A monoconical antenna (1) comprising: a cavity (11) with a substantially conical region or base region and a region vertex portion formed in the first end face of a dielectric (10); a radiation electrode (12) disposed on the surface of said concavity (11) or a radiation electrode (12) arranged so that said concavity (11) is filled with it; and a ground conductor (13) disposed in the vicinity of, and substantially parallel to, the other end face opposite to the first face of said dielectric (10), and is so constituted that electrical signals are fed between the region or vertex region of said radiation electrode (12) and said grounding conductor (13), wherein the cone angle of said region vertex portion, between a central axis and the surface of the concavity, is less than 90 degrees, wherein the cone angle of said concavity (11) decreases stepwise or continuously from the region or area based on the region vertex portion, and that the ratio of the height h of said concavity (11) the effective radius r of the region or zone base said concavity (11) is determined by the following expression which describes its relation with relative dielectric constant of said dielectric epsilonr (10): tan -1 (r / h) 0.8 or tang -1 (1.7 / epsilon r) + 13 (Unit angle: degree)
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