To suppress a mode for propagation of an electromagnetic wave through a dielectric layer installed for matching purpose on a slot and to enable emission of a circularly polarized wave as the electromagnetic wave.

A spatial resonator is formed, which is surrounded with an upper main conductor layer 2 having a circular opening 5 of an upper face of a dielectric base 1, a lower main conductor layer 3, and an antenna conductor wall consisting of a plurality of through-conductors 6 electrically connecting the upper lower main conductor layers 2, 3 around the opening 5 and a sub- conductor layer 7 electrically connecting them, and a cross type slot 4 for feeding is formed to the lower main conductor layer 3. Then the thickness of the spatial resonator is selected to be λ0/8-λ0/2, the diameter of the opening 5 is selected to be λ0/2-3λ0/2, the length of the cross shaped slot 4 is selected to be λ0/4-3λ0/4 and the two slots are in crossing as a cross, where λ0 is the wavelength of a high frequency signal.