Patent ID: 8773317

Claim:
An antenna apparatus comprising first and second feed ports respectively provided at positions on single planar antenna element, the single planar antenna element being simultaneously excited through the first and second feed ports so as to simultaneously operate as first and second portions respectively associated with the first and second feed ports, wherein the antenna apparatus further comprises: a slit provided on the single planar antenna element between the first and second feed ports; a resonant circuit, which is provided at a location along the slit, with a distance from an opening of the slit, and which is substantially short-circuited at a predetermined resonance frequency and is substantially open at frequencies away from the resonance frequency; and a controller for operating the antenna apparatus at a first isolation frequency identical to the resonance frequency of the resonant circuit, and at a second isolation frequency lower than the first isolation frequency, wherein when the antenna apparatus operates at the first isolation frequency, the resonant circuit is substantially short-circuited, and only a section of the slit from the opening to the resonant circuit resonates, thereby providing isolation between the first and second feed ports at the first isolation frequency, and when the antenna apparatus operates at the second isolation frequency, the resonant circuit is substantially open, and the entire slit resonates, thereby providing isolation between the first and second feed ports at the second isolation frequency.