Tunable antenna device and radio apparatus

1. An antenna device configured to be fed at a feed portion included in a printed board of a radio apparatus, the antenna device comprising:

a feed element connected to the feed portion;

a first parasitic element having a first end portion and a second end portion, the first end portion being arranged closer to at least a portion of the feed element than the second end portion so as to be electrically coupled to the feed element, the first parasitic element being loaded with a first frequency shifter so that a resonant frequency of the first parasitic element is rendered variable; and

a second parasitic element having a third end portion and a fourth end portion, the third end portion being arranged closer to at least a portion of the feed element than the fourth end portion so as to be electrically coupled to the feed element, the second parasitic element being loaded with a second frequency shifter so that a resonant frequency of the second parasitic element is rendered variable.

2. The antenna device of claim 1 , wherein the first frequency shifter and the second frequency shifter each include one of a switch element and a reactance element of one of a variable value and a fixed value.

3. The antenna device of claim 1 , wherein the first frequency shifter and the second frequency shifter each include one of a switch element and a reactance element of one of a variable value and a fixed value, the reactance element being given a value in such a way that a range of a variable resonant frequency of the first parasitic element and a range of a variable resonant frequency of the second parasitic element may at least partially overlap.

4. The antenna device of claim 1 , wherein the first end portion is arranged close to a portion of the feed element at and around which a relatively high electric field is distributed upon being excited, and the second end portion is grounded.

5. The antenna device of claim 1 , wherein the first end portion is arranged close to a portion of the feed element at and around which a relatively high electric field is distributed upon being excited, and the second end portion is open-ended.

6. The antenna device of claim 1 , wherein the second end portion is grounded and arranged close to the feed portion.

7. The antenna device of claim 1 , wherein the first end portion is arranged close to a portion of the feed element at and around which a relatively high electric field is distributed upon being excited, and the first frequency shifter is arranged close to a ground portion of the printed board.

8. The antenna device of claim 1 , wherein the first end portion is arranged close and almost parallel to at least a portion of the feed element.

9. A radio apparatus, comprising:

a printed board including a feed portion and a ground portion; and

an antenna device configured to be fed at the feed portion, the antenna device comprising:

a feed element connected to the feed portion;

a first parasitic element having a first end portion and a second end portion, the first end portion being arranged closer to at least a portion of the feed element than the second end portion so as to be electrically coupled to the feed element, the first parasitic element being loaded with a first frequency shifter so that a resonant frequency of the first parasitic element is rendered variable; and

a second parasitic element having a third end portion and a fourth end portion, the third end portion being arranged closer to at least a portion of the feed element than the fourth end portion so as to be electrically coupled to the feed element, the second parasitic element being loaded with a second frequency shifter so that a resonant frequency of the second parasitic element is rendered variable.

10. The radio apparatus of claim 9 , wherein the first frequency shifter and the second frequency shifter each include one of a switch element and a reactance element of one of a variable value and a fixed value.

11. The radio apparatus of claim 9 , wherein the first frequency shifter and the second frequency shifter each include one of a switch element and a reactance element of one of a variable value and a fixed value, the reactance element being given a value in such a way that a range of a variable resonant frequency of the first parasitic element and a range of a variable resonant frequency of the second parasitic element may at least partially overlap.

12. The radio apparatus of claim 9 , wherein the first end portion is arranged close to a portion of the feed element at and around which a relatively high electric field is distributed upon being excited, and the second end portion is grounded.

13. The radio apparatus of claim 9 , wherein the first end portion is arranged close to a portion of the feed element at and around which a relatively high electric field is distributed upon being excited, and the second end portion is open-ended.

14. The radio apparatus of claim 9 , wherein the second end portion is grounded and arranged close to the feed portion.

15. The radio apparatus of claim 9 , wherein the first end portion is arranged close to a portion of the feed element at and around which a relatively high electric field is distributed upon being excited, and the first frequency shifter is arranged close to the ground portion of the printed board.

16. The radio apparatus of claim 9 , wherein the first end portion is arranged close and almost parallel to at least a portion of the feed element.