1. Field of the Invention
The present invention generally relates to an antenna, an antenna device, and a wireless device such as a mobile phone.
2. Description of the Related Art
Techniques are known for controlling the directivity of an antenna by switching a connection destination of a feeding point. For example, Japanese Laid-Open Patent Publication No. 2012-186562 (Patent Document 1) discloses an antenna including a switch for switching the directivity of a radiating conductor by controlling a feeding point to come into contact with either one of two end points of the radiating conductor.
On the other hand, Japanese Patent No. 4422767 (Patent Document 2) discloses an antenna that is operable in multiple frequency bands by having a feeding element and a parasitic element that are coupled without being in contact.
However, it has been difficult to control the directivity of an antenna that has a contactless feeding system as disclosed in Patent Document 2 where a feeding element connected to a feeding point is coupled to a radiating element (parasitic element) without being in contact. For example, the switching technique disclosed in Patent Document 1 that involves controlling the directivity of an antenna by switching the connection point of a feeding element to a radiating element cannot be implemented in the antenna disclosed in Patent Document 2 because the feeding element and the radiating element have to be coupled without being in contact. Also, various constrains may be imposed on the arrangement and shape of the feeding element in order to prevent coupling at unintended locations when a connection point is switched, for example.
In view of the above, there is a demand for a technique for controlling the directivity of an antenna having a feeding element and a radiating element that are coupled without being in contact.