Patent ID: 7808435
Filing Date: 2010-10-05
Classification: H01Q

Abstract:
1. An antenna structure comprising: a circuit board, a base mounted in a ground region of said circuit board, the base having provided thereon a driven radiating electrode that is electrically connected to a wireless communication circuit and that performs antenna operations in a plurality of resonant frequency bands different from each other, and a parasitic radiating electrode electromagnetically coupled to the driven radiating electrode with a space between the parasitic radiating electrode and the driven radiating electrode; the driven radiating electrode being a radiating electrode having one end that serves as a feeding end electrically connected to the wireless communication circuit and the other end that serves as an open end, the driven radiating electrode having such a form that the feeding end and the open end thereof are provided adjacent to each other with a space therebetween so that a loop-shaped current path is formed between the feeding end and the open end; the parasitic radiating electrode performing an antenna operation with the driven radiating electrode through electromagnetic coupling with the driven radiating electrode so as to cause multiple resonance at least in a harmonic resonant frequency band, the harmonic resonant frequency band being higher than a base resonant frequency band, the base resonant frequency band being lowest among the plurality of resonant frequency bands of the driven radiating electrode, the antenna structure further comprising: capacitance loading means for loading a capacitance to a harmonic-mode zero-voltage region of the driven radiating electrode, the harmonic-mode zero-voltage region being a region where a voltage becomes zero or nearly zero in a harmonic mode, the harmonic mode being an antenna operation mode in the harmonic resonant frequency band; a grounding conduction path that electrically connects a ground electrode with the capacitance loading means, the ground electrode being formed in the ground region on the circuit board; and switching means, provided in the grounding conduction path, for switching conduction ON/OFF between the capacitance loading means and the ground electrode on the circuit board to control switching between ON and OFF of capacitance loading by the capacitance loading means to the harmonic-mode zero-voltage region of the driven radiating electrode, thereby switching a base resonant frequency in the base resonant frequency band of the driven radiating electrode.