WE CLAIM:
1. An antenna device comprising:
a metal housing having an aperture;
a first conductor disposed in a portion except for the aperture of the metal housing, the first conductor being capacitively coupled to the metal housing; and
a second conductor disposed in the aperture of the metal housing and in a same plane as that of the first conductor between which an alternating-current voltage is applied, the second conductor being transparent to visible light.
2. The antenna device according to claim 1,
wherein, of the first conductor and the second conductor, at least the second conductor is a transparent conductive film.
3. The antenna device according to claim 1, further comprising: a feed substrate including a first metal pattern connected to the first conductor; and a second metal pattern connected to the second conductor, the feed substrate for applying an alternating-current voltage to the first conductor and the second conductor via the first metal pattern and the second metal pattern.
4. The antenna device according to claim 3, wherein the feed substrate applies an alternating-current voltage to the second metal pattern via a matching circuit.
5. An antenna device comprising:
a metal housing having an aperture;
a third conductor disposed in a portion except for the aperture of the metal

housing, the third conductor being bent along a corner portion of the aperture, and the third conductor being capacitively coupled to the metal housing;
a fourth conductor disposed in the aperture of the metal housing and in a same plane as that of the third conductor, the fourth conductor being transparent to visible light; and
a fifth conductor disposed in the aperture of the metal housing and in a same plane as that of the third conductor between which an alternating-current voltage is applied, the fifth conductor being perpendicular to the fourth conductor and being transparent to visible light,
wherein the fourth conductor and the fifth conductor form an inverted-F antenna by being sequentially connected to the third conductor.
6. The antenna device according to claim 5,
wherein, in the inverted-F antenna, at least the fourth conductor and the fifth conductor are a transparent conductive film.
7. The antenna device according to claim 5, further comprising a feed substrate including a first metal pattern connected to the third conductor; and a second metal pattern connected to the fifth conductor, the feed substrate for applying an alternating-current voltage to the third conductor and the fifth conductor via the first metal pattern and the second metal pattern.
8. The antenna device according to claim 7,
wherein the feed substrate applies an alternating-current voltage to the second metal pattern via a matching circuit.