The size and thickness of wireless mobile communication apparatuses, such as mobile phones, have been rapidly reduced. Portable wireless communication apparatuses have been transformed from apparatuses to be used only as conventional telephones, to data terminals for transmitting and receiving electronic mails and for browsing web pages of WWW (World Wide Web), etc. Further, since the amount of information to be handled has increased from that of conventional audio and text information to that of pictures and videos, a further improvement in communication quality is required. In addition, portable wireless communication apparatuses are required to handle various applications, including telephone call for voices, data communication for browsing web pages, watching of television broadcasts, etc. In such circumstances, an antenna apparatus operable over a wide frequency range is required for wireless communications of the respective applications.
Conventionally, for example, antenna apparatuses described in Patent Literatures 1 and 2 have been known as antenna apparatuses covering multiple frequency bands.
Patent Literature 1 discloses a two-frequency antenna operable in two frequencies. The two-frequency antenna is characterized by having: elements printed on the front side of a dielectric substrate, including a feed line, an inner radiating element connected to the feed line, and an outer radiating element; an inductor connecting the inner and outer radiating elements printed on the front side of the dielectric substrate; elements printed on the back side of the dielectric substrate, including a feed line, an inner radiating element connected to the feed line, and an outer radiating element; and an inductor connecting the inner and outer radiating elements printed on the back side of the dielectric substrate. The two-frequency antenna of Patent Literature 1 has the inductors each inserted between the inner and outer radiating elements, thus forming a parallel resonant circuit of the inserted inductor and the parasitic capacitance between the elements. Since the parallel resonant circuit is open at a specific frequency when viewed from the antenna feed, only the inner radiating element (i.e., a portion from a feed line to the parallel resonant circuit) is excited at the specific frequency, and both the inner and outer radiating elements (i.e., portions on both sides of the parallel resonant circuit) are excited at the other frequencies. Accordingly, the two-frequency antenna of Patent Literature 1 can achieve multi-band characteristics.
A multi-band antenna of Patent Literature 2 has an antenna element including a first and a second radiating elements connected to both ends of an LC parallel resonant circuit, and is characterized in that the LC parallel resonant circuit is configured by the self-resonance of an inductor itself. The multi-band antenna of Patent Literature 2 can achieve multi-band characteristics by the LC parallel resonant circuit configured by the self-resonance of the radiating elements themselves.