Antenna structure

1. An antenna structure, comprising:

a dipole antenna element; and

a floating metal element, disposed adjacent to the dipole antenna element, wherein a vertical projection of the dipole antenna element at least partially overlaps the floating metal element;

wherein the antenna structure at least covers an operation frequency band;

wherein the floating metal element comprises a main portion, a first coupling portion, and a second coupling portion, and wherein the main portion is coupled between the first coupling portion and the second coupling portion; and

wherein a distance between the main portion of the floating metal element and the vertical projection of the dipole antenna element is longer than or equal to 1/40 wavelength of the operation frequency band.

2. The antenna structure as claimed in claim 1 , wherein the operation frequency band is from 2400 MHz to 2500 MHz.

3. The antenna structure as claimed in claim 1 , wherein the dipole antenna element comprises a first radiation element coupled to a positive feeding point, and a second radiation element coupled to a negative feeding point.

4. The antenna structure as claimed in claim 3 , wherein the first radiation element and the second radiation element are disposed on the same plane.

5. The antenna structure as claimed in claim 3 , wherein the first radiation element and the second radiation element are respectively disposed on different planes.

6. The antenna structure as claimed in claim 3 , wherein the first radiation element further comprises a first terminal bending portion, and the second radiation element further comprises a second terminal bending portion.

7. The antenna structure as claimed in claim 3 , wherein each of the first radiation element and the second radiation element substantially has a straight-line shape or an L-shape.

8. The antenna structure as claimed in claim 1 , wherein the floating metal element substantially has a U-shape.

9. The antenna structure as claimed in claim 1 , wherein the floating metal element substantially has an arc-shape.

10. The antenna structure as claimed in claim 1 , wherein the floating metal element further comprises a first terminal widening portion coupled to the first coupling portion.

11. The antenna structure as claimed in claim 1 , wherein the floating metal element further comprises a second terminal widening portion coupled to the second coupling portion.

12. The antenna structure as claimed in claim 1 , wherein a distance between the main portion of the floating metal element and the vertical projection of the dipole antenna element is shorter than or equal to 1/24 wavelength of the operation frequency band.

13. The antenna structure as claimed in claim 1 , wherein a length of the main portion of the floating metal element is from 9/40 wavelength to 4/15 wavelength of the operation frequency band.

14. The antenna structure as claimed in claim 1 , wherein a length of each of the first coupling portion and the second coupling portion of the floating metal element is longer than 1/30 wavelength of the operation frequency band.

15. The antenna structure as claimed in claim 1 , wherein a distance between the dipole antenna element and the floating metal element is longer than or equal to 0.2 mm.

16. The antenna structure as claimed in claim 1 , further comprising:

a dielectric substrate, wherein the dipole antenna element and the floating metal element are respectively disposed on different planes of the dielectric substrate.

17. The antenna structure as claimed in claim 16 , wherein the dielectric substrate is a two-layer PCB (Printed Circuit Board) or a six-layer PCB.

18. The antenna structure as claimed in claim 16 , further comprising:

a ground plane, disposed on the dielectric substrate, and having a clearance region, wherein the vertical projection of the dipole antenna element and a vertical projection of the floating metal element are inside the clearance region.