PURPOSE: To realize a very-wide-band, high-gain antenna by expanding self-complement principle to one element antenna in case of a stack antenna constituted by stacking numbers of elements longitudinally and laterally.

CONSTITUTION: A figure (a) is an explanatory drawing of the constitution principle of an element antenna. In the drawing, 1 is an infinite-width conductor plate where elements are arranged and 2 is a feeding point of the element antenna; and 3 is an edge of the conductor plate constituting a radiation element, and 4 is an edge of a slot while 3 and 4 are in shapes symmetrical with respect to a straight line 5. The antenna system constituted by arranging an infinite number of elements as shown in a figure (b) is a self-complementary antenna on the whole. Input impedance viewed from the feeding terminal of each element is invariably constant regardless of the shape of edges of conductors constituting the element antenna and a frequency. There is a monopole notch array antenna shown in a figure (c) as a high-gain element based upon said principle. In the figure, 1 is the feeding point. The input impedance at each feeding point when numbers of elements mentioned above are arranged as shown in a figure (b) is 188Ω regardless of the frequency.