSE: To miniaturize an antenna and to obtain satisfactory electric characteristics by giving the multistage constitution where the thickness of a dielectric substrate forming an annular patch of an annular antenna is approximately equal to that of a dielectric substrate where a micro strip line is formed.

CONSTITUTION: An annular antenna 2 having an outside radius a0 and an inside radius a1 is formed on a dielectric substrate 1 having thickness h1. A micro strip line 3 and a ground conductor 4 are formed on a dielectric substrate 6 having thickness h2, and dielectric substrates 1 and 6 are put one over the other. The multistage structure is given where the thickness of the dielectric substrate 1 in the part for formation of an annular patch having a radius a from the center of the annular antenna 2 is approximately equalized to that of the dielectric substrate 6 and the thickness of the dielectric substrate 1 is made larger than that of the dielectric substrate 6 in the other part. Thus, the antenna which is small-sized and has a wide band and has a good compatibility with a feed line is obtained.