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 in a wide frequency range is required for wireless communications of the respective applications.
Conventional antenna apparatuses operable in a wide frequency band and capable of adjusting the resonance frequency include, for example, an antenna apparatus in which an antenna element is provided with a slit to adjust the resonance frequency, as disclosed in Patent Literature 1, and a notch antenna having a slit provided with a trap circuit, as disclosed in Patent Literature 2.
The antenna apparatus of Patent Literature 1 is configured to include a planar radiating element (radiating plate), a ground plate opposed thereto in parallel, a feed portion located at the middle of an edge of the radiating plate for supplying a radio frequency signal, a short-circuit portion for short-circuiting the radiating plate to the ground plate near the feed portion, and two resonators formed by providing a slit on the radiating plate at an edge opposed to the feed portion. The degree of coupling of the two resonators is optimized by adjusting the shape or dimensions of this slit or by loading a reactance element or a conductor plate across the slit. Thus, a small and low-profile antenna is obtained with suitable characteristics.
In the notch antenna of Patent Literature 2, when the notch antenna should resonate in a low communication frequency band, the slit can be open at the location of the trap circuit at a radio frequency, and when the notch antenna should resonate in a high communication frequency band, the slit can be closed at the location of the trap circuit at a radio frequency. In this manner, it is possible to appropriately change the resonant length of the notch antenna according to a communication frequency band in which the notch antenna should resonate.
In addition, an antenna apparatus of Patent Literature 3 is configured to include a substrate, a plurality of planar antenna elements on the substrate, and at least one isolation element located on the substrate between the antenna elements and grounded to a ground portion. The isolation element between the antenna elements can be used to prevent mutual interference between the antenna elements, thus preventing distortion in the radiation pattern. In addition, The isolation element can operate as a parasitic antenna by grounding the isolation element to a ground plane, thus increasing output gain. In addition, the isolation element and the antenna elements can be fabricated only by etching metal films stacked on the substrate into predetermined patterns, and thus, the fabrication method can be simplified, the isolation element can be made of the metal films on the substrate, the elements can be made in a nearly two-dimensional planar structure.