Antenna device having multiple resonant frequencies and radio apparatus

1. An antenna device included in a radio apparatus having a printed board, comprising:

a ground conductor provided in the printed board;

a first sub-element formed as an area having a first side and a second side crossing each other, the first side facing a side of the ground conductor, and the first sub-element having a feed portion at a crossing of the first side and the second side, wherein the first side, the second side, and the ground conductor extend along a same plane;

a second sub-element formed to branch off from the first sub-element around an end of the second side which is farther from the crossing, the second sub-element having an open end, and the second sub-element being directed at least partially in a direction opposite a direction from the crossing to an end of the first side opposite the crossing; and

a short circuit element short-circuiting the first sub-element with the ground conductor,

wherein the short circuit element branches off from the first sub-element at a point between the feed portion and the end of the second side which is farther from the crossing, and

wherein a width of the first sub-element is greater than widths of the second sub-element and the short circuit element, and wherein the area of the first sub-element is greater than areas of the second sub-element and the short circuit element.

2. The antenna device of claim 1 , wherein the antenna device has a resonant frequency determined by a path length from the feed portion to the open end of the second sub-element.

3. The antenna device of claim 1 , wherein the antenna device has a resonant frequency determined by a path length from the feed portion and along a fringe of the first sub-element, the fringe including the first side.

4. An antenna device included in a radio apparatus having a printed board, comprising: a ground conductor provided in the printed board;

a first sub-element formed as an area having a first side facing a side of the ground conductor and a second side being in a direction crossing the side of the ground conductor, the first side, the second side, and the ground conductor extending along a same plane, and the first sub-element having a feed portion at a first end of the first side which is closer to the second side; a second sub-element formed to branch off from the first sub-element around an end of the second side which is farther from the feed portion, the second sub-element being directed at least partially in a direction opposite a direction from the feed portion to a second end of the first side opposite the first end, and the second sub-element having an open end; and

a short circuit element short-circuiting the first sub-element with the ground conductor, wherein the short circuit element branches off from the first sub-element at a point between the feed portion and the end of the second side which is farther from the feed portion, and wherein a width of the first sub-element is greater than widths of the second sub-element and the short circuit element, and wherein the area of the first sub-element is greater than areas of the second sub-element and the short circuit element.

5. The antenna device of claim 4 , wherein the antenna device has a resonant frequency determined by a path length from the feed portion to the open end of the second sub-element.

6. The antenna device of claim 4 , wherein the antenna device has a resonant frequency determined by a path length from the feed portion and along a fringe of the first sub-element, the fringe including the first side.

7. A radio apparatus, comprising: a printed board having a ground conductor; and an antenna having a first sub-element, a second sub-element and a short-circuit element, wherein the first sub-element is formed as an area having a first side facing a side of the ground conductor and a second side being in a direction crossing the side of the ground conductor, the first side, the second side, and the ground conductor extending along a same plane, and the first sub-element having a feed portion at a first end of the first side which is closer to the second side, wherein the second sub-element is formed to branch off from the first sub-element around an end of the second side which is farther from the feed portion, the second sub-element being directed at least partially in a direction opposite a direction from the feed portion to a second end of the first side opposite the first end, and the second sub-element having an open end, wherein the short circuit element short-circuits the first sub-element with the ground conductor, and wherein the short circuit element branches off from the first sub-element at a point between the feed portion and the end of the second side which is farther from the feed portion, and wherein a width of the first sub-element is greater than widths of the second sub-element and the short circuit element, and wherein the area of the first sub-element is greater than areas of the second sub-element and the short circuit element.

8. The antenna device of claim 7 , wherein the antenna device has a resonant frequency determined by a path length from the feed portion to the open end of the second sub-element.

9. The antenna device of claim 7 , wherein the antenna device has a resonant frequency determined by a path length from the feed portion and along a fringe of the first sub-element, the fringe including the first side.