Antenna apparatus

An antenna apparatus, comprising:

• an antenna element;
• a feeder connected to the antenna element;
• a matching circuit connected to the feeder;
• a feeding point connected to the matching circuit;
• and
• a ground plate, on which the feeding point and the matching circuit are mounted,
• wherein the antenna element includes:
• a first plate section connected to the feeder, the first plate section extending into a direction of going away from the ground plate in parallel with an extending direction of the ground plate;
• a second plate section extending from an apical end of the first plate section almost perpendicularly;
• and
• a third plate section extending from an apical end of the second plate section into a direction of coming closer to the ground plate in parallel with the first plate section;
• wherein the ground plate can freely be folded up to the extending direction thereof;
• and
• wherein when an interval of a gap from the ground plate to the antenna element, the interval formed by the feeder, is denoted by G, a length from the ground plate to an outer end portion of the second plate section is denoted by L, and a ratio of the interval G to the length L is denoted by R, the interval G, the length L, and the ratio R satisfy formulae (1)-(3),
• G=R·L (1),
• 3.5 mm≦L≦11 mm (2), and
• 0.06≦R≦0.95 (3).